B31.3 Pipe Shoe Stress Relieving 1

[dsphillips]

I have been approached as to whether it is necessary to stress relieve pipe shoes that are welded to the pipe as attachments. Per 31.3, it is not necessary with the thickness of materials that we are using. But our corporate standard does require ALL welds in sour service to be stress relieved.

I was wondering what the pros and cons of stress relieving the attachment welds are. The materials are all P-1. Thanks for the input.

 

[aurrous]

If it is a regular lets say sa 106 gr b carbon steel pipe. (p1) And you do have a thickness of less than .75 inches, then normally the weld dose not have to be PWHT. However, if your WPS says you have to PWHT P1 materials, then unfortunatly you have to post weld heat treat the materials. You have to follow the welding procedure, you welded the material too.
What are the benifits? you pwht the pipe to realign the molicules, you take some of the minor stresses out, you increase the life of the part, (slightly), and you change its redox (oxidation/reduction) rate slighty compaired to the unPWHT part. Basicly you get rid of all the misaligned molicules in the HAZ and make it a slightly stronger part than the un PWHT weld. Normally the only times you might think of PWHT a regular carbon weld ( lets say .250" thick and 3" id) would be if you had 2(.5" appart) welds side by side, which caused 2 over lapping or close HAZ.
The metal in the dual zones would be over baked, embrittled, and stressed out. Soo you PWHT get it back to normal and get on with your life. Normally however this change is very small, instead of maybe 30 years you might get like 29 out of the part. It really hard to say why they wanted the PWHT but if your WPS,PQR, say its needs it, it gets it. IF its a type o' have it changed, or put in a clause saying when needed.
hope that helps.

 

[bmoorthy]

Check MR0175 Which gives guidelines and explanations for Sour service requirements.
PWHT as Service requirements are basically from past experience and are generally given in a more stringent form. It takes more severe connotation when such requirements are provided in General Spec or Corporate Manual/Spec. Generally specifications themselves are to be specific to job, thereby being objective.

Even in case of Pressure vessels UCS 56 (Section VIII Div 1)Notes gives sufficient relief for this kind of situation.
Although your guiding code could be different,In this case, i think it is not mandatory, so long as suitable preheat is followed.

As regards WPS/PQR, you may qualify separate PQR and revise your WPS.

For Sour service as per NACE MR0175, Hardness of Weld and HAZ shall be less than 200 BHN.