bulge in piping need repair 1

[smart143]

We had fabricated a piping spool according to b31.3 code. Header A358 316L & size was36"x 8 mm with a pair of 2" ss latrolet welded 180 apart in set on condition.
While keeping the latrolet alignment during welding they bulge inside pipe id by 5 and 7 mm.we used jacks from inside of pipe to minimise the bulge.post fabrication area around each latrolet is also gone down by 5 to 6 mm.I place straight edge on pipe OD near latrolet, i can see this deformation to tune of 5-6 mm

Now customer is not ready to accept this unit stating that pipe A358 316L which we used is not in alignment with its dimensional requirements.

We explain customer that before start of fabrication pipe was within straightness of 3 mm in 1000mm. But after latrolet welding this deformation has occurred and should not be considered as cause for rejection. Customer is firm on his stand as no matter what kind of fabrication we did, pipe should maintain his straightness during fabrication and suppliers should take adequte measures to counter this during fabrication.is this stand of customer is correct,Can we challenge to this rejection....drawing did not specify anything about bulge allowance .

If we have to rectify this bulge/ deformation, can we use haeating option for repair...is it a correct way of doing correction on austenitic material...we r in trouble and need help

 

[Dougt115]

Ask the customer. The bulge may not matter but the straightness may be critical to their needs.

From doing quality assurance the only values that they can reject the parts for are the ones that they specified on the drawing. If they don't like the bulge then they will have to pay. But straightness they did specify so you are stuck. If you try to hold them to this you may lose a customer.

IF they add removing the bulge as a requirement then you may need to add cost to prevent it.

How to fix what you have?? No idea from what you have stated.

 

[smart143]

Hi Dought115, Thanks for your quick response.

Customer did not specified straightness requirement on his drawing, drawing calls out material of header spool as A358 316L.
A 358 specification calls out straightness requirement as 3 mm in 1000 mm. we procured pipe which was well within this requirement, infact the straightness was within 0.5 mm in 1000 mm. However when we started welding Latrolet on it, the straightness was compromised due to bulge. Customer stand is that now the present condition of spool pipe is not meeting straightness requirement of pipe.

I am of opinion that straightness requirement on pipe is no more valid as it has been further fabricated into as spool piece & fabrication distortion may play into it. So there should be some tolerance for distortion & straightness post fabrication on piping spool drawing, currently its not there. So we are fighting against this, is our stand correct or customer is right per code.

Alternately I am trying to propose an option where we can locally heat the pipe(by flame heating torches) & use internal jacks from pipe ID to uplift the area around nozzles so that straightness of pipe is regained to within acceptable limit of 3 in 1000 mm. Can this localized heating affect the mechanical & corrosion resistance properties of austenitic steel, is it a correct way of repair or I shall do some thing else.

 

[LittleInch]

Ok,

As I understand this you have a very thin pipe (D/t of 115) to which you are welding a latrolet. During this procedure the pipe has bulged inwards by 5-8mm. Has it affected the actual straightness of the pipe, i.e. is it bent like a banana or still very straight from end to end apart from where you have welded the connections? Pipe this thin is notoriously difficult to weld and keep it all straight. Is this your first time with this size and thickness?

If it is still straight then I think your customer is being rather obtuse about this and not seeing the big picture about whether this minor depression is actually causing any impact or not. If the pipe is piggable or for some reason needs to be very smooth and straight then I can see their point, but if so then this should have been made clear it the scope and specification / drawings.

It seems you have a few options:

a) Cold work the "bulge" with jacks or other devices - heat is not a great idea on this material
b) Cut out the section and weld a new pup piece in with the latrolets, but this time re-inforce the internal ID and restrict the amount of heat into the weld as much as you can
c) Argue with the customer

PS - A picture would be great to see what we're talking about here...


My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[gerhardl]

The requirement for straightness might have several purposes. One is of course the straightness according to flow carachteristics and clogging/cleaning. A more wide purpose, although not expressed directly, is to assure an overall higher quality. In this respect any material deflection, however slight, given after welding, might indicate an improper welding procedure and/or a possible starting point for material weakness in the future.

In engineering we often see claims as yours, expressed as 'we are just a tiny bit over the limit, why can't you accept this?'

For cases where the limit is expressed as an absolute limit (for instance a pressure class limit), the answer is strictly no.

In your case it seems that you are above a given limit. How absolute is this limit, and why? It could perhaps be a way out if the customer could agree to repair and test procedures proving that all will be ok also for longtime application.

If the customers do not agree, I cannot see any arguments you could use.

 

[MJCronin]

What does ASME B31.3 say about the straightness and ovality of pipe spools ?

How about the EN 13480 standard ? Is it more or less restrictive ?

Is the customer asking for requirements that are above and beyond the requirements of either piping code ?

Does your company have any experience working these high D/t pipe spools or is this the first one ?

Photographs or sketches would certainly help here....

MJCronin
Sr. Process Engineer

 

[Dougt115]

Your customer specified the material, A358 316L, meaning to me that straightness of the end product is important. Otherwise why did the specify the material to be A358?

They will likely reject any parts you deliver that do not meet the straightness of A358.

 

[3DDave]

The Material spec only applies before fabrication. For example, in the weld area it will no longer meet the original alloy requirements. If the final item drawing doesn't specify dimensional requirements then the drawing is deficient. Good luck with this customer. They did not evaluate their real requirements and are just going off a catalog (spec in this case) value.

On the other hand, it is possible a different welder could be of benefit or a change to the weld size. Putting a fat weld on is sometimes seen as a better weld, but it is just more material to shrink when it cools leading to more distortion. One supplier I worked with had a terrible time with an 'impossible' design that we'd already made close to a hundred of. We found the original welder, got them in contact, and they let us know that our guy was much, much faster, the distortion was much less, and the parts that were 'impossible,' fit together just fine. Their welder was a USAF qualified aircraft repair guy, so no slouch, and the welds were sound, but he just used the fat-weld concept. I suspect he learned a lot from the old guy.

 

[weldstan]

One of the few in service failures at the Prudhoe Bay facilities at similar thin wall stainless steel branch connection was due to a similar inward bulge. If the out of roundness at the branch exceeds B31.3, it must be replaced. When making this weld in the future, the branch should be positioned at the run pipe's 3:00 position - not at the top or bottom.

 

[smart143]

We did recover the straightness by using inside jacks with cold work.now the straightness of pipe around nozzle weld is within 3 mm.it seems customer will accept this repair.
Thanks everybody !!!

 

[marty007]

It sounds like you've managed to make something work to make the customer happy, good work.

As for code requirements, I would agree with 3DDave. The material spec only applies prior to fabrication, and any restrictions on distortion post-fabrication should be stated on customer contract documents.