PWHT for caustic soda pipe
PWHT for caustic soda pipe
(OP)
Hi,
I have the following problem. We have a 2" carbon steel pipe for caustic soda (50%)for which our customer(Refinery)requires a PWHT. The question is whether or not it is techically necessary to carry out this test since it is not required by ASME B31.3. We believe that the pipe will not suffer from corrosion if the PWHT is not carried out.
Thanks,
I have the following problem. We have a 2" carbon steel pipe for caustic soda (50%)for which our customer(Refinery)requires a PWHT. The question is whether or not it is techically necessary to carry out this test since it is not required by ASME B31.3. We believe that the pipe will not suffer from corrosion if the PWHT is not carried out.
Thanks,





RE: PWHT for caustic soda pipe
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RE: PWHT for caustic soda pipe
You wrote "The question is whether or not it is techically necessary to carry out this test "
The PWHT is not a test. PWHT is Post Weld Heat Treat.
As in put it in an oven and heat it up to (a high temperature) and let it cool at a controlled rate.
You may want to check with someone with NACE (National Association of Corrosion Engineers) for criteria for welding on Caustic lines.
RE: PWHT for caustic soda pipe
RE: PWHT for caustic soda pipe
If it below 120F, you should have no problem.
The additional cost requirement of the PWHT would be better spent on a thicker pipe... (Sched 80 ?)
-MJC
RE: PWHT for caustic soda pipe
If your client (that would be the folks who are operating the refinery and on the receiving end of the explosion / caustic spray) states that the PWHT is required for process / materials reasons then it would be extremely poor engineering judgement to take the position that "the code doesn't require PWHT so we won't spend the money doing it." Engineers need to produce reliable designs, not just follow the minimum requirements of codes.
Caustic cracking is real. It causes real failures. Failures cost more than doing it right the first time.
jt
RE: PWHT for caustic soda pipe
We have an extensive NaOH distribution system encompassing 50% to 1% and our requirement is that All piping will undergo PWHT with no exceptions. Even with the PWHT were are careful about the routing of these lines for people protection.
Part of our process produces Amines and Imines where again all the piping has to have PWHT though not required by code.
RE: PWHT for caustic soda pipe
As unclesyd mentions, refinery applies this to all pipes regardless of sch, but ASME specifies this treatment only for certain schedules.
RE: PWHT for caustic soda pipe
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdoweb/
RE: PWHT for caustic soda pipe
I thought that I had some good (although old) references ( including the ancient PPG guidelines)regarding system design of 50% caustic soda systems.
Caustic cracking is a concern at 50% solution, but according to my recollection, its only when the operating temperature is >120F. PPG also recommends SCH 80 piping
While I do not doubt your experience, I am looking for an industry guideline/ white paper that endorses the PWHT of ALL PIPING JOINTS....
Is there something out there more authoritative than the API 571 note ?
What about CS welded tank construction ?
Is PWHT required there also ?
-MJC
RE: PWHT for caustic soda pipe
Right On!
RE: PWHT for caustic soda pipe
And, on a side note, if the customer said do it.....and they're paying for it....(as long as it was in the contract, else send them a change order request).
RE: PWHT for caustic soda pipe
RE: PWHT for caustic soda pipe
Please note that under 300 (b)(1)of B31.3 the Owner has overall resposibility for the design, construction, testing, etc. of the piping system. The Owner is responsible for the corrosion design requirements including provisions to mitigate stress corrosion cracking in service.
RE: PWHT for caustic soda pipe
RE: PWHT for caustic soda pipe