AA 085 01 50CORPORATE STANDARD Rev. No. 00 PAGE 1 OF 4 Residual Stress Measurement on Turbine and Generator shafts 1. Residual Stress Condition In the Course of heat treatment processes of turbine and generator shafts compressive residual stresses are induced in near surface areas. They are matched by tensile residual stresses in the n i terior. As turbine and generator shafts always undergo operational tensile stress, the residual stresses remaining after the heat treatment process are unfavorable. Therefore try to reduce residual Stresses as far as possible. The Information on this document is the property of BHARAT HEAVY ELECTRICALS LIMITED It must not be used directly or Indirectly in any way detrimental to the Interest of the company. BHEL delivery specifications do not define the cooling down rates from tempering temperature conditions. lnstead of this it has been specified that the compressive residual stresses must not exceed 60 N/mm2 at any place on the surface. This has to be proved by Residual Stress Measurements performed by the manufacturer. 2. Residual Stress measurements 2.1 Residual Stress measurements are to be performed by the ring-core-method. To assure COPYRIGHT AND CONFIDENTIAL a conforming assessment of the results by the manufacturer and BHEL, the residual Stresses have to be calculated for the depth region from 2 to 4 mm using following formulas: ε tan (2mm) - ε tan (4mm) ε ax (2mm) - ε ax (4mm) σ tan = -------------------------------- + ---------------------------------- 2.36 11.2 ε ax (2mm) - ε ax (4mm) ε tan (2mm) - ε tan (4mm) σ ax = -------------------------------- + ---------------------------------- 2.36 11.2 These formulas are valid for 26NiCrMoV 145 and ring core of 14 mm in diameter. Stresses (σ) are given in N/mm², strains (ε) in µm/m. 2.2 Stress measurements have to be performed after the last tempering treatment on the contour as tempered. The appropriate location of the three measuring Points are marked in annex 1 and 2. Measurements have to be performed at the Points specified, being offset by 120° on circumference. Revisions : APPROVED : INTERPLANT MATERIAL RATIONALISATION Cl. 33.1.0 of MOM of FC&F+HTM COMMITTEE-MRC (FCF+HTM) Rev. No. 00 Amd.No. Reaffirmed: Prepared Issued Dt. of 1st. Issue Dt: Dt : Year : HARIDWAR Corp. R&D FEB. 2008 AA 085 01 50 Rev.4 Repeat the Stress measurernents. if re-heat treatment or re-tempering is required. 00 CORPORATE STANDARD PAGE 2 OF 4 2. the relevant Stress condition cannot be determined unambiguously. . No. contact BHEL in any case to ensure that the cutting allowance available will suffice. 2.6 An immediate and close exchange of experience regarding the measured values between manufacturer and BHEL is necessary. Should the occasion arise.3 If measurements are to be performed on the contour as delivered. certain locations can be specified by BHEL.5 In case. BHEL reserves the right to define additional measuring Points. 2. 2. AA 085 01 50 CORPORATE STANDARD Rev. Order no. Identification no: Subject Material: Heat treatment Residual stress measurement Test method: ring-core-method Heat treatment contour Delivery contour Test position 1 2 3 1 2 3 Reference point Time pos. 00 PAGE 3 OF 4 Annexure-1 Customer Drawing no. . No. specification N/mm″ σ tg N/mm″ σ ax N/mm″ Date Company Dept. No. Identification no: Subject Material: Heat treatment Residual stress measurement Test method: ring-core-method Heat treatment contour Delivery contour Test position 1 2 3 1 2 3 Reference point Time pos. Order no. specification N/mm″ σ tg N/mm″ σ ax N/mm″ Date Company Dept.AA 085 01 50 Rev. . 00 CORPORATE STANDARD PAGE 4 OF 4 Annexure-2 Customer Drawing no.
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