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  <xs:element id="mg_DebtCovenantPeriodNineMember" abstract="true" name="DebtCovenantPeriodNineMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="mg_IndustrialsMember" abstract="true" name="IndustrialsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="mg_OperatingLeaseArrangementMember" abstract="true" name="OperatingLeaseArrangementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="mg_DebtInstrumentCovenantMinimumEBITDAAmount" abstract="false" name="DebtInstrumentCovenantMinimumEBITDAAmount" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_OilGasMember" abstract="true" name="OilGasMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum: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_DebtCovenantPeriodSixMember" abstract="true" name="DebtCovenantPeriodSixMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="mg_DebtInstrumentCovenantPrepaymentOfOutstandingCreditFacilityRequiredIfCashAndCashEquivalentsExceedsAmount" abstract="false" name="DebtInstrumentCovenantPrepaymentOfOutstandingCreditFacilityRequiredIfCashAndCashEquivalentsExceedsAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_DefinedContributionPlanMinimumAgeForEmployeesToContributeCatchUpContributionsUnderIRSLimits" abstract="false" name="DefinedContributionPlanMinimumAgeForEmployeesToContributeCatchUpContributionsUnderIRSLimits" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <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_RestrictedStockUnitsRSUsandPerformanceStockUnitsPSUsMember" abstract="true" name="RestrictedStockUnitsRSUsandPerformanceStockUnitsPSUsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <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_DebtCovenantPeriodSevenMember" abstract="true" name="DebtCovenantPeriodSevenMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="mg_OperatingLeaseDeferralPeriodOfRentalPayments" abstract="false" name="OperatingLeaseDeferralPeriodOfRentalPayments" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mg_AssetsAndLiabilitiesLesseeTableTextBlock" abstract="false" name="AssetsAndLiabilitiesLesseeTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType"/>
  <xs:element id="mg_LossContingencyNumberOfWeldsInspected" abstract="false" name="LossContingencyNumberOfWeldsInspected" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <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_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalAwardsMetrics" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalAwardsMetrics" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
</xs:schema>
