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Up Topic Welding Industry / Welding Fundamentals / Prohibited Weave on A106 Pipe; also, Better End Prep?
- - By tom cooper (**) Date 05-28-2008 15:06
Attached are views of a 3" sched 160 (ASTM A106 Grade A) pipe joint to be tacked in place, then removed for finished welding. Bevels are 37.5 degrees, with about a 1/8" flat (or land). The chill ring is a Robvon product. Our intention is to tack and root with GTAW (70S-6) and fill out with SMAW 7018.    This joint is a repair on some hydraulic machinery and the joint configuration is driven by the customer who required the ring (or alternatively would allow backing gas, for which we do not have a procedure or experience).

We are also prohibited from weaving according to the Military spec under which this requirement must meet.

Two questions please are this:

1.  Why do you think weaving is prohibited since the material is only mild steel?  I understand the possible heat issues with weaving, but is this really a concern with plain carbon steel pipe?
2.  We think the gap is too wide (about 3/16") and think it will cause trouble if we are not allowed to weave,  or it should be wider so that a second stringer can be more easily melt in and that the edge prep should have been more of a knife edge.

Any thoughts/advice from more experienced pipe welders? Thanks.

Attachment: PipewChillRing1.JPG (18k)
Attachment: PipewChillRing2.JPG (493k)
Parent - By pipewelder_1999 (****) Date 05-28-2008 15:13 Edited 05-28-2008 15:17
Weaving may not be the issue as much as the companies concern for heat input.

More heat=Larger Grains=Less toughness. In many situations this would not be a concern however in systems subjected to cylic loading and sudden changes in pressure then it could be a concern. I have seen a few odd failures in socket welded joints in hydralic systems that I never would have imagined. The welds looked fine except they were insgle pass caps on 3/8" fillet welds around sockets. Failure were in the HAZ. These MAY have been material related or design related. The piping was subjected to cylcing internal pressure but also had sructural moment imposed because of the way it was supported.

I'm not an engineer nor the son of an engineer but there is some opinion. 10000 PSI hydraulic lines hammering around are nothing to mess with.

[EDIT]That also looks like a heavy land for a backing ring. If I were welding it, Id like a little less land. 0 to 1/16". The gap is good since you need a little room to get the rod in there to melt both edges.
Parent - - By Lawrence (*****) Date 05-28-2008 16:49
Tom,

What are your tollerances for land and gap?.... As detailed, and as fitup....

You might find enough lattitude there to make you comfortable.
Parent - - By js55 (*****) Date 05-28-2008 18:05
Tom,
Not sure what they're getting at with that either. I'm guessin its an old spec that nobody has bothered to take a look at in a long time and it just keeps gettin handed down.
And its actually more perplexing than your comment would indicate, in my opinion.
If there was a concern for toughness you would think that A/SA 106 would not be the choice since this is a material intended for high temp service where toughness is not an issue and the material is generally furnished in the hot finish condition, which means large grain size.
The grain size of the HAZ will not grow much, if at all, its already pretty big, and higher heat inputs will actually tend to expand the width of the HAZ and contribute to a reduction in grain size over a larger area upon cooling. Used this trick in Section III impact testing. Go get big grain materials to beat the UBM with impacts.
And there isn't even a supplementary impact test for this material.
Controlling weave, and perhaps intended heat input, or whatever, seems to demonstrate a lack of understanding of the material of choice.
Now, having said that you will still most likely get decent impacts at moderate temps with this stuff (possibly even fairly low) simply because steel makers are better at their business than they used to be and the stuff is cleaner.
Also, seems to me that if toughness was a concern a better control would be actual heat input.
I'm thinkin the weave limitation is a dinosaur.
Parent - - By swsweld (****) Date 05-29-2008 00:07
I agree. I'm doing military jobs and the specs often get passed down without appropriate changes being made. On a current project that cost us $25,000.00. Ouch!

Seems that there would be a joule range to control heat input if it is a concern.
The root gap is good to go as is. Any wider and the chances for burn through increase.  A natural shake(wiggle) is not a weave ;)
I would do whatever it took to get the root pass in and then run stringers with SMAW if you have to.
The heavy land could serve as heat sink. It could result in incomplete fusion also. Would agree on the 1/16" land as stated by Gerald. We have been using factory bevel/lands with chill rings for a year and no RT rejects to date. SMAW root to cap.

