Problems welding thin wallthickness pipe 1

[alomejorfofi]

Hi,
I am selecting the specification of a pipe system for cooling a nuclear experiment. The material you selected by the characteristics of Fluids is stainless steel A312 Gr 316L TP for various diameters.
Several colleagues with experience on the site, have warned me that buttwelding pipe with 'large' diameters (18 ", 10") with thin thickness (sch-10s) can cause technical problems, and many headaches.
I have to decide between lower costs of supply and erection, but possible technical problems when welding.
I would like to know what you think people with experience in welding.
thanks in advance

 

[metengr]

Several colleagues with experience on the site, have warned me that buttwelding pipe with 'large' diameters (18 ", 10") with thin thickness (sch-10s) can cause technical problems, and many headaches.

Warpage will be an issue. I would suggest using the GTAW process and keep the interpass temperature less than 325 deg F. Watch your start and stops.

 

[chicopee]

Brazing may be a better option.

 

[Duwe6]

Pulsed GMAW is the other good choice for Nuke grade welds.

 

[EdStainless]

Alignment is the biggest problem with these large sizes in light wall. A good system for clamping the pieces to hold them straight is important. They will distort during welding. You have to let them move some.
We see a lot of people use sch40 in places where sch5 will meet the design just because they don't want to do the work.

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Plymouth Tube

 

[alomejorfofi]

thanks guys!

greetings

 

[rmw]

And, the light gages and larger sizes, Sch 10 & Sch 20 in those sizes can be known as "unobtanium" grade, especially in seamless if that was what you were going for. Std wall (watch out, Sch 40 in the sizes above 10" is thicker than std wall) is much more easy to source. Af you are using anything other than std wall, you either have to find (see 'unobtanium' remark above) and use corresponding schedule wall fittings, elbows, tees, flanges, etc., or bevel each fitting for the mismatch in I.D. between std wall and your pipe schedule. Your "savings" can easily be wiped out due to problems sourcing light schedules. Been there had that happen to me.

If you are using ERW pipe, it can have ovality problems that become part of the "work" Ed Stainless mentions above. I for one am in the world he describes. Light schedule pipe creates more problems than it solves.

If this were to have been a highly exotic alloy grade, Duplex or Hastelloy for example, you'd have to use the lighter gage due to cost difference, obviously.

rmw

 

[EdStainless]

At these diameters this will be welded pipe.
You will need to be careful sourcing it.
For ease of welding the welds will need to be planished flush on both ID and OD.
For good corrosion resistance it will need to be fully furnace annealed.
And then they have to make it round again.
This is custom fabricated pipe.
If the aerospace guys can butt weld 4"x0.032" wall then you can weld this.

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Plymouth Tube

 

[MiketheEngineer]

Unless you are buying miles of pipe - just use schedule 40 or better. Since this is nuclear - YOU DO NOT WANT any problems - because if you do - S&&t will hit the fan so fast you won't even see it happen.

One tiny leak will shut the plant down and some little old lady that lives 20 miles down the road will want to sue over radiation sickness.

 

[alomejorfofi]

I am waitting for the quotation from suppliers, so when i recieve it i will see if there are fittings with this schedule in stock and their prices. Then, the proposal manager will question me about my technical evalutaion, and then...........i say that in large diameters like 18", 16", 14", 12", even 10" i don't recommend use thin walls because:
-possible no disponibilty of fittings, or high cost
-alignment & ovality problems
- we don't know if our assemblers can weld appropriately this pipes

anything else?
will see

 

[moltenmetal]

Wow, you guys must be made of money if you're going with sch40S at these sizes just to make the welding easier! That may well be the right decision in the nuclear industry, but if we made those sorts of decisions in our industry we'd be out of business.

As long as you specify (and can tolerate) welded seam, the fittings and pipe are no problem to come by, though it appears that what suppliers send us are often sch40S fittings that were a little under-thickness: they have been back-prepped on the ID to take them back to sch10S thickness. Those need to be checked carefully before use or you may have problems with RT later.

Preparation for butt welding takes some time and some tooling, but the welding itself takes fewer passes. People that make thin-wall stainless vessels have it way harder. Find a competent weld shop and they'll do a great job for you.

It can look a little ugly if the deposition rates are too high- you do tend to get a bit of diametral shrinkage.

Make sure you don't use 3000# o-let fittings for branches and then expect the welder to completely fill the bevel. You will end up with a sausage, and for no reason. There are better alternatives available.

 

[MiketheEngineer]

In the long run or even the short run - you don't screw around with nuclear. Matter of fact - my company made a conscious decision to stay AWAY from them. We could never make money, the safety issues were nuts and way too many people to enforce them, our equipment could never get completely decontaminated and so it never - ever left the plant.

What does it say about our people?? Some seem to glow at night!!

 

[stanweld]

We weld Sch 10S stainless pipe in the field as a matter of course and regularly meet radiographic quality requirements. We do the same for repairs of vessels and tanks. Without using extra low carbon stainless grades or employing rapid cooling techniques during welding, sensitization is inevitable. Some distortion is also inevitable; distortion can be mitigated using short circuiting or pulsed transfer GMAW.