Re: [MW:4800] PWHT of Hydrotesting vents in Sour gas service

 

Hi,

 

Material of nconstruction is Carbon steel suitable for sour gas service with P & S restriction. Code- B31.3.

 

In original plan, all Sour gas pressure pipeline Hydrotest vents were of flanged connection with Blind flange.

 

in the exisiting plant, we encountered lot of leakages in this flanged joint which leads to emergency shutdowns.

 

So we want to avoid flanged joints for closing Hydrotest vents. The no. of hydrotest vents are more, there is a serious concern

 

Our specification says threaded joints are not acceptable for Sour gas service, as there is possiblity of leakge due to corrosion.

 

To balance all the criterias, we planned to provide threadolet on the pipelines as hydrotest vent.

 

After PWHT & hydrotest all the vent ends will be closed with Plugs( threaded joint).

 

 To avoid any leakage we want to provide a seal weld (fillet joint). as the rating of joints are 600# & above.

 

This fillet joint is critical as we don't want to end up again in same trouble in a different way.

 

 

Please advise on avoiding PWHT for this joint & suitable electrode for this CS joint.

 

Thanks 

 

Suresh 

 

 

 

 

 

 

 

 

 

 

On Mon, Apr 12, 2010 at 2:40 PM, Kathalingam Babu <kathalingam.qaqc@ppl.com.sg> wrote:

Hi

 

May i know, which spec. says , sour gas service needs mandatory PWHT ?

 

Regards,

 

K.Babu

 

----- Original Message -----

From: Prabhu Kumar L

To: materials-welding@googlegroups.com

Sent: Monday, April 12, 2010 12:30 PM

Subject: RE: [MW:4793] PWHT of Hydrotesting vents in Sour gas service

Dear Suresh,

 

Please note that the intension of PWHT is to relieve the stresses from HAZ and weld metal as well. Use of Inconel or any other electrodes will not relieve the stresses from HAZ, and it remains same for all electrodes. Hence you cannot avoid PWHT. In order to reduce difficulties in PWHT you can propose the method as follows.

 

• Buttering (weld overlay) of 5mm (if it is CS you can use same electrode) on the locations where weldolets to be welded to main pipeline.
• After buttering, local PWHT shall be carried out as per procedure.
• Welding between weldolet to buttered layer shall be done without PWHT.

 

The HAZ is a critical area which need to stress relieved. Also note that in general, the weld metal is softer than HAZ since, it contains very low % carbon and other minor alloying elements to improve slight toughness also.

 

Regards,

 

L. Prabhu kumar,

Sr. Principal Engineer,

 

Equipments & Materials Dept.,

Saipem India Projects Limited,

Nungambakkam High Road, Chennai - 600 034, India.

Tel:+91 44 43906588, Ext.: 588, Fax:+91 44 66840345,

Mobile Ph. No.: +91 9003010978.

---

From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of suresh venkat
Sent: Sunday, April 11, 2010 4:49 PM
To: materials-welding@googlegroups.com
Subject: Re: [MW:4786] PWHT of Hydrotesting vents in Sour gas service

 

My intention was to weld with Inconel Electrode  so as to have soft weld metal.

 

Further opinions will be more helpful.

On Sun, Apr 11, 2010 at 4:10 PM, Raghuram Bathula <raghurambathula@gmail.com> wrote:

what if you weld with SS (ER/E309) or Inconel? members pl share ur opinion

 

On Sat, Apr 10, 2010 at 10:46 PM, suresh <atozsuresh@gmail.com> wrote:

we have sour gas pipelines with higher & lower pressure. All the
pipelines are with Hydrotest vents which will be closed after
Hydrotest.

For low pressure pipelines we use flanged joint with a Blind flange.
For high pressure pipe line with flanged connection there is
intermittent leakages which needs immediate attention even sometimes a
shut down.

We  intend to use a threadolet as vent & will be plugged & seal welded
after hydrotest. The problem is with PWHT. As all the lines in Sour
gas services shall be PWHT.

We want to avoid PWHT of this small fillet joint, Due to the location
of these joints & difficulty in PWHT. but it is dangerous to leave it
without PWHT as it may crack due to residual stresses.

Can you suggest any welding procedure & electrode to have this welding
with reduce hardness HRC 22 Max  by which PWHT can be avoided.

Thanks

Suresh

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