damage of packing material of SW valve after PWHT at site

[Nivendkar Vinayak (Mumbai - Piping)]

Dear all,

 

In the piping class of alloy steel, we have SW end small bore gate, globe valves. And as per the client requirements all Alloy steel piping joints shall be PWHT after welding.

 

Now , if we performed the PWHT at site at temp. 704-760 Deg C (As per ASME B 31.3 Table 331.1.1 Requirements for heat treatments), then is there any possibility of damage to packing material which is normally graphite due to heat dissipate during PWHT.

 

What type special consideration to be taken in this case. Members are requested to give suggustions.

 

Thanks in advance..

 

Regards,

Vinayak

[Pisat, R. R(ahul)]

hi Vinayak,

 

You are very much right regarding damage to the valve packing .

These SW valve shall be procured with 100 or 150 mm Puff ( a piece of pipe ) welded on both side by.

 

PWHT at valve end shall be done by manufacturer.

 

hope it clarifies.

 

Kind regards

Rahul

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From: Nivendkar Vinayak (Mumbai - Piping) [mailto:V.Niv...@ticb.com]
Sent: vrijdag 20 november 2009 7:34
To: piping...@yahoogroups.com; material...@googlegroups.com
Subject: [MW:3694] damage of packing material of SW valve after PWHT at site

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[Darcy Morin]

If the valves are 'bolted bonnet', consider the disassembly of the valves before PWHT.  If the bonnet is welded to the body of the valve, investigate if a preheat will fulfill your design requirements. 

Alternatively, restrict the rate of heat input during welding by limiting the size of electrode  (SMAW) and the amperage setting. Also limit the interpass temperature and weld bead width.    

Regards,

Darcy Morin

[Rana, Jignesh]

Dear Vinayak,

 

The normal practice is to remove all packing material from valve, before pre heating, welding and PWHT operations. Once NDT of valves completed the same will be re fitted to the valves. The valve manufacturers additionally supply the packing material with valves. In case of critical lines, even the valve manufacturers are called for re packing, assembly operations. The leak tightness will be checked along with the line hydro.

 

 

Regards,

 

JIGNESH R RANA

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From: Nivendkar Vinayak (Mumbai - Piping) [mailto:V.Niv...@ticb.com]
Sent: 20 November 2009 12:04
To: piping...@yahoogroups.com; material...@googlegroups.com
Subject: [MW:3694] damage of packing material of SW valve after PWHT at site

 

Dear all,

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[mohan q8]

HiVinayak,

Rahul is right, but i think you already purchased all the valves without puff pieces. so you can minimize the heat input at gland packing areas by wound the heating coil around the joint only and avoid over valve body and keep open the gland packing (bonet area) for air circualtion/contact which will desipate the heat. During pwht time keep open the gate to avoid damage to valve seat.

Also you can carriout some trial hydrotest for valves with gate 1/2 open condition to verify the gland packing condition. In my perious project i had done some random test and there was no leakage observed that time.

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With Regards,

Mohan, Q8.