Do all Carbon Steel piping systems require PWHT for service in H2S?

Asked by keler01 6 years ago | 1 Answers

1 Answer

phamus 6 years ago

All equipment and piping in carbon and low alloy steel should be subject to a post weld heat treatment (PWHT). PWHT for piping should comply with the requirements of ASME B31.3 and NACE MR0175 / ISO 15156.

In order to avoid the PWHT requirement on a piping system, all the following requirements should be satisfied (this is only applicable to Carbon Steels):

Thickness should be below the limit for which the code requires PWHT.
Maximum carbon content should be 0.23%.
Maximum carbon equivalent should be 0.43%.
SMYS should be equal or less than 360 MPa (52 ksi).
The weld procedure should be qualified with a maximum allowable hardness in the survey of 248 HV10.
The material in the final fabricated form must meet the hardness requirements.
Piping must be seamless. Welded pipe can be considered on a case by case basis.

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