You won't have time to get a RFI answered this time since it takes 2-4 weeks usually with the ACOE but if you have or will have more work w/those specs it may pay to issue a RFI concerning the weave.
Parent - - By 803056 (*****) Date 05-29-2008 01:13
I have to ask what military welding standard is being referenced?

I've worked with a good number of military welding standards and do not recollect any limitations of the width of the weave. They do have limitations on heat input based on the parameters used when the procedure was qualified if toughness is a concern. There are also heat input limitations for quenched and tempered steels, but you are not working with that type of critter.

I hear about limitations on the width of the weave bead all the time, but when I ask where it is written in the welding standard, the tune changes very quickly.

Best regards - Al
Parent - By tom cooper (**) Date 05-29-2008 14:41
That is a good question Al.   I am conveying partially verbal direction from the equipment engineer. The weld spec is Mil-Std-278 and -248.  I have looked many times for where the words "weaving is prohibited" appear but have yet to see this.  Possibly the idea of weaving being forbidden is based on our own PQR's which all cite that "stringer bead" was used for the test plates and consequently "stringer" appears on the WPS's.   I know that AWS D1.1 and D1.2 wants the same info (stringer/weave) listed in their PQR data.  ASME Section IX wants the same info listed, but weave or stringer is listed as "non-essential".       So if our own PQR's show that stringers were used, then I suppose that justifies the "weaving is prohibited" rule.    Or does it? Thoughts welcome.....

My own personnel feeling is that weaving could be a problem for trapping slag or inviting porosity as well as potentially applying excess heat and I know this has all been discussed extensively here.  Welders will weave regardless of what the law says and sometimes like in the root situation that I originally asked about, minor weaving has to be done. So from a practical point of view, I have to admit to allowing weaves "within a couple of diameters" and we generally get along fine. 

As it turns out, the root that I was worried about went well. used a 3/32 rod and small cup and could reach in and sew both sides together. It passed a PT inspection and we went on from there. X-ray is next.

Parent - - By tom cooper (**) Date 05-29-2008 15:28
SWS-
I am interested in how you fit your chill rings to the pipe - how well is the metal to metal contact between  pipe and ring? Ours has never been great, there is always a gap somewhere, sometmes up to 1/16" inch in spots due to pipe ovality. This has caused us great anguish in the past with slag and porosity problems when using SMAW for the root.  I found that the Codes allowed me to use two processes on a single joint (GTAW/SMAW) and so this is the first time we did it this way, hoping the GTAW root would avoid slag & porosity.   I would prefer to find some guidance on how to fit a chill ring. 
Parent - By 803056 (*****) Date 05-29-2008 22:05
You live and die by your WPS.

Best regards - Al
Parent - By swsweld (****) Date 05-29-2008 23:41
Tom, we are welding sch 40 CS preinsulated underground pipe. The code is ASME B31.1. The specs require us to use backing rings for internal cleanliness issues.
What works best for us is to tack one side of the ring near the split with the split near the top. Then position the second pipe or fitting over the ring until it touches the gap pins. If the second pipe has a slightly smaller ID we push the pin together to fit the second pipe.  Then we use a scratch awl or equivalent to pry the split open to get as tight of fit as possible. Then tack the ring on both sides all quarters. Sometimes have a 1/4" gap on the split. That's why I put it on top so gravity is on my side.
The smaller the pipe the better the fits. We had a lot of 14" and had some horrible egg shapes that I was worried about. I would have tigged the roots but all outside and only one experienced tig welder w/RT experience. Me.
I asked the guys on the forum about RT and backing ring after seeing the gaps and it was generally agreed that the internal slag was not an issue for the RT interpreter. After viewing much film I agree.

The fittings to pipe are much worse than pipe to pipe. I D's are different causing gaps but we do the best we can on those but don't counter bore. Our fittings are not RT ed as they are in valve pits but the pipe to pipe welds are. We have some porosity and slag but nothing yet to reject a weld. You may have a more stringent acceptance criteria than we have so GTAW may be the way to go.

The slight gap should not be a big problem if full penetration is achieved. The internal slag doesn't show up only trapped slag in the weld.
Up Topic Welding Industry / Welding Fundamentals / Prohibited Weave on A106 Pipe; also, Better End Prep?

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