PWHT Requirements in Pressure Vessel Inspections

by Murali
(UAE)

What are PWHT requirements in pressure vessel inspections?

Bob's Reply: I prefer to answer to this question in two separate questions as below:

1. When and where PWHT is mandatory by code requirement?

2. How PWHT must be done when it is mandatory?

Pressure Vessel Inspections-Answer to question 1:

If we focus only in ASME Code Section 8 Div 1, there are lots of conditions which cause the PWHT to be mandatory. Some of them are:

a) Based the requirement of UW-2(a) when our service is lethal and our material is carbon steel or low alloy steel.

b) Based the requirement of UW-2(c) when our pressure vessel is unfired steam boiler and our material is carbon steel or low alloy steel.

c) Based the requirement of UW-2(d) when our pressure vessel is subjected to direct firing and our material is carbon steel or low alloy steel.

d) Based the requirement of UCS-56 when our nominal thickness exceeds a specific value, for instance 38 mm for P No.1 material or 0 mm for P No.3 material.

UCS-56 also gives min. PWHT temperature and min. holding time (soaking period) based on P-Nos. and thickness respectively.

e) Similarly to the UCS-56, the same apply for other martial groups i.e. UNF-56, UHA-32, UHT-56 and etc.

f) Based the requirement of UCS-68(b) when our MDMT (Minimum Design Metal Temperature) is below -55 Degree F.

Pressure Vessel Inspections-Answer to question 2:

When one of above requirement applies to us, then we must do PHWT based the requirement of UW-40 which detail to us the PHWT procedure.

Some important requirements in this clause are:

a) For Furnace PWHT, Loading Temperature shall not exceed 800°F, heating rate 400 deg F/hr/inch of thickness, cooling rate 500°F /hr/inch of thickness.

Still air cooling permitted below 800°F. During soaking period, temp difference between hottest and coldest part shall not exceed 150°F.

b) Minimum overlap for PWHT in multiple heats is 5 ft.

Comments for PWHT Requirements in Pressure Vessel Inspections

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Sep 05, 2022
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Alternative PWHT NEW
by: Anonymous

Kindly let explain about alternative PWHT as per ASME SEC VIII DIV 1 and ASME B31.3?

Jan 02, 2021
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PWHT for Eliptical Head
by: Prashant

Dear Sir

Is PWHT required for welded seam in Eliptical Head of 10 mm thick as per which clause of ASME.

Thank You

Oct 09, 2020
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UCS-68(b) PWHT exemption of P No 1
by: Hemant Solanki

1. it is the intention of code to post weld heat treat category C and D welds, even though Category A and B are exempted from PWHT as per UCS-68(b)(1)?

2. I have doubt how for Cat.A & B Type 1 i.e. double welded butt joint (which will deposit more welding and welding stresses) is exempted from PWHT but why Type 3 i.e.single welded butt joint not exempted from PWHT ?

Is PWHT required for other attachments welds, where stress in the weld exceeds 25% of the allowable stress of the material?

Jul 14, 2020
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PWHT for cyclic service equipment
by: Anonymous

Heater vessel is made of LTCS material (SA-516 Gr60N)+ Sour service+ Cyclic service.
Is it mandatory PWHT is required as per ASME sec. VIII Div-1?

Jan 31, 2020
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PWHT TECHNICIAN
by: Jitendra Kushwaha

mr Jitendra Kushwaha PWHT TECHNICIAN Indane experience 3 years pipeline workshop palant . Email.(kushwahajitendra48325@gmail.com) Mobile no 8299156030

Jul 20, 2019
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PWHT for base frame
by: Sumit

I am working in oil & gas industry ,
we also manufacture base frame .
we manufacture base frame of size below in i beam.

pprox Dimensions - 11000 mm x 5000 mm x 3000 mm

Beam thickness - 20 thk

SR cycle - As per UCS 56

Approx wt. - 30 tons

and also used one plate of thk 150 mm.

So which thickness (20 mm or 150 mm) consider to choose soaking time.

