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And see also the text bellow from Nace SP0472-2010
Section 3: Prevention of Alkaline Stress Corrosion Cracking
3.1 PWHT shall be used to reduce residual stresses when prevention of ASCC is specified by the user. In services
where both ASCC and HSC/SSC are concerns, weldment hardness controls shall be applied in addition to PWHT.
3.2 ASME Boiler and Pressure Vessel Code, Section VIII, allows PWHT to be performed at lower than the normally
specified temperature if it is held for a longer time. However, when PWHT is being performed for prevention of
ASCC, these lower temperatures shall not be used.
3.3 For amine and caustic cracking services, an effective PWHT procedure shall consist of heating weldments to
635 ± 15 °C (1,175 ± 25 °F) for a hold time of one hour for each 25 mm (1.0 in), or a fraction thereof, of metal
thickness, with a minimum hold time of one hour.
3.3.1 When PWHT is used for ASCC, the requirements for HAZ hardness control for SSC as defined in
Paragraph 2.3 also must be considered for services exposed to both SSC and ASCC. The allowable variation in
the chemical composition of steels could be considerable, even within the same grade. In conjunction with
welding variables, this can produce high hardness in HAZs that might not be adequately softened by this
specified thermal stress relief. Each situation should be evaluated to determine whether this thermal stress relief
is adequate.
3.4 For carbonate cracking services, an enhanced stress-relieving heat treatment should be used. The heat
treatment temperature should be 649 to 663 °C (1,200 to 1,225 °F) for a hold time of one hour for each 25 mm (1.0
in) of thickness, with a minimum hold time of one hour.
3.4.1 In addition to the higher heat treatment temperature, the guidelines provided in Paragraph 5.2.3.1 of API
RP 945 and AWS D10.1031 should be incorporated into the heat treatment procedures to minimize the residual
stresses that remain after the stress-relieving heat treatment.
3.5 When heat treatment is used to prevent ASCC, all welds and weld heat-affected areas shall receive PWHT,
including all pressure-containing welds, seal welds, internal attachment welds, nozzle-reinforcing pad welds,
temporary fabrication attachment welds, and arc strikes.
3.5.1 External attachment welds often generate residual stresses extending through the entire wall thickness.
If they do, they shall also receive PWHT. Only if an evaluation shows that the residual stresses do not extend
through wall may PWHT be considered optional.
3.6 Experience has shown that heating bands wider than required by codes (approximately > 250 mm [10 in]) are
sometimes necessary. This applies primarily to weldments in large-diameter (> 250 mm [10 in]) piping.
3.7 After PWHT, actions that reintroduce high residual stresses, such as straightening, should be avoided. If these
actions have been done, a second PWHT should be performed when deemed necessary by the user.
3.8 The shot peening process should not be used for applications in ASCC environments as a substitute for PWHT.
3.9 Alternative welding methods such as temper bead welding and controlled-deposition welding shall not be used
for prevention of ASCC.
3.10 During original fabrication, weldments should be inspected for defects such as lack of fusion, delayed
hydrogen cracking, or severe undercut. Any defects found should be removed.