<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2023 Workiva-->
<!--r:533a9540-a072-4938-9946-d06b40d0a434,g:6f1bbe8c-8860-4a36-b7e7-40c71218c5ff-->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:mg="http://www.mistrasgroup.com/20221231" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:dtr-types="http://www.xbrl.org/dtr/type/2020-01-21" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="http://www.mistrasgroup.com/20221231">
  <xs:import namespace="http://fasb.org/srt/2022" schemaLocation="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd"/>
  <xs:import namespace="http://fasb.org/us-gaap/2022" schemaLocation="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd"/>
  <xs:import namespace="http://www.w3.org/1999/xlink" schemaLocation="http://www.xbrl.org/2003/xlink-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/2003/linkbase" schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/dtr/type/2020-01-21" schemaLocation="https://www.xbrl.org/dtr/type/2020-01-21/types.xsd"/>
  <xs:import namespace="http://xbrl.org/2005/xbrldt" schemaLocation="http://www.xbrl.org/2005/xbrldt-2005.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/country/2022" schemaLocation="https://xbrl.sec.gov/country/2022/country-2022.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/dei/2022" schemaLocation="https://xbrl.sec.gov/dei/2022/dei-2022.xsd"/>
  <xs:annotation>
    <xs:appinfo>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="mg-20221231_lab.xml" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="mg-20221231_pre.xml" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="mg-20221231_cal.xml" xlink:role="http://www.xbrl.org/2003/role/calculationLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="mg-20221231_def.xml" xlink:role="http://www.xbrl.org/2003/role/definitionLinkbaseRef" xlink:type="simple"/>
      <link:roleType id="Cover" roleURI="http://www.mistrasgroup.com/role/Cover">
        <link:definition>0000001 - Document - Cover</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AuditInformation" roleURI="http://www.mistrasgroup.com/role/AuditInformation">
        <link:definition>0000002 - Document - Audit Information</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConsolidatedBalanceSheets" roleURI="http://www.mistrasgroup.com/role/ConsolidatedBalanceSheets">
        <link:definition>0000003 - Statement - Consolidated Balance Sheets</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConsolidatedBalanceSheetsParenthetical" roleURI="http://www.mistrasgroup.com/role/ConsolidatedBalanceSheetsParenthetical">
        <link:definition>0000004 - Statement - Consolidated Balance Sheets (Parenthetical)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConsolidatedStatementsofIncomeLoss" roleURI="http://www.mistrasgroup.com/role/ConsolidatedStatementsofIncomeLoss">
        <link:definition>0000005 - Statement - Consolidated Statements of Income (Loss)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConsolidatedStatementsofComprehensiveIncomeLoss" roleURI="http://www.mistrasgroup.com/role/ConsolidatedStatementsofComprehensiveIncomeLoss">
        <link:definition>0000006 - Statement - Consolidated Statements of Comprehensive Income (Loss)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConsolidatedStatementsofEquity" roleURI="http://www.mistrasgroup.com/role/ConsolidatedStatementsofEquity">
        <link:definition>0000007 - Statement - Consolidated Statements of Equity</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConsolidatedStatementsofCashFlows" roleURI="http://www.mistrasgroup.com/role/ConsolidatedStatementsofCashFlows">
        <link:definition>0000008 - Statement - Consolidated Statements of Cash Flows</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryofSignificantAccountingPoliciesandPractices" roleURI="http://www.mistrasgroup.com/role/SummaryofSignificantAccountingPoliciesandPractices">
        <link:definition>0000009 - Disclosure - Summary of Significant Accounting Policies and Practices</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="Revenue" roleURI="http://www.mistrasgroup.com/role/Revenue">
        <link:definition>0000010 - Disclosure - Revenue</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EarningsperShare" roleURI="http://www.mistrasgroup.com/role/EarningsperShare">
        <link:definition>0000011 - Disclosure - Earnings per Share</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AccountsReceivable" roleURI="http://www.mistrasgroup.com/role/AccountsReceivable">
        <link:definition>0000012 - Disclosure - Accounts Receivable</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="Inventories" roleURI="http://www.mistrasgroup.com/role/Inventories">
        <link:definition>0000013 - Disclosure - Inventories</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="PropertyPlantandEquipment" roleURI="http://www.mistrasgroup.com/role/PropertyPlantandEquipment">
        <link:definition>0000014 - Disclosure - Property, Plant and Equipment</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="Acquisitions" roleURI="http://www.mistrasgroup.com/role/Acquisitions">
        <link:definition>0000015 - Disclosure - Acquisitions</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="Goodwill" roleURI="http://www.mistrasgroup.com/role/Goodwill">
        <link:definition>0000016 - Disclosure - Goodwill</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IntangibleAssets" roleURI="http://www.mistrasgroup.com/role/IntangibleAssets">
        <link:definition>0000017 - Disclosure - Intangible Assets</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AccruedExpensesandOtherCurrentLiabilities" roleURI="http://www.mistrasgroup.com/role/AccruedExpensesandOtherCurrentLiabilities">