Sep 03, 2018
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PWHT for bigger of pressure vessel dimension NEW
by: Hari

I would like to asking

we have proposed order for PWHT large vertical Vessel fabrication with height 15000mm and diameter 14200.

if we see the vessel dimension is bigger can we proposed by local PHWT for joint only since we consider to looking the big furnace and transportation problem.

can we propose by local heating (PWHT) by joint only?

Apr 03, 2018
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pwht NEW
by: Anonymous

i am working in a pressure vessel head manufacturing company. i want to know about pwht. are pwht is done in entire head or just in a test plate weld only ? we are doing three types of heat treatment such as normalizing, solution annealing, stres relieving which is done based on fiber elongation value.

some of the heads blank has no weld seam and some heads has weld seam in blank..

my question is pwht is done in entire welded heads or in a weld test plate ?

Apr 05, 2017
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ASME SEC 8 DIV 1? WATER TREATMENT NEW
by: Anonymous

IF WE FOLLOWED PRESSURE VESSEL MANUFACTURING AS PER ASME SEC 8 DIV 1 THEN WE MUST FOLLOWED PWHT ?
IF VESSEL USED FOR WATER TREATMENT APPLICATION AND WORKING PRESSURE IS BELOW 1.1-1.2MPA???

Jan 14, 2017
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Ddai Ramakrishna NEW
by: Anonymous

PWHT vessel inspection HARDNESS readings to be taken before and after Post weld heat treatment ..then only we know the difference before and after PWHT VALUES.

Apr 25, 2016
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ss NEW
by: Anonymous

you will change the microstructure

Aug 28, 2015
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PWHT due to UCS-79(d) NEW
by: Anonymous

Is PWHT mandatory following the welding of a head to a vessel when the extreme fiber elongation of the head is more than 5% and the thickness is more than 5/8 in.?

Feb 03, 2014
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PWHT for Lethal Service NEW
by: Essam Hassan

In case, PWHT is mandatory because of the lethal service.
What is the min holding time?
is it based on the thickness and then get the value from table UCS-56?
or it is 15 minutes for all cases?

esshassan@yahoo.com

Jan 08, 2014
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PWHT NEW
by: Rafik

Hello,

It's true that For the vessels that will undergo PWHT, The nozzle connection shall be as per Fig. UW-16.1 (f-1),f-2), f-3) & (f-4)

Thank you.

Regards

Oct 22, 2013
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CTOD in-lieu to PWHT NEW
by: Anonymous

Can PWHT replace by fracture toughness test i.e CTOD?

Oct 05, 2013
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pwht NEW
by: Anonymous

very good

Apr 27, 2013
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hardness test after PWHT NEW
by: vubadien

Dear Sirs,
could anyone help you to explain below concern???

I've a concern about hardness test requirement after PWHT.
I am now inspect the vessel fabrication by ASME VIII div.2 with material SA-516 Gr70 thickness 60mm so after PWHT it is whether hardness test after PWHT or not and is it a scope of A.I?

Jan 31, 2013
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PWHT temperature exceedance NEW
by: Welder1

Is there accepted by the ASME Code to use a higher PWHT temperature on the product compare with what you have qualified your QPR according to - example you WPQ is qualified with 580 deg.C, and the product is PWHT with 620 deg.C.
Is that accepted according to ASME Code?

Sep 26, 2012
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PWHT holding time effect NEW
by: Anonymous

IF PWHT holding time increases the Tensile value will reduce,

To confirm the tensile applicability at the extended holding time, the check test performed,
Example The vessels which need in service PWHT apart from fabrication PWHT, check test (Simulation test) will conduct for mechanical properties with a Fabrication PWHT holding time plus service PWHT holding time

Aug 26, 2012
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QUERIES IN PWHT NEW
by: SRINIVASAN

WHAT ARE THE EFFECTS WILL HAPPEN IF EXCEED THE SOAKING TIME AGAINST THE REQUIRMENTS WHILE DURING THE PWHT?

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