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Up Topic Welding Industry / General Welding Discussion / Post Weld HEat Treatment
- - By Satish Date 04-10-2016 07:34
2 pipes with same OD, one with thickness 19.05mm and the other with 26mm. Welding these 2 pipes require chamfering of 26mm thickness pipe to match with that of 19.05mm. Is it required to perform PWHT for this ?
Parent - - By kcd616 (***) Date 04-10-2016 07:48
14" pipe sch 80 and 120(correct me here, if I am wrong)
PWHT is the EOR's call
and depends on the material
ferrous or non-ferrous is a good start
need way more info
to really help and make a decision
Parent - By js55 (*****) Date 04-11-2016 12:05
Keep in mind there is no EOR in ASME. And we don't know the code of construction yet.
Parent - - By weldnote (*) Date 04-11-2016 14:37 Edited 04-11-2016 14:43
Unless the code or client requires it, it is not mandatory, and either the codes or the clients' contracts are usually very clear about the limits above which you are required to do.

Anyway, the PWHT requirement is usually to the weld itself. And if you are going to reduce the thickness of one of the pipes to 19.05, the weld itself is 19.05 mm and as such you should use this value for determining PWHT, unless there is a specific clause in your clients' contract that refers to this situation specifically

Regardless, be aware that PWHT and Preheating is done primarily to reduce the possibility of fissures due to cold-cracking on the steels and as such you should not stop doing it if you feel there is a possibility of this occurring (making it even more expensive than not doing the PWHT). For example if the 26mm section is completely adjacent to the weld zone, you should consider performing this PWHT, as the 3D heat flow through the steel might be quick enough to cause problems
Parent - - By ssbn727 (*****) Date 04-17-2016 09:01
Here's something to chew on...:grin::lol::yell::wink::cool:

Post Weld Heat Treatment (in accordance with AWS D10.10M)

Post Weld Heat Treatment is performed after welding, generally at a higher temperature and with different objectives than Preheat/Interpass heating. PWHT may need to be applied without allowing the temperature to drop below the specified minimum for Preheat/Interpass heating. So in short you may have to apply the PWHT method with the work piece at temperatures up to 600° F (316° C).

Local PWHT of carbon and low alloy steels is typically performed below the lower critical transformation temperature and is therefore referred to as subcritical. The lower and upper critical transformation temperatures indicate where the crystal structure of steel begins and finally completes a change from body centered cubic to face centered cubic upon heating (the reverse upon cooling). And what this is saying, the molecules of the alloy will rearrange them self to a different configuration if we allow the temperature to reach the upper critical transformation. That will cause the properties of the metal to change, such as hardness and ductility.

There are several reasons why local supercritical PWHT (above the upper critical transformation temperature) such as annealing or normalizing is not desirable. First and foremost, the temperature gradients inherent to local PWHT would produce subcritical, intercritical and supercritical temperature regions. Depending upon the prior heat treatment of the material, this could result in a detrimental effect upon properties (tensile/yield strength and impact toughness) and/or local inhomogeneity (irregularity). Additionally, reduced material strength at supercritical temperatures creates a greater likelihood for distortion.

Post Weld Heat Treatment can have both beneficial and detrimental effects. Three primary benefits of PWHT are recognized. These are tempering, relaxation of residual stresses and hydrogen removal. Consequential benefits such as avoidance of hydrogen induced cracking, dimensional stability, and improved ductility toughness and corrosion resistance result from the primary benefits. It is important that PWHT conditions be determined based upon the desired objectives. With regard to local PWHT this is especially true for stress relaxation.

For reasons relating to carbide precipitation and the need for rapid cooling, localized solution annealing of austenitic alloys such as 300 series stainless steels is also generally not desirable. The discussion of PWHT below and in other parts of the document refers to subcritical PWHT, unless otherwise noted.

There's more here:

Enjoy the read!:eek::grin::lol::roll::smile::wink::cool:

Parent - By MBSims (****) Date 04-23-2016 04:21
Some critical information is missing in order to answer the question. What code or standard must the weld comply with? What is the material specification and grade for the pipe?
Up Topic Welding Industry / General Welding Discussion / Post Weld HEat Treatment

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