        <link:definition>0000018 - Disclosure - Accrued Expenses and Other Current Liabilities</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LongTermDebt" roleURI="http://www.mistrasgroup.com/role/LongTermDebt">
        <link:definition>0000019 - Disclosure - Long-Term Debt</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueMeasurements" roleURI="http://www.mistrasgroup.com/role/FairValueMeasurements">
        <link:definition>0000020 - Disclosure - Fair Value Measurements</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareBasedCompensation" roleURI="http://www.mistrasgroup.com/role/ShareBasedCompensation">
        <link:definition>0000021 - Disclosure - Share-Based Compensation</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxes" roleURI="http://www.mistrasgroup.com/role/IncomeTaxes">
        <link:definition>0000022 - Disclosure - Income Taxes</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitPlans" roleURI="http://www.mistrasgroup.com/role/EmployeeBenefitPlans">
        <link:definition>0000023 - Disclosure - Employee Benefit Plans</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RelatedPartyTransactions" roleURI="http://www.mistrasgroup.com/role/RelatedPartyTransactions">
        <link:definition>0000024 - Disclosure - Related Party Transactions</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="Leases" roleURI="http://www.mistrasgroup.com/role/Leases">
        <link:definition>0000025 - Disclosure - Leases</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CommitmentsandContingencies" roleURI="http://www.mistrasgroup.com/role/CommitmentsandContingencies">
        <link:definition>0000026 - Disclosure - Commitments and Contingencies</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SegmentDisclosure" roleURI="http://www.mistrasgroup.com/role/SegmentDisclosure">
        <link:definition>0000027 - Disclosure - Segment Disclosure</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SelectedQuarterlyFinancialInformationunaudited" roleURI="http://www.mistrasgroup.com/role/SelectedQuarterlyFinancialInformationunaudited">
        <link:definition>0000028 - Disclosure - Selected Quarterly Financial Information (unaudited)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryofSignificantAccountingPoliciesandPracticesPolicies" roleURI="http://www.mistrasgroup.com/role/SummaryofSignificantAccountingPoliciesandPracticesPolicies">
        <link:definition>0000029 - Disclosure - Summary of Significant Accounting Policies and Practices (Policies)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenueTables" roleURI="http://www.mistrasgroup.com/role/RevenueTables">
        <link:definition>0000030 - Disclosure - Revenue (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EarningsperShareTables" roleURI="http://www.mistrasgroup.com/role/EarningsperShareTables">
        <link:definition>0000031 - Disclosure - Earnings per Share (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AccountsReceivableTables" roleURI="http://www.mistrasgroup.com/role/AccountsReceivableTables">
        <link:definition>0000032 - Disclosure - Accounts Receivable (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="InventoriesTables" roleURI="http://www.mistrasgroup.com/role/InventoriesTables">
        <link:definition>0000033 - Disclosure - Inventories (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="PropertyPlantandEquipmentTables" roleURI="http://www.mistrasgroup.com/role/PropertyPlantandEquipmentTables">
        <link:definition>0000034 - Disclosure - Property, Plant and Equipment (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AcquisitionsTables" roleURI="http://www.mistrasgroup.com/role/AcquisitionsTables">
        <link:definition>0000035 - Disclosure - Acquisitions (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GoodwillTables" roleURI="http://www.mistrasgroup.com/role/GoodwillTables">
        <link:definition>0000036 - Disclosure - Goodwill (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IntangibleAssetsTables" roleURI="http://www.mistrasgroup.com/role/IntangibleAssetsTables">
        <link:definition>0000037 - Disclosure - Intangible Assets (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AccruedExpensesandOtherCurrentLiabilitiesTables" roleURI="http://www.mistrasgroup.com/role/AccruedExpensesandOtherCurrentLiabilitiesTables">
        <link:definition>0000038 - Disclosure - Accrued Expenses and Other Current Liabilities (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LongTermDebtTables" roleURI="http://www.mistrasgroup.com/role/LongTermDebtTables">
        <link:definition>0000039 - Disclosure - Long-Term Debt (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueMeasurementsTables" roleURI="http://www.mistrasgroup.com/role/FairValueMeasurementsTables">
        <link:definition>0000040 - Disclosure - Fair Value Measurements (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareBasedCompensationTables" roleURI="http://www.mistrasgroup.com/role/ShareBasedCompensationTables">
        <link:definition>0000041 - Disclosure - Share-Based Compensation (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesTables" roleURI="http://www.mistrasgroup.com/role/IncomeTaxesTables">
        <link:definition>0000042 - Disclosure - Income Taxes (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeasesTables" roleURI="http://www.mistrasgroup.com/role/LeasesTables">
        <link:definition>0000043 - Disclosure - Leases (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SegmentDisclosureTables" roleURI="http://www.mistrasgroup.com/role/SegmentDisclosureTables">
        <link:definition>0000044 - Disclosure - Segment Disclosure (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SelectedQuarterlyFinancialInformationunauditedTables" roleURI="http://www.mistrasgroup.com/role/SelectedQuarterlyFinancialInformationunauditedTables">
