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Interrupted pipe welding

Interrupted pipe welding

Postby Pieltro » Thu Oct 24, 2013 11:34 am

We were doing a 32" pipe weld, WT=27mm A106 Gr.B, but lunch time came and the welders left leaving only the root pass complete, I know this is not a good practice but I don't understand very well why.
Could you clarify why the interruption of welding is not a good practice. Thanks.
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Re: Interrupted pipe welding

Postby mawsamit » Thu Oct 24, 2013 2:22 pm

The interruption of the welding is not a problem if you follow the WPS from the point that you have left it. When a welding is interrupted, we shall do the "post weld heating" (if applicable) and leave the joint until we are to continue the welding where we shall do the "preheating" (if applicable) and then perform the welding following the WPS from the point that we have left it. In case that the WPS doesn't specify neither "post weld heating" nor "preheating" we shall simply continue the welding without taking extra measures.
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Re: Interrupted pipe welding

Postby mohd » Fri Oct 25, 2013 5:15 am

dear one,

Welding should not be interrupted or leave before root and hot-pass.

In addition, when you have to use external or internal clamp for fit-up, if you not stringing properly, there is the chance that the pipe's fit-up may be disturbed. Moreover, if your code is the API 1104 and if a clamb is used, the minimum percentage of root-bead welding that must be completed before the clamb is released shall be specified as indicated by the API 1104.

You can educate your welder and set your welding start-up time accordingly.

regards,
mohd.
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Re: Interrupted pipe welding

Postby Ballbearing » Fri Oct 25, 2013 12:11 pm

Pieltro,
The main concern is the possibility of cracking due to the contraction of the weld during cooling.
The thick pipe creates a "heat sink" and this can cause accelerated cooling and shrinkage which may be a problem if you do not have sufficient weld metal in place.
If the pipe is not under external pressures and the correct preheat has been used then you should have no problem but it is recommended to wrap the weld joint with a heat blanket to slow the cooling.
Hope that helps,
Cheers,
BB
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Re: Interrupted pipe welding

Postby wefel » Fri Oct 25, 2013 5:20 pm

Mohd,

Please let me partially disagree with you since hot pass is used:
1. to melt and float out the worm tracking (known also as wagon tracks) which have been left after the completion of the root pass (please let me explain for those that are not aware of worm tracking that it is a weld defect that is caused due to solidification process of weld puddle that starts before the hydrogen can completely escape and so the trapped hydrogen flows as a bubble from the weld puddle into the atmosphere and results in such a weld defect),
2. to perform "heat treatment" (self heat treatment, as each consequent pass does to its preceding pass during welding) to the root pass and thus to eliminate microstructure that is prone to "hydrogen induced cracking" as well as to reduce the hydrogen content by allowing the hydrogen to release from the weldment into the atmosphere as the "hydrogen bake out" does.

So, we shall use hot pass whenever the root pass has been performed with a "non low hydrogen" filler metal (eg: E6010 SMAW electrode). Instead, if the root pass has been performed with GTAW process (eg: ER70S-6 filler metal) then there is no need for performance of hot pass.

Regarding your comment for fitting up with clabs for welding under the scope of API 1104, I would like to highlight that "the minimum percentage of root-bead welding" specified in API 1104, par. 5.3.2.11 has nothing to do with the hot pass since such an extra pass(es) simply intends to strengthen the root-bead in order to prevent its possible break down due to the existing stresses after the clamb is released. The relevant to hot pass paragraph in API 1104 is the par. 5.3.2.10 (time between passes) that specifies: "the maximum time between the completion of the root bead and the start of the second bead, as well as the maximum time between the completion of the second bead and the start of other beads, shall be designated”.
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Re: Interrupted pipe welding

Postby Pieltro » Thu Apr 10, 2014 3:36 am

Thank you everyone for your answers, it is always good to hear experiences from others.
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Re: Interrupted pipe welding

Postby Logosweld » Wed Apr 30, 2014 3:31 pm

Ballbearing wrote:Pieltro,
The main concern is the possibility of cracking due to the contraction of the weld during cooling.
The thick pipe creates a "heat sink" and this can cause accelerated cooling and shrinkage which may be a problem if you do not have sufficient weld metal in place.
If the pipe is not under external pressures and the correct preheat has been used then you should have no problem but it is recommended to wrap the weld joint with a heat blanket to slow the cooling.
Hope that helps,
Cheers,
BB

very true totally agreed
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Re: Interrupted pipe welding

Postby Logosweld » Fri May 09, 2014 3:36 pm

i think all have shared their own views and its quite wonderful to know the views of others,its a kind of new experience
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Re: Interrupted pipe welding

Postby Logosweld » Thu May 15, 2014 4:36 pm

wefel wrote:Mohd,

Please let me partially disagree with you since hot pass is used:
1. to melt and float out the worm tracking (known also as wagon tracks) which have been left after the completion of the root pass (please let me explain for those that are not aware of worm tracking that it is a weld defect that is caused due to solidification process of weld puddle that starts before the hydrogen can completely escape and so the trapped hydrogen flows as a bubble from the weld puddle into the atmosphere and results in such a weld defect),
2. to perform "heat treatment" (self heat treatment, as each consequent pass does to its preceding pass during welding) to the root pass and thus to eliminate microstructure that is prone to "hydrogen induced cracking" as well as to reduce the hydrogen content by allowing the hydrogen to release from the weldment into the atmosphere as the "hydrogen bake out" does.

So, we shall use hot pass whenever the root pass has been performed with a "non low hydrogen" filler metal (eg: E6010 SMAW electrode). Instead, if the root pass has been performed with GTAW process (eg: ER70S-6 filler metal) then there is no need for performance of hot pass.

Regarding your comment for fitting up with clabs for welding under the scope of API 1104, I would like to highlight that "the minimum percentage of root-bead welding" specified in API 1104, par. 5.3.2.11 has nothing to do with the hot pass since such an extra pass(es) simply intends to strengthen the root-bead in order to prevent its possible break down due to the existing stresses after the clamb is released. The relevant to hot pass paragraph in API 1104 is the par. 5.3.2.10 (time between passes) that specifies: "the maximum time between the completion of the root bead and the start of the second bead, as well as the maximum time between the completion of the second bead and the start of other beads, shall be designated”.

good answer and nice said about the interrupted pipe welding
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Re: Interrupted pipe welding

Postby Logosweld » Fri May 23, 2014 3:38 pm

nice experience to be gained from others really nice posts sound good
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Re: Interrupted pipe welding

Postby Logosweld » Thu May 29, 2014 3:16 pm

all have posted nice post regarding the interrupted pipe welding...all have new ideas and their own opinion regarding this so good one
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Re: Interrupted pipe welding

Postby Logosweld » Mon Jun 02, 2014 5:43 pm

interrupted pipe welding is done in some cases but using it as normal would not be so effective because it will degrade the welding efficiency of the metal to be welded because it will be the welding having interruption.
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Re: Interrupted pipe welding

Postby DonaldE » Mon Aug 03, 2015 10:25 am

i think it is always good to have experienced people around here and it is very knowledgeable for newbies to learn a lot from that
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