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[MW:8058] RE: 7981] Re: Qualification of PQR & PWHT for Carbon Steel Surfacing on Alloy Steel

By Materials & Welding

Hello Jaspal,

The description of the equipment looks to be that of  "breech lock exchangers or hydrotreater exchangers " used in refineries. I am not sure what your clients' specification is calling for, however API -934E-Recommended Practice for Materials and Fabrication of 1¼Cr-½Mo Steel Pressure Vessels for Service above 825°F (441°C)  and 934C-Recommended Practice for Materials and Fabrication of 1 1/4Cr-1/2Mo Steel Heavy Wall Pressure Vessels for High Temperature, High Pressure Hydrogen Service are well adopted recommended design practices for such services.

Both the RP's call for the following for overlay PQR:-

  • Procedure qualification tests shall be made on base metal of the same ASME specification as specified for the vessel, but either plate or forging may be used.
  • Thickness of the test specimen shall not be less than one half the thickness of the vessel base metal or 2 in. (50 mm.), whichever is less.

  • The welding electrode, wire and flux used for the weld overlay procedure qualification shall be the same type and brand to be used in production.

  • The qualification test plates shall be subjected to the maximum PWHT condition.

Since this is an exchanger, one may have  to stress relieve the tube sheet separately after overlay to meet the PWHT time and temperature cycle. This may arise because in many cases the shells may have lower thickness than tube sheet. If the final PWHT is set according to the shell thickness then the tube sheet may not undergo desired PWHT cycle.
 
Irrespective of the above facts its' advisable to qualify overlay PQR with maximum PWHT (Time and temperature).As per UCL-34, the determining thickness for PWHT shall be the thickness of the base material.
  • UCL-34 specifies minimum  PWHT temperature as 1,200 deg F (650 deg C) and a holding time of 5 hr plus 15 min min minimum for each additional inch(25 mm) over 5 in. (125mm).
  • As per API 934E - PWHT shall comply with the minimum requirements of the applicable code except that all 1¼Cr-½Mo and 1Cr-½Mo weld joints shall be PWHT at a minimum of 1225°F (660°C), and the recommended post weld heat treat range is 1225-1275°F (665-690°C).

  • As per API-934C-PWHT shall comply with the minimum requirements of the applicable code except that all 1 1/4Cr- 1/2Mo weld joints shall be PWHT at 1225°F -1275°F (660°C -690°C).

You may choose one of the above requirements based on clients' requirements.

Note the PQR qualification guidelines for Overlay and Butt welds are not the same.You will require separate qualification and testing guidelines for butt-joints.

Thanks.


Pradip Goswami,P.Eng.
Welding & Metallurgical Specialist & Consultant
Email-pgoswami@sympatico.ca,
pgoswami@quickclic.net

-----Original Message-----
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of JASPAL SINGH
Sent: Monday, November 01, 2010 2:01 AM
To: Materials & Welding
Subject: [MW:7981] Re: Qualification of PQR & PWHT for Carbon Steel Surfacing on Alloy Steel

Dear Sir,

Any reference for the same in the code. Because UCL-34 is for corrosion resistance overlay only.

Regards

Jaspal Singh

On Nov 1, 10:56 am, Prakash Hegde <pb.he...@yahoo.com> wrote:
> Dear jaspal
> It will be considered as weld metal thk and we can consider as weld built  up and accordingly the soaking time can be decided
>
> Regards
>
> Hegde
>
> ________________________________
> From: JASPAL SINGH <jaspaldh...@gmail.com>
> To: Materials & Welding <materials-welding@googlegroups.com>
> Sent: Mon, 1 November, 2010 9:46:25 AM
> Subject: [MW:7978] Qualification of PQR & PWHT for Carbon Steel
> Surfacing on Alloy Steel
>
> Dear All,
>
As per Client Requirement, we need to do the 10mm Carbon Steel Deposit on 250mm Thick Alloy Steel Tube Sheet( 1.25Cr, 0.5Mo).
What will be the PWHT requirement for deposit. If we consider the exemption in UCL-34 (Soaking Time as per deposit thickness), that is applicable for Corrosion Resistance Weld Overlay. Carbon Steel over Alloy Steel is not Corrosion Resistance Overlay.

How to Qualify Procedure for the same or we can use butt welded qualified PQR.

The main issue is PWHT time?

Regards

Jaspal Singh, CWI-AWS, CSWIP-3.1
Quality Assurance
Process Equipment Division
ISGEC, Yamuna Nagar, Haryana -135001
Phone: 911732307251
Ext: 251 Mb: +91 9996624244


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