        <link:definition>0000045 - Disclosure - Selected Quarterly Financial Information (unaudited) (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryofSignificantAccountingPoliciesandPracticesDetails" roleURI="http://www.mistrasgroup.com/role/SummaryofSignificantAccountingPoliciesandPracticesDetails">
        <link:definition>0000046 - Disclosure - Summary of Significant Accounting Policies and Practices (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenueNarrativeDetails" roleURI="http://www.mistrasgroup.com/role/RevenueNarrativeDetails">
        <link:definition>0000047 - Disclosure - Revenue - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenueNarrativeDetails_1" roleURI="http://www.mistrasgroup.com/role/RevenueNarrativeDetails_1">
        <link:definition>0000047 - Disclosure - Revenue - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenueDisaggregatedRevenuesbySegmentDetails" roleURI="http://www.mistrasgroup.com/role/RevenueDisaggregatedRevenuesbySegmentDetails">
        <link:definition>0000048 - Disclosure - Revenue - Disaggregated Revenues by Segment (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EarningsperShareComputationsofBasicandDilutedEarningsPerShareDetails" roleURI="http://www.mistrasgroup.com/role/EarningsperShareComputationsofBasicandDilutedEarningsPerShareDetails">
        <link:definition>0000049 - Disclosure - Earnings per Share - Computations of Basic and Diluted Earnings Per Share (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EarningsperSharePotentialCommonSharesExcludedFromComputationofDilutedEarningsDetails" roleURI="http://www.mistrasgroup.com/role/EarningsperSharePotentialCommonSharesExcludedFromComputationofDilutedEarningsDetails">
        <link:definition>0000050 - Disclosure - Earnings per Share - Potential Common Shares Excluded From Computation of Diluted Earnings (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AccountsReceivableSummaryDetails" roleURI="http://www.mistrasgroup.com/role/AccountsReceivableSummaryDetails">
        <link:definition>0000051 - Disclosure - Accounts Receivable - Summary (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AccountsReceivableNarrativeDetails" roleURI="http://www.mistrasgroup.com/role/AccountsReceivableNarrativeDetails">
        <link:definition>0000052 - Disclosure - Accounts Receivable - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="InventoriesDetails" roleURI="http://www.mistrasgroup.com/role/InventoriesDetails">
        <link:definition>0000053 - Disclosure - Inventories (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="PropertyPlantandEquipmentDetails" roleURI="http://www.mistrasgroup.com/role/PropertyPlantandEquipmentDetails">
        <link:definition>0000054 - Disclosure - Property, Plant and Equipment (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AcquisitionsNarrativeDetails" roleURI="http://www.mistrasgroup.com/role/AcquisitionsNarrativeDetails">
        <link:definition>0000055 - Disclosure - Acquisitions - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AcquisitionsAcquisitionRelatedExpenseDetails" roleURI="http://www.mistrasgroup.com/role/AcquisitionsAcquisitionRelatedExpenseDetails">
        <link:definition>0000056 - Disclosure - Acquisitions - Acquisition-Related Expense (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GoodwillChangesinCarryingAmountofGoodwillDetails" roleURI="http://www.mistrasgroup.com/role/GoodwillChangesinCarryingAmountofGoodwillDetails">
        <link:definition>0000057 - Disclosure - Goodwill - Changes in Carrying Amount of Goodwill (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GoodwillNarrativeDetails" roleURI="http://www.mistrasgroup.com/role/GoodwillNarrativeDetails">
        <link:definition>0000058 - Disclosure - Goodwill - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IntangibleAssetsGrossCarryingAmountandAccumulatedAmortizationDetails" roleURI="http://www.mistrasgroup.com/role/IntangibleAssetsGrossCarryingAmountandAccumulatedAmortizationDetails">
        <link:definition>0000059 - Disclosure - Intangible Assets - Gross Carrying Amount and Accumulated Amortization (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IntangibleAssetsNarrativeDetails" roleURI="http://www.mistrasgroup.com/role/IntangibleAssetsNarrativeDetails">
        <link:definition>0000060 - Disclosure - Intangible Assets - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IntangibleAssetsExpectedAmortizationExpenseDetails" roleURI="http://www.mistrasgroup.com/role/IntangibleAssetsExpectedAmortizationExpenseDetails">
        <link:definition>0000061 - Disclosure - Intangible Assets - Expected Amortization Expense (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AccruedExpensesandOtherCurrentLiabilitiesDetails" roleURI="http://www.mistrasgroup.com/role/AccruedExpensesandOtherCurrentLiabilitiesDetails">
        <link:definition>0000062 - Disclosure - Accrued Expenses and Other Current Liabilities (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LongTermDebtScheduleofLongTermDebtDetails" roleURI="http://www.mistrasgroup.com/role/LongTermDebtScheduleofLongTermDebtDetails">
        <link:definition>0000063 - Disclosure - Long-Term Debt - Schedule of Long-Term Debt (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LongTermDebtNarrativeDetails" roleURI="http://www.mistrasgroup.com/role/LongTermDebtNarrativeDetails">
        <link:definition>0000064 - Disclosure - Long-Term Debt - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LongTermDebtScheduledPrincipalPaymentsDetails" roleURI="http://www.mistrasgroup.com/role/LongTermDebtScheduledPrincipalPaymentsDetails">
        <link:definition>0000065 - Disclosure - Long-Term Debt - Scheduled Principal Payments (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueMeasurementsDetails" roleURI="http://www.mistrasgroup.com/role/FairValueMeasurementsDetails">
