Dear Mr. Masthan,
Materials properties enhanced by tempering, means that materials heat treated with Narmalized + Tempered or Quenched + Tempered to retain specific properties (increased toughness with loss in strength) after tempering operation. Also note that these materials if required for PWHT, the PWHT temperature shall be below the tempering temperature in order to retain the properties enhanced by tempering operation. To some extent it will help to reduce HIC cracking problems.
You need to ensure the tempering temperature from the material manufacturer and PWHT temperature shall be selected accordingly. As per ASME Sec. IX, QW-407.2, PWHT time at temperature shall be considered as essential variables when impact test is required by other code sections. Hence PWHT cycle time is essential variable, in order to accommodate any repair after PWHT. In general all PQR test coupon shall be required to undergo two to three heat treatment cycle to take care repair.
Heat treatment cycle (time at temperature) increases there may a change to reduce the toughness of weld metal since prolonged time at PWHT temperature. At the same time hardness may improve.
Regards,
L. Prabhu kumar,
Sr. Principal Engineer,
Equipments & Materials Dept.,
Saipem India Projects Limited,
Tel:+91 44 43906588, Ext.: 588, Fax:+91 44 66840345,
Mobile Ph. No.: +91 9003010978.
From:
Sent: Saturday, June 19, 2010 11:52 PM
To:
Subject: [MW:5659] SIMULATED PWHT FOR THE MATERIALS
We are manufacturer of pressure vessels and one of the major client specifications explains about the simulated heat treatment of material as under
“Materials with properties enhanced by heat treatment cycles such as tempering, intermediate stress relief (ISR) and the final post weld heat treatment shall be tested to verify that their mechanical properties have been retained after all heat treatment cycles. These tests shall also include two additional post weld heat treatment cycles to account for future repairs or alteration.”
Query: 1: My understanding is that the above paragraph is referring only to the materials for shells & heads of the equipment.
Query: 2: My understanding is that the above paragraph is referring only to the material undergoing PWHT in order to achieve certain properties like HIC resistance etc. (or) some specific metals which mechanical properties may enhance due to PWHT not due to thickness for PWHT (ie 38 mm above as per UCS-56).In this case, combined three cycles of SPWHT will fully satisfy the above paragraph requirement.
Query: 3: If for the above queries (1 & 2), suppose my understanding is not correct, Please check the below condition for the applicability of
For example
· Dish Head/Toricone of the pressure vessel requires Stress Relieving due to exceeding the allowable fiber elongation as specified in UCS-79(d)
· Instead of heat treating separate petals of the dish head / toricone, the dish head/toricone petals are welded and also shell portions are welded to it. The complete assembly is then heat treated to relieve residual stresses of Dish head / toricone. (This is done to avoid any distortion caused during Stress relieving of separate petals of the dish head / toricone)
· In this case, with reference to above
Please note due to some reason, we are not clarifying the above directly with client. I need opinion from experts.
Regards
M.M
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