welding activity pipeline 8

[ceasar20]

Hello ;
We work for welding activity pipeline 12” X52 thickness 8.38 mm

Root / hot pass GTAW

Filling / cap SMAW

In order to optimize production Contractor propose to proceed with GTAW first , for example for he weld first 10 weld joint GTAW after that he come back tomorrow with and filling and cap weld joint with SMAW.

It’s some issue for that ?

 

[LittleInch]

Dor 20.

This is usually covered in the welding procedure.

Interpass temperature is key as is the maximum time between passes. Only if this procedure was part of the welding procedure test will it be valid.

It might be ok but I think it will need pre heat before the filing.

Try asking this question in the welding forum

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Everybody has questions, comments and opinions. What's needed is answers.

Reality used to affect the way we thought. Now we somehow believe that what we think affects reality.

 

[austsa]

GTAW is not suited for field welding as you will need to have very good shielding from even slight wind.

 

[SJones]

It's also not a good practice to deliberately leave numerous partially completed welds.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[weldstan]

GTAW is often used in the field for root and hot pass welds of pipe and yes sheltering from wind is required. Generally the fill and pass crew will follow shortly after completion of the root and hot pass and it is assumed that SMAW will be performed with low hydrogen electrodes. In welds so thin in X52 pipe, no preheat is anticipated unless the ambient temp is near or below freezing. We have made hundreds of thousands of welds in low carbon steel pipe in this manner.

It is a different story when welding the root and hot pass with cellulosic electrodes where I have seen numerous cracking incidents after depositing the root and hot pass and waiting some time including as much as a day between filling and capping.

 

[Dhurjati Sen]

I agree with weldstan Sir, ABSOLUTELY. Seconding a post could have a favourable impact on the OP, at least that's the premise.

DHURJATI SEN

 

[ceasar20]

Thank you

 

[HTURKAK]

weldstan : Excellent respond... wish I could give you two stars.

By noting this, I'm informing others to look this respond.

 

[r13]

weldstan,

Just to make sure I understand correctly - it is not a matter of time in between the two welding process, but the electrode used for the root and hot pass. Please correct me if I'm wrong. Thanks.

 

[1503-44]

It is a matter of temperature control and the temperature of the primary weld having dropped too low before making the secondary weld, maybe without preheating, which is normally not necessary for 8mm, and will also tend to reheat the primary. Wind tends to cool the pipe and weld differently and can also introduce water droplets, especially offshore, sand and other impurities.

Reality used to affect the way we thought. Now we somehow believe that what we think affects reality.

 

[LittleInch]

It would be nice to see or know what the particular welding procedure says....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[weldstan]

r13, It is not a function of time between root/hot pass with the GTAW process (low hydrogen) and fill and cap with low hydrogen SMAW electrodes in thin low carbon steel pipe. For one reason, the root and hot pass with vertical up progression will normally fill 4 to 5mm of the weld. One must, of course, avoid high applied stresses to the pipe when the weld is incomplete. From an overall cost standpoint, it is best to complete the weld in the shortest time frame. I have seen the root and pass crew wait hours doing nothing for the fill and cap crew to appear when they could have completed the weld with no more than 2 additional passes within the confines of the WPS.

With typical pipeline welding using cellulosic electrodes, the root and hot pass is done in the vertical down progression and the thickness of the deposit is generally less. And because it is not a low hydrogen process, delayed hydrogen induced cracking is a real possibility, especially when the ambient temperature is low. So it is best that the fill and cap team closely follow with their fill and cap welding.

 

[r13]

weldstan and Fourteen,

Thank you both, especially weldstan for the clear explanation.