        <link:definition>0000066 - Disclosure - Fair Value Measurements (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareBasedCompensationLongtermIncentivePlansDetails" roleURI="http://www.mistrasgroup.com/role/ShareBasedCompensationLongtermIncentivePlansDetails">
        <link:definition>0000067 - Disclosure - Share-Based Compensation - Long-term Incentive Plans (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareBasedCompensationStockOptionsNarrativeDetails" roleURI="http://www.mistrasgroup.com/role/ShareBasedCompensationStockOptionsNarrativeDetails">
        <link:definition>0000068 - Disclosure - Share-Based Compensation - Stock Options Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareBasedCompensationStockOptionActivityDetails" roleURI="http://www.mistrasgroup.com/role/ShareBasedCompensationStockOptionActivityDetails">
        <link:definition>0000069 - Disclosure - Share-Based Compensation - Stock Option Activity (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareBasedCompensationRestrictedStockUnitsAwardsNarrativeDetails" roleURI="http://www.mistrasgroup.com/role/ShareBasedCompensationRestrictedStockUnitsAwardsNarrativeDetails">
        <link:definition>0000070 - Disclosure - Share-Based Compensation - Restricted Stock Units Awards Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareBasedCompensationVestingActivityofRestrictedStockUnitAwardsDetails" roleURI="http://www.mistrasgroup.com/role/ShareBasedCompensationVestingActivityofRestrictedStockUnitAwardsDetails">
        <link:definition>0000071 - Disclosure - Share-Based Compensation - Vesting Activity of Restricted Stock Unit Awards (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareBasedCompensationCommonStockIssuedtoNonemployeeDirectorsDetails" roleURI="http://www.mistrasgroup.com/role/ShareBasedCompensationCommonStockIssuedtoNonemployeeDirectorsDetails">
        <link:definition>0000072 - Disclosure - Share-Based Compensation - Common Stock Issued to Non-employee Directors (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareBasedCompensationRestrictedStockUnitAwardsOutstandingDetails" roleURI="http://www.mistrasgroup.com/role/ShareBasedCompensationRestrictedStockUnitAwardsOutstandingDetails">
        <link:definition>0000073 - Disclosure - Share-Based Compensation - Restricted Stock Unit Awards Outstanding (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareBasedCompensationPerformanceRestrictedStockUnitsNarrativeDetails" roleURI="http://www.mistrasgroup.com/role/ShareBasedCompensationPerformanceRestrictedStockUnitsNarrativeDetails">
        <link:definition>0000074 - Disclosure - Share-Based Compensation - Performance Restricted Stock Units Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ShareBasedCompensationPerformanceRestrictedStockUnitsActivityDetails" roleURI="http://www.mistrasgroup.com/role/ShareBasedCompensationPerformanceRestrictedStockUnitsActivityDetails">
        <link:definition>0000075 - Disclosure - Share-Based Compensation - Performance Restricted Stock Units Activity (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesIncomeLossBeforeProvisionforIncomeTaxesDetails" roleURI="http://www.mistrasgroup.com/role/IncomeTaxesIncomeLossBeforeProvisionforIncomeTaxesDetails">
        <link:definition>0000076 - Disclosure - Income Taxes - Income (Loss) Before Provision for Income Taxes (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesProvisionBenefitforIncomeTaxesDetails" roleURI="http://www.mistrasgroup.com/role/IncomeTaxesProvisionBenefitforIncomeTaxesDetails">
        <link:definition>0000077 - Disclosure - Income Taxes - Provision (Benefit) for Income Taxes (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesProvisionBenefitforIncomeTaxesComputedByApplyingStatutoryFederalTaxRateDetails" roleURI="http://www.mistrasgroup.com/role/IncomeTaxesProvisionBenefitforIncomeTaxesComputedByApplyingStatutoryFederalTaxRateDetails">
        <link:definition>0000078 - Disclosure - Income Taxes - Provision (Benefit) for Income Taxes Computed By Applying Statutory Federal Tax Rate (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesNarrativeDetails" roleURI="http://www.mistrasgroup.com/role/IncomeTaxesNarrativeDetails">
        <link:definition>0000079 - Disclosure - Income Taxes - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesDeferredIncomeTaxAssetsandLiabilitiesDetails" roleURI="http://www.mistrasgroup.com/role/IncomeTaxesDeferredIncomeTaxAssetsandLiabilitiesDetails">
        <link:definition>0000080 - Disclosure - Income Taxes - Deferred Income Tax Assets and Liabilities (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesChangesinUnrecognizedTaxBenefitsDetails" roleURI="http://www.mistrasgroup.com/role/IncomeTaxesChangesinUnrecognizedTaxBenefitsDetails">
        <link:definition>0000081 - Disclosure - Income Taxes - Changes in Unrecognized Tax Benefits (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitPlansDetails" roleURI="http://www.mistrasgroup.com/role/EmployeeBenefitPlansDetails">
        <link:definition>0000082 - Disclosure - Employee Benefit Plans (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RelatedPartyTransactionsDetails" roleURI="http://www.mistrasgroup.com/role/RelatedPartyTransactionsDetails">
        <link:definition>0000083 - Disclosure - Related Party Transactions (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeasesSupplementalBalanceSheetInformationDetails" roleURI="http://www.mistrasgroup.com/role/LeasesSupplementalBalanceSheetInformationDetails">
        <link:definition>0000084 - Disclosure - Leases - Supplemental Balance Sheet Information (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeasesNarrativeDetails" roleURI="http://www.mistrasgroup.com/role/LeasesNarrativeDetails">
