2 replies to this topic

[cea]

Dear All-

I am working on Gas oil Hydrotreater project, wherein I am required to identify lines that shall have PWHT (post weld heat treatment).

As per my understanding, PWHT is applicable when
1) NACE requirement due to sulphide stress cracking region by wet H2S (based on partial pressure of H2S with respect to pressure)
2) Hydrogen service where pressure is more than 200 barg
3) In case of plate thickness is more than or equal to 32 mm.

Kindly indicate whether my information is correct. Kindly update me in case of any change.

My main interest is for H2 service requirement.

Thanks in advance & Regards

[marthin_was]

You should consult to ANSI B31.3 for complete information.

PWHT is required for relieving residual stress created due to un-event heat distribution in thick plates. You are right also that by doing PWHT you will eliminate induced H2S cracking.

PWHT is important issue that need to take care seriously, because I found many cases that pipe of pressure vessel failed due to residual stress. That's why I strongly recommend you to consult with your piping engineer, ANSI b31.3 is a good start to understand about this topic.

Dear All-

I am working on Gas oil Hydrotreater project, wherein I am required to identify lines that shall have PWHT (post weld heat treatment).

As per my understanding, PWHT is applicable when
1) NACE requirement due to sulphide stress cracking region by wet H2S (based on partial pressure of H2S with respect to pressure)
2) Hydrogen service where pressure is more than 200 barg
3) In case of plate thickness is more than or equal to 32 mm.

Kindly indicate whether my information is correct. Kindly update me in case of any change.

My main interest is for H2 service requirement.

Thanks in advance & Regards

[Qalander (Chem)]

You should consult to ANSI B31.3 for complete information.

PWHT is required for relieving residual stress created due to un-event heat distribution in thick plates. You are right also that by doing PWHT you will eliminate induced H2S cracking.

PWHT is important issue that need to take care seriously, because I found many cases that pipe of pressure vessel failed due to residual stress. That's why I strongly recommend you to consult with your piping engineer, ANSI b31.3 is a good start to understand about this topic.

Dear All-

I am working on Gas oil Hydrotreater project, wherein I am required to identify lines that shall have PWHT (post weld heat treatment).

As per my understanding, PWHT is applicable when
1) NACE requirement due to sulphide stress cracking region by wet H2S (based on partial pressure of H2S with respect to pressure)
2) Hydrogen service where pressure is more than 200 barg
3) In case of plate thickness is more than or equal to 32 mm.

Kindly indicate whether my information is correct. Kindly update me in case of any change.

My main interest is for H2 service requirement.

Thanks in advance & Regards

Dear cea Hello/Good Evening,
Although you and 'marthin_was' may be right,
but I have always considered the PWHT requirements related to Heating the area of 'weld& close vicinity parent metal welded joining' to have the

'lattice structure' restored through gradual heating up to a pre-determined, recommended temperature, then gradual cooling down thereby ensuring all properties of chemical resistance, tensile strength etc. as close as possible to the original parent metal.

As regards thickness of parent metal dictating the needs; someone more knowledgeable to comment.
Since usually this is taken care through edges preparation allowing sufficient weld penetrations into joining of concerned parent metal surface if needed from either side (outer& inner)

However for quite a few Alloy steels do positively need PWHT I believe to regain lattice structure alone.
Hope this helps in way forward!