Interpass timing

[jesti fer]

Dear experts,

I need your help, In our project (B.31.3) CS pipe joints ASTM A106 Gr.B 8” Sch XXS, our construction team kept the joints after root pass and hot pass welding, but our QC instructed to cut and and re-weld the joints. Really it is required and  it is mentioned any were in code? We are maintaining preheat at 150-Deg and inter pass temp 300-Deg

Please help me;;;;

[murugesan jeyaraman]

Hi

 

The main reason for imposing restiction such as "1/4 of thickness shall be completed at the end of a day work, or jonts shall not be left overnight after welding root and hotpass" is not to stress the welds due its own weight of pipe line or some other restrains which may stress the component and may develop crack. (This statement is true only for carbon steel welding atleast).

 

so, in your case, you can do MPI testing of hot pass weld then pre heat to 300 degree celsius (to maintain interpass as well as preheat temperature), then proceed to complete the welding.

 

Murugesan

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[DEBASISH]

Dear

Interpass means temperature (3" on either side of joint) inbtween two consecutive passes. And in this case if it is left after laying Root & Hotpass all through out the shit/night, then you tell me where is the essence of the word interpass.-Unless otherwise it has ben kept under the preheat you mentioned all through out the break.

 

As far as my knowledge goes, there is no code reference about this GEP(Good engineering practice). Basically this is a truely a welding-metallurgical aspect and if the joints are so critical, then your QC has right to say so.

Actually what happens: With only two passes laid on this XXS heavy wall thickness parent metal, the weld deposit thickness is not that much to withstand the contractional forces exerted by the parent metal from both side of the joint. Thereby resulting huge stress build up which leads to cracks. In heavy walled plates as well as pipes, longitudinal ( cold cracks / HIC ) on the bead laid yesterday are often seen in this partially welded items.

 

Way forward: May be at the best if you can put a deviation note and convince yourself as well the QC that it will be 100% NDT done before proceeding further. 100% LPI & 100% MPI on all such partially welded joints. And marking these joints with a distint identification no. and doing 100% RT of all these particular joints after final weld completion., even if the drg says % RT on all finished joints.

 

regards,

Debasish

Dubai. 

+971504349936 

 

 

[salman cader]

yo Debasish

As far as interpass temp is concerned ....if you speaking of a 75mm
plate ...or more than 50mm.Interpass temp shall be measured on the
weld metal or immidiately adjacent to that heat being focused....allow
2minutes for every 25mm..then you good to go........
Go to your WPS and you will see interpass temp which is given in KJ

ON another note preheat ranges from 50 -250 degrees celcius

Interpass temp is measured in KJ so work out your HI and AE

[DEBASISH]

Dear sir,

[pradeep kumar mishra]

Dear
This is only Good engineering Practice. You can perform MPI if there is any reason to doubt
for crack development. Otherwise it should not be cut.
Anyway final NDT is going to be performed.
There no such code requirement and I strongly recommend not to cut the same.

P.K.Mishra
Ahmedabad, India

On Fri, 17 Feb 2012 10:46:13 +0530 wrote

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