        <link:definition>0000085 - Disclosure - Leases - Narrative (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeasesComponentsofLeaseCostsDetails" roleURI="http://www.mistrasgroup.com/role/LeasesComponentsofLeaseCostsDetails">
        <link:definition>0000086 - Disclosure - Leases - Components of Lease Costs (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeasesOtherInformationRelatedtoLeasesDetails" roleURI="http://www.mistrasgroup.com/role/LeasesOtherInformationRelatedtoLeasesDetails">
        <link:definition>0000087 - Disclosure - Leases - Other Information Related to Leases (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeasesMaturityofLeaseLiabilitiesDetails" roleURI="http://www.mistrasgroup.com/role/LeasesMaturityofLeaseLiabilitiesDetails">
        <link:definition>0000088 - Disclosure - Leases - Maturity of Lease Liabilities (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LeasesMaturityofLeaseLiabilitiesDetails_1" roleURI="http://www.mistrasgroup.com/role/LeasesMaturityofLeaseLiabilitiesDetails_1">
        <link:definition>0000088 - Disclosure - Leases - Maturity of Lease Liabilities (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CommitmentsandContingenciesDetails" roleURI="http://www.mistrasgroup.com/role/CommitmentsandContingenciesDetails">
        <link:definition>0000089 - Disclosure - Commitments and Contingencies (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SegmentDisclosureFinancialInformationDetails" roleURI="http://www.mistrasgroup.com/role/SegmentDisclosureFinancialInformationDetails">
        <link:definition>0000090 - Disclosure - Segment Disclosure - Financial Information (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SegmentDisclosureLonglivedAssetsbyGeographicAreaDetails" roleURI="http://www.mistrasgroup.com/role/SegmentDisclosureLonglivedAssetsbyGeographicAreaDetails">
        <link:definition>0000091 - Disclosure - Segment Disclosure - Long-lived Assets by Geographic Area (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SelectedQuarterlyFinancialInformationunauditedDetails" roleURI="http://www.mistrasgroup.com/role/SelectedQuarterlyFinancialInformationunauditedDetails">
        <link:definition>0000092 - Disclosure - Selected Quarterly Financial Information (unaudited) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
    </xs:appinfo>
  </xs:annotation>
  <xs:element id="mg_LimitedPartnershipMember" abstract="true" name="LimitedPartnershipMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_PaymentOfFinancingCostsOperatingActivities" abstract="false" name="PaymentOfFinancingCostsOperatingActivities" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_ClassActionOnBehalfOfCurrentAndFormerEmployeesMember" abstract="true" name="ClassActionOnBehalfOfCurrentAndFormerEmployeesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_IndustrialsMember" abstract="true" name="IndustrialsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_EffectiveIncomeTaxRateReconciliationDomesticNetOperatingLossCarrybackCARESActAmount" abstract="false" name="EffectiveIncomeTaxRateReconciliationDomesticNetOperatingLossCarrybackCARESActAmount" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_LongTermIncentivePlan2016Member" abstract="true" name="LongTermIncentivePlan2016Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_LitigationSettlementAmountAwardedFromOtherPartyNumberOfInstallments" abstract="false" name="LitigationSettlementAmountAwardedFromOtherPartyNumberOfInstallments" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:decimalItemType"/>
  <xs:element id="mg_DebtInstrumentCovenantComplianceTotalConsolidatedDebtLeverageRatio" abstract="false" name="DebtInstrumentCovenantComplianceTotalConsolidatedDebtLeverageRatio" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="mg_DefinedContributionPlanEmployersMatchingContributionAnnualVestingPeriod" abstract="false" name="DefinedContributionPlanEmployersMatchingContributionAnnualVestingPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mg_EuropeanReportingUnitMember" abstract="true" name="EuropeanReportingUnitMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_SeveranceandLaborDisputesMember" abstract="true" name="SeveranceandLaborDisputesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_PurchaseCommitmentCumulativeAmountCommitted" abstract="false" name="PurchaseCommitmentCumulativeAmountCommitted" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_OtherProcessIndustriesMember" abstract="true" name="OtherProcessIndustriesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_WeightedAverageDiscountRatePercentAbstract" abstract="true" name="WeightedAverageDiscountRatePercentAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="mg_PowerGenerationAndTransmissionMember" abstract="true" name="PowerGenerationAndTransmissionMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_CashFlowLesseeAbstract" abstract="true" name="CashFlowLesseeAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="mg_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareDueToNetLossDuringPeriodAmount" abstract="false" name="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareDueToNetLossDuringPeriodAmount" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="mg_VariousPipelineProjectsForTexasCustomerMember" abstract="true" name="VariousPipelineProjectsForTexasCustomerMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_SmallNDTServicesCompanyMember" abstract="true" name="SmallNDTServicesCompanyMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAverageSharePriceTradingPeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardAverageSharePriceTradingPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mg_DeferredIncomeTaxExpenseBenefitReserveForUncertainTaxPositions" abstract="false" name="DeferredIncomeTaxExpenseBenefitReserveForUncertainTaxPositions" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_InfrastructureResearchandEngineeringMember" abstract="true" name="InfrastructureResearchandEngineeringMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_DebtInstrumentCovenantConsolidatedDebtLeverageRatioMaximumMarginApplicableIfGreaterThan" abstract="false" name="DebtInstrumentCovenantConsolidatedDebtLeverageRatioMaximumMarginApplicableIfGreaterThan" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="mg_IncrementalCommonSharesAttributableToRestrictedStockUnitsOutstanding" abstract="false" name="IncrementalCommonSharesAttributableToRestrictedStockUnitsOutstanding" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="mg_AccruedWorkersCompensationAndHealthBenefitsCurrent" abstract="false" name="AccruedWorkersCompensationAndHealthBenefitsCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_OperatingLeasePercentageOfReductionOfRentalPayments" abstract="false" name="OperatingLeasePercentageOfReductionOfRentalPayments" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="mg_CreditAgreementMember" abstract="true" name="CreditAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_DebtCovenantPeriodThreeMember" abstract="true" name="DebtCovenantPeriodThreeMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_DebtInstrumentCovenantThresholdBusinessAcquisitionMinimumAmount" abstract="false" name="DebtInstrumentCovenantThresholdBusinessAcquisitionMinimumAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_AccruedSalariesWagesAndEmployeeRelatedBenefitsCurrent" abstract="false" name="AccruedSalariesWagesAndEmployeeRelatedBenefitsCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_DisposalOfForeignSubsidiariesMember" abstract="true" name="DisposalOfForeignSubsidiariesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityForeignCurrencyTranslationAdjustments" abstract="false" name="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityForeignCurrencyTranslationAdjustments" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_CurrentIncomeTaxExpenseBenefitReserveForUncertainTaxPositions" abstract="false" name="CurrentIncomeTaxExpenseBenefitReserveForUncertainTaxPositions" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_LossContingencyConsolidatedClaimsFiledNumber" abstract="false" name="LossContingencyConsolidatedClaimsFiledNumber" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="mg_ClassActionOnBehalfOfStateOfCaliforniaMember" abstract="true" name="ClassActionOnBehalfOfStateOfCaliforniaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_TexasCustomerMember" abstract="true" name="TexasCustomerMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_ClassActionMember" abstract="true" name="ClassActionMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_RestrictedStockUnitsRSUsandPerformanceStockUnitsPSUsMember" abstract="true" name="RestrictedStockUnitsRSUsandPerformanceStockUnitsPSUsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_OtherLongTermDebtMember" abstract="true" name="OtherLongTermDebtMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_DefinedContributionPlanMinimumAgeForEmployeesToContributeCatchUpContributionsUnderInternalRevenueServicesLimits" abstract="false" name="DefinedContributionPlanMinimumAgeForEmployeesToContributeCatchUpContributionsUnderInternalRevenueServicesLimits" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mg_WeightedAverageRemainingLeaseTermAbstract" abstract="true" name="WeightedAverageRemainingLeaseTermAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="mg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfNonEmployeeDirectorsToWhomAwardIsGranted" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfNonEmployeeDirectorsToWhomAwardIsGranted" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="mg_AccruedLiabilitiesDeferredRevenuesAndContingentConsiderationLiabilitiesCurrent" abstract="false" name="AccruedLiabilitiesDeferredRevenuesAndContingentConsiderationLiabilitiesCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_AccruedExpensesAndOtherLiabilitiesCurrent" abstract="false" name="AccruedExpensesAndOtherLiabilitiesCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_PaymentsToAcquireIntangibleAssetsAndSoftware" abstract="false" name="PaymentsToAcquireIntangibleAssetsAndSoftware" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_AcquisitionRelatedCostsAndFairValueAdjustmentsToInitialPurchasePriceAllocation" abstract="false" name="AcquisitionRelatedCostsAndFairValueAdjustmentsToInitialPurchasePriceAllocation" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_ForeignTaxCutsAndJobsActChangeInTaxRateIncomeTaxExpenseBenefit" abstract="false" name="ForeignTaxCutsAndJobsActChangeInTaxRateIncomeTaxExpenseBenefit" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIncreaseDecreaseDueToChangesInAmount" abstract="false" name="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIncreaseDecreaseDueToChangesInAmount" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_ServicesMember" abstract="true" name="ServicesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityAccretion" abstract="false" name="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityAccretion" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_PetrochemicalMember" abstract="true" name="PetrochemicalMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_SelfInsurancePolicyTextBlock" abstract="false" name="SelfInsurancePolicyTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="mg_VariableRateComponentAxis" abstract="true" name="VariableRateComponentAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="mg_AssetsAndLiabilitiesLesseeTableTextBlock" abstract="false" name="AssetsAndLiabilitiesLesseeTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="mg_TaxCutsAndJobsActTransitionTaxForAccumulatedForeignEarningsLiability" abstract="false" name="TaxCutsAndJobsActTransitionTaxForAccumulatedForeignEarningsLiability" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_CanadianTaxAuthorityProvinceOfAlbertaMember" abstract="true" name="CanadianTaxAuthorityProvinceOfAlbertaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_ContingentConsiderationMember" abstract="true" name="ContingentConsiderationMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_ProductsandSystemsMember" abstract="true" name="ProductsandSystemsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_DeferredTaxAssetsInterestCarryforwards" abstract="false" name="DeferredTaxAssetsInterestCarryforwards" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_ConsultingServicesMember" abstract="true" name="ConsultingServicesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_RevenuePracticalExpedientIncrementalCostOfObtainingContractMaximumPeriod" abstract="false" name="RevenuePracticalExpedientIncrementalCostOfObtainingContractMaximumPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mg_AuditInformationAbstract" abstract="true" name="AuditInformationAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="mg_IncrementalCommonSharesAttributableToStockOptionsOutstanding" abstract="false" name="IncrementalCommonSharesAttributableToStockOptionsOutstanding" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="mg_EmployeeStockOwnershipPlanNumberOfPlans" abstract="false" name="EmployeeStockOwnershipPlanNumberOfPlans" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="mg_VariableRateComponentMember" abstract="true" name="VariableRateComponentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_TheCreditAgreementJPMorganChaseBankMember" abstract="true" name="TheCreditAgreementJPMorganChaseBankMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_EffectiveIncomeTaxRateReconciliationRepatriationOfForeignEarningsChangeDueToChangeInTaxRateAmount" abstract="false" name="EffectiveIncomeTaxRateReconciliationRepatriationOfForeignEarningsChangeDueToChangeInTaxRateAmount" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_DebtCovenantPeriodDomain" abstract="true" name="DebtCovenantPeriodDomain" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_OilGasMember" abstract="true" name="OilGasMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_IncreaseDecreaseInOtherAccruedLiabilitiesAndDeferredLiabilities" abstract="false" name="IncreaseDecreaseInOtherAccruedLiabilitiesAndDeferredLiabilities" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_NumberOfDirectors" abstract="false" name="NumberOfDirectors" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="mg_AcquisitionRelatedContingenciesMember" abstract="true" name="AcquisitionRelatedContingenciesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_AerospaceandDefenseMember" abstract="true" name="AerospaceandDefenseMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_DeferredIncomeTaxExpenseBenefitNet" abstract="false" name="DeferredIncomeTaxExpenseBenefitNet" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_OtherAmericasMember" abstract="true" name="OtherAmericasMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_LitigationSettlementAmountAwardedFromOtherPartyInstallmentPercentage" abstract="false" name="LitigationSettlementAmountAwardedFromOtherPartyInstallmentPercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="mg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsPerformanceConditionAdjustmentsNet" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsPerformanceConditionAdjustmentsNet" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="mg_CorporateAndEliminationsMember" abstract="true" name="CorporateAndEliminationsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_LineOfCreditFacilityMaximumBorrowingCapacityAvailableForIssuanceOfLettersOfCredit" abstract="false" name="LineOfCreditFacilityMaximumBorrowingCapacityAvailableForIssuanceOfLettersOfCredit" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_ExecutiveAndSeniorOfficersMember" abstract="true" name="ExecutiveAndSeniorOfficersMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_DefinedContributionPlanContinuousServicePeriodAfterWhichEmployeesBecomeEligibleToParticipateUnderPlan" abstract="false" name="DefinedContributionPlanContinuousServicePeriodAfterWhichEmployeesBecomeEligibleToParticipateUnderPlan" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mg_DebtInstrumentCovenantFixedChargeCoverageRatio" abstract="false" name="DebtInstrumentCovenantFixedChargeCoverageRatio" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="mg_EffectiveIncomeTaxRateReconciliationRepatriationOfForeignEarningsChangeDueToChangeInTaxRatePercent" abstract="false" name="EffectiveIncomeTaxRateReconciliationRepatriationOfForeignEarningsChangeDueToChangeInTaxRatePercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="mg_DeferredTaxAssetsOperatingLeaseLiabilities" abstract="false" name="DeferredTaxAssetsOperatingLeaseLiabilities" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsPerformanceConditionAdjustmentsNetWeightedAverageGrantDateFairValue" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsPerformanceConditionAdjustmentsNetWeightedAverageGrantDateFairValue" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="mg_LossContingencyNumberOfWeldsInspected" abstract="false" name="LossContingencyNumberOfWeldsInspected" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="mg_DebtInstrumentCovenantConsolidatedDebtLeverageRatioLowestAvailableMarginApplicable" abstract="false" name="DebtInstrumentCovenantConsolidatedDebtLeverageRatioLowestAvailableMarginApplicable" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="mg_RightOfUseAssetObtainedInExchangeForLeaseLiabilityAbstract" abstract="true" name="RightOfUseAssetObtainedInExchangeForLeaseLiabilityAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="mg_DebtCovenantPeriodFourMember" abstract="true" name="DebtCovenantPeriodFourMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_BrazilianReportingUnitMember" abstract="true" name="BrazilianReportingUnitMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_LineOfCreditFacilityMaximumBorrowingCapacityInNonUSCurrencies" abstract="false" name="LineOfCreditFacilityMaximumBorrowingCapacityInNonUSCurrencies" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_COVID19PandemicMember" abstract="true" name="COVID19PandemicMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_LongTermIncentivePlan2009Member" abstract="true" name="LongTermIncentivePlan2009Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_CapitalManagementEnterpriseCMEMember" abstract="true" name="CapitalManagementEnterpriseCMEMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_VariableRateComponentDomain" abstract="true" name="VariableRateComponentDomain" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_LossContingencyNumberOfWeldsAllegedNotInCompliance" abstract="false" name="LossContingencyNumberOfWeldsAllegedNotInCompliance" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="mg_DebtCovenantPeriodTwoMember" abstract="true" name="DebtCovenantPeriodTwoMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_LongTermPurchaseCommitmentExtensionPeriod" abstract="false" name="LongTermPurchaseCommitmentExtensionPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardPerformancePeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardPerformancePeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mg_ProceedsFromIncomeTaxRefundsCARESAct" abstract="false" name="ProceedsFromIncomeTaxRefundsCARESAct" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_DeferredTaxAssetsFinanceLeaseObligation" abstract="false" name="DeferredTaxAssetsFinanceLeaseObligation" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_DebtCovenantPeriodAxis" abstract="true" name="DebtCovenantPeriodAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="mg_DebtInstrumentCovenantNumberOfDaysBeforeBusinessAcquisitionWrittenNoticeRequired" abstract="false" name="DebtInstrumentCovenantNumberOfDaysBeforeBusinessAcquisitionWrittenNoticeRequired" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mg_OperatingLeaseArrangementMember" abstract="true" name="OperatingLeaseArrangementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_ShareBasedCompensationArrangementByShareBasedPaymentAwardLastDayTradingPeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardLastDayTradingPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mg_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerformanceConditionAdjustmentsIncrease" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardPerformanceConditionAdjustmentsIncrease" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="mg_TermALoanFacilityMember" abstract="true" name="TermALoanFacilityMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_OtherProductsandServicesMember" abstract="true" name="OtherProductsandServicesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_MinimumAmountOfWorkersCompensationAndHealthBenefitClaimsForWhichThirdPartyExcessInsuranceCoverageMaintained" abstract="false" name="MinimumAmountOfWorkersCompensationAndHealthBenefitClaimsForWhichThirdPartyExcessInsuranceCoverageMaintained" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_DebtCovenantPeriodOneMember" abstract="true" name="DebtCovenantPeriodOneMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_DeferredIncomeTaxNoncashExpenseBenefit" abstract="false" name="DeferredIncomeTaxNoncashExpenseBenefit" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_EffectiveIncomeTaxRateReconciliationDomesticNetOperatingLossCarrybackCARESActPercent" abstract="false" name="EffectiveIncomeTaxRateReconciliationDomesticNetOperatingLossCarrybackCARESActPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="mg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAwardMetrics" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAwardMetrics" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="mg_OfficeFurnitureAndEquipmentMember" abstract="true" name="OfficeFurnitureAndEquipmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_MultiemployerPlanPensionSignificantFundedStatusPercentage" abstract="false" name="MultiemployerPlanPensionSignificantFundedStatusPercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="mg_ScheduleOfBusinessCombinationAcquisitionRelatedCostsTableTextBlock" abstract="false" name="ScheduleOfBusinessCombinationAcquisitionRelatedCostsTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="mg_BoilermakersandPipefittersPlansMember" abstract="true" name="BoilermakersandPipefittersPlansMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_AccruedLiabilitiesDeferredRevenuesAndContingentConsiderationLiabilitiesCurrentDisclosureTextBlock" abstract="false" name="AccruedLiabilitiesDeferredRevenuesAndContingentConsiderationLiabilitiesCurrentDisclosureTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="mg_InternationalMember" abstract="true" name="InternationalMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_ScheduleOfAccruedLiabilitiesDeferredRevenueAndContingentConsiderationLiabilitiesCurrentTableTextBlock" abstract="false" name="ScheduleOfAccruedLiabilitiesDeferredRevenueAndContingentConsiderationLiabilitiesCurrentTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="mg_DebtCovenantPeriodFiveMember" abstract="true" name="DebtCovenantPeriodFiveMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_PaymentsOfContingentConsiderationForBusinessAcquisitions" abstract="false" name="PaymentsOfContingentConsiderationForBusinessAcquisitions" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_RightToCustomerContractsMember" abstract="true" name="RightToCustomerContractsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
</xs:schema>
