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When is PWHT necessary - according to the standards?
4

When is PWHT necessary - according to the standards?

When is PWHT necessary - according to the standards?

(OP)
Looking for a document (preferably a standard or something with authority) that states under what conditions PWHT is necessary.
I'm not looking for experience or guidelines to be clear, I'm looking for codes or standards that states when PWHT is (or is not) necessary.

Probably 90% of our activities fall under ISO standards, but I haven't found anything there.
However, steel doesn't know if it's being welded in Europe, USA or anywhere else. So I'll take whatever references you might have.

FYI, ISO/TR 14745 (PWHT parameters) says:
This Technical Report does not specify when PWHT is required. Such requirements are given in product
standards, material specifications, or material data sheets.
That's the closest thing I have found.

No product standards or material specs under EN/ISO however gives this information - or I haven't been looking deep enough into it. All help or guidance is welcome!

RE: When is PWHT necessary - according to the standards?

Kingnero,

How familiar are you with ASME codes and specs? PWHT requirements are spelled out quite well in all of them.

The devil is in the details; she also wears prada.

RE: When is PWHT necessary - according to the standards?

Kingnero,
AS DVWE has noted ASME (piping & vessels) and AWS (structural) codes / standards have extensive requirements for PWHT noted.
Try this one to start
ASME B31 P
This Standard provides requirements for heat treatment of piping assemblies that meet the requirements of ASME B31 Code Sections. These requirements apply to: preheating; postweld heat treatment (PWHT); postforming heat treatment (PFHT) required by the ASME B31 Code Sections for other fabrication processes, including forming processes such as bending; and heat treatments required by contract specifications.

RE: When is PWHT necessary - according to the standards?

AWS D1.1 Structural Welding code includes an Annex that provides an "alternate" means of determining preheat for carbon and low alloy steels common to steel framed buildings. It takes into consideration the carbon equivalent, thickness, and degree of restraint. It is fairly conservative compared to ASME and other standards where the degree of restraint is low.

Best regards - Al

RE: When is PWHT necessary - according to the standards?

2
PWHT is like anything else, its necessary in engineering when required by regulation or design considerations. Without telling us what industry you're in all we can do is guess that you're looking for the proverbial magic design guide covering all industries and situations, none of which exists. As I tell many junior engineers - dont waste time hoping others will do your job, learn engineering and the regulatory requirements for your industry. The worst excuse when failure occurs is, "bc ISO/ASME/internet said so."

RE: When is PWHT necessary - according to the standards?

(OP)
@ DVWE, I have seen some ASME IX documents but I'm not versed at all in the design parts. But I'll browse through them.

@ DekDee and gtaw, thanks for the specific references. I actually have those, I'll finally have to read them thoroughly.

@ CWB1, why would you need to know what industry I'm in? Does steel in offshore applications react different to welding as the same steel when used in the oil & gas industry? I hope I didn't give the impression I'm a junior engineer. I also mentioned explicitly I don't need input on when to perform PWHT, as I'm well aware of that. I need this again for bureaucratic reasons, as I'm working this time in an industry where paperwork is at least as important as the actual work.

RE: When is PWHT necessary - according to the standards?

kingnero,

DekDee and gtaw have given you some good references. Specifically with ASME, the two I use the most - and I would venture to say are the most commonly used in the USA - are Section VIII, Div. 1 for pressure vessels and B31.3 for pressure piping. Have a look at UCS-56 in Section VIII for PWHT requirements for carbon and low-alloy steels. PWHT requirements are within the Fabrication and Erection section of B31.3.

Both of these codes require PWHT based on the thickness of material. However, in the oil and gas industry and other chemical industries, PWHT requirements are also based on the service the pressure containing vessel or pipe will be used in. What we call "AES" or Aggressive Environmental Service requires uniform hardness of the steel so as to mitigate corrosion phenomena such as stress corrosion cracking. These specific environments are listed in the American Petroleum Institute (API) Recommended Practice (RP) 582. This recommended practice has been heavily adopted in the oil and gas industry, and has become more of a standard. Guidelines on PWHT times and temperatures are a little more conservative than those found in the ASME specifications. It is a great supplemental document to use.

The devil is in the details; she also wears prada.

RE: When is PWHT necessary - according to the standards?

I should have read the inquiry more closely. I was thinking along the lines of preheat. Oops!

Best regards - Al

RE: When is PWHT necessary - according to the standards?

@DVWE

B31.3 has changed a bit from your statement. You might be interested in: https://www.eemua.org/News/New-EEMUA-guidance-on-P...

In terms of exposure environments driving PWHT, there is NACE (AMPP) SP0472, and API RP 945 for example.

Steve Jones
Corrosion Management Consultant

www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

RE: When is PWHT necessary - according to the standards?

Yes. Thanks for that, Steve. That change was nearly 10 years ago and affected only P1 Carbon steels. And, without looking at the code, I believe there are certain preheat and chemistry (like Carbon Equivalency) requirements that must be met for exemption. Low-alloy steels, like P3 thru P91 we’re not affected by the change, so there are still guidelines within the code that apply to those materials.

The devil is in the details; she also wears prada.

RE: When is PWHT necessary - according to the standards?


kingnero (Mechanical),

Your internet country code ( BE) implies Eurocodes are applicable in your zone and i will suggest you to look BS EN 13445-4

( Unfired pressure vessels — Part 4: Fabrication )

The following doc. is useful to get the concept .












Tim was so learned that he could name a
horse in nine languages: so ignorant that he bought a cow to ride on.
(BENJAMIN FRANKLIN )

RE: When is PWHT necessary - according to the standards?

See
1) ASME VIII div 1
a)Lethal service UW-2
b)UCS-79 FORMING PRESSURE PARTS.

2) ASME III Nuclear

Regards

RE: When is PWHT necessary - according to the standards?

In the US,
for structural steel work (not pressure vessel, not aerospace),
for low carbon and HSLA,
for plate thicknesses 1.5 inches (38mm) and less,
PWHT almost never required.

RE: When is PWHT necessary - according to the standards?

Quote:

why would you need to know what industry I'm in? Does steel in offshore applications react different to welding as the same steel when used in the oil & gas industry?

No, but standards are based on industry-specific assumptions and design methodology, full of industry-specific holes, buts, ifs, and contradictions, and generally best not cherrypicked but rather understood as a whole. Reading a variety can be a good intro to a new topic prior to engaging a niche expert and beginning the engineering process, but the intent of standards isn't to teach how nor dictate when or why to do anything so you're simply not going to find what you're looking for. From your comment about needing these for bureaucratic and paperwork reasons, I assume you want to cite standards to support your design decisions. Unfortunately, citing standards to do so should raise a big red flag for most readers.

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