PWHT OF VESSEL ?

niraj_kuwait · **Posted:** Mon Jul 23, 2007 11:25 am

WHAT ARE THE GOVERNING PARAMETER FOR DECIDING PWHT OF VESSEL-AS PER CODE.?

1- SERVICE REQUIREMENT

2- % FIBER OF ELONGAITON IN DISH

3- THK OF ANY PRE. PARTS-ABOVE OR EQUAL TO 38MM

PL. TELL ME IS THERE ANY OTHER WHICH I HAVE MISSED?

Frohnert · **Posted:** Mon Jul 23, 2007 3:44 pm

Hello Niraj,

I think bullet point 2 doesn´t belong to "welding" but to cold forming (UCS-79). You can perform a heat treatment for these items before welding, in this case you do not need to push the whole vessel into the furnace, isn´t it?

Maybe it´s better to change bullet point 3 simply to "material".

Michael

akonrad · **Posted:** Mon Jul 23, 2007 4:32 pm

Niraj,
There happens to be quite nice place in SecVIII-1 which might be of great interest to you. See UCS-56: Requirements for Postweld Heat Treatment. Take your time, read it thoroughly- you don't seem to know it.

Juergen Fleischfresser · **Posted:** Mon Jul 23, 2007 9:39 pm

Hello Niraj,

Bullet point 1:
PWHT is required because of service conditions
-acc. to UW-2(a) for lethal service if carbon or low alloy steels are used
-acc. to UW-2(d)(2) for parts subject to direct firing if low alloy steels are used and for c-steels greater than 16 mm
-acc. to. UCS-68(b) for low temperature service below -48°C

Bullet point 2:
see statement of Michael

Bullet point 3:
For PWHT see UW-40. This paragraph is the master-paragraph for PWHT. You find the referenced paragraphs to all applicable paragraphs for PWHT in subsection C: UCS-56, UHA-32, UNF-56, UHT-56. You will see in this paragraphs that the thickness is only one variable for PWHT requirement.

An additional reason for PWHT is UCS-68(c) in order to get 17°C credit to avoid impact testing of P-No. 1 material.

Hope that helps

niraj_kuwait · **Posted:** Tue Jul 24, 2007 6:58 am

Nice Descriptive Information -Juergen Fleischfresser thanks for that

Thanks Michael & Akonrad.

tong2je · **Joined:** Tue Sep 29, 2009 8:09 pm **Posts:** 9

Dear All

What is a permissible/allowable number of PWHT to be carried out on a vessel? For example 1 vessel has been PWHT, NDT after PWHT revealed defect, repaired and then re-PWHT. After second PWHT, NDT carried out and revealed defect again..In this situation what is permisssible/allowable number to re-PWHT. It is any effect on material?

niraj_kuwait · **Posted:** Mon Nov 02, 2009 1:37 pm

Code is silent about No. of PWHT : Technically, the base material properties shall be predictable anticipating the heating/colling cycles,
That is the reason some clients want simulated heat treated condition test results with 2 or 3 cycles of PWHT imposed and mechanical testing carried out on test coupon.

Gonzaga · **Joined:** Sat Dec 15, 2001 1:00 am **Posts:** 657

niraj_kuwait wrote:

Code is silent about No. of PWHT : Technically, the base material properties shall be predictable anticipating the heating/colling cycles,
That is the reason some clients want simulated heat treated condition test results with 2 or 3 cycles of PWHT imposed and mechanical testing carried out on test coupon.

When impact testing is required, this is a must, see Sect.IX (supplementary variables)
mauro

PWHT OF VESSEL ?

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