PWHT of carbon steel in H2S environment

Date 01-23-2005 13:01

Dear all
WE have many Air coolers in our refinery so that now we want repair a header box of them by welding.The material of header is carbon steel with 15mm thickness and inside fluid in header has H2S and operating pressure is 5 Barg.Do we need PWHT after welding?(area of welding is a circle with 1" diameter)I saw in ASME that carbon steel in sour water and caustic service need to PWHT.what about a fluid with H2S?why?
best regards
A.Sharif

By chall

Date 01-25-2005 14:01

To answer this properly there are several considerations:

(1) What is the construction code used to fabricate this component?

(2) Does NACE 0175 apply?

(3) Does the owner have specific requirements? Many times it doesn't matter what the code requirements are, the owner may have more stringent requirements. We run into this situation often in chemical plants.

Charles Hall.

By jon20013 (*****)

Date 01-25-2005 18:24

Without a doubt NACE MR0175 applies. In the simplest of terms, hydrogen sulfide is extraordinairly corrosive, flammable and can create a hazard to human life in very small quantities. My best guess without pulling the books down is PWHT is to help enhance properties against corrosive effects of the H2S.

By chall

Date 01-25-2005 19:15

My 0175 is dated 2002, so this info may be dated. My understanding is that as long as the post weld hardness (including the HAZ) does not exceed 22 HRC, PWHT is not required. Generally welded carbon steel will not exceed 22HRC.

That said, many owners simply require PWHT to reduce the liklihood of SSC.

Charles Hall

By jon20013 (*****)

Date 01-25-2005 19:35

This is a pure and simple guess here but, the baseline construction code is probably ASME B31.3 with NACE MR0175 invoked as a separate but parallel standard. I've just had my first experience with MR0175 recently and have to say it's not nearly so "user friendly" as the older API counterpart!