RE: PWHT for wled joints in Amine services

From: <Al>
Date: Tue Feb 17 2004 - 13:37:00 EST

kl_m_a
Fair question but heres the scoop.

I think youre missing the point of PWHT. its not like radiography where testing some is a measure of all, applying PWHT to some is not a measure of applying it to all weld joints. the point is the refine the grain and improve the resistance to cracking. there are three components to SCC (experienced in amine),

1. has to be the environment present.. yes
2. has to be tensile stress present... yes
3. has to be a source of crack initiation.. crevice corrosion and a number

of other mechanisms are readily available. (eg defect)

Why would some be immune (needing PWHT) and not others. I guess you could say concentration (LA/RA) . Read on.

Further... Cracks can be parallel or normal to the welds depending on the orientation of the principal stresses. Cracking can be trans or intergranular.Widespread opportunity/latitude for failure in the microsructure. Used to be that PWHT only used to be done when the amine service was above 150F and acid gas content >75% CO2 or >200F for any concentration. From widespread experience in many many plants and refineries of all sorts of cracking in all situations ,,it is now mandated on all welds in amine service. Cracking has been widespread in all situations w/o PWHT, but very very rarely reported in drums tanks or piping WITH PWHT. I cant think of a single instance but there might have been somewhere.. If failure it has always been other causes. Point is , dont try to shortcut this. Experience says you will DEFINITELY have problems, probably widespread.

-----Original Message-----
From: k1_m_a [mailto:k1_m_a@yahoo.com]
Sent: Tuesday, February 17, 2004 6:03 AM To: PipingDesign@yahoogroups.com
Subject: [PipingDesign] PWHT for wled joints in Amine services

Hi,

Can anybody help me making a good decision regarding the necessity of PWHT for weld jionts in Amine services?

We are in construction part of a Gas Sweetening EPC project containing three type of Amine services. A (Amine), AL ( Lean Amine) and AR (Rich Amine).
Based on the criteria defined by the Amine plant designer engineer, we have done PWHT only for weld jionts in AR ( Amine Rich) lines. But now, we are under pressure by the Client that in any Amine service including A, AL and AR all the weld jionts shall be Post Weld Heat Treated.

Your kind answer based on your engineering practices, helping me to convince the Client that PWHT is not needed for A and AL services (or can be done only for some limited number of welds) is most appreciated.

I will be glad to give any more necessary information if needed, e.g. Gas composition, etc.

Thanking you,

Keivan Mashayekh

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Yahoo! Groups Links Received on Tue Feb 17 13:37:00 2004