Hastelloy weldability 5

[asv80]

Hi,

Can hastelloy (C276 or C22) be welded to stainless steel (304L or 316L)?

We need some directions on what process can be used and if it has been done before.

Thanks in advance.

 

[EdStainless]

Sure, the welding is no problem. What weld properties do you want to end up with? Typically you would use the high alloy filler material for these welds.

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[asv80]

EdStainless:

The welding is required at the area of tubes joining tube sheet in a condenser.

What methods and filler metal can be used to weld?

I did not follow what you meant by the final weld properties. The welding is required to seal any gaps and prevent leaks after the tubes are expanded.

Thank you.

 

[unclesyd]

Even though it's is quite a bit more expensive I would use the C276 filler metal using either an automatic tube welder or GTAW.
We have used both methods along with an autogenous weld between the tube and tubesheet.

We often use your combination either in a full bundle or using the C276 as a safe end material for SS.

 

[EdStainless]

Why are you welding the tubes? Severe service? Large temperature swings? Make sure that you really need to weld.
Syd is right, it should be done automatic.

What size and thickness are the tubes? If you are only looking for sealing then just do it autoagenous.

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Rust never sleeps
Neither should your protection

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[asv80]

The weld is a requirement for clean service with no crevices allowed.

We are not sure about temperature swings.

Tube size: 1/2" 20 gage, 3/4" 22 & 18 gage mixed

 

[metengr]

I would suggest you conduct a mock-up (simulation of a tube to tubesheet weld joint) to assure familiarity of the job. If the tube welding is not performed correctly you will have problems. I would also suggest a leak test or perform a liquid penetrant examination of the tube seal welds.

 

[unclesyd]

Your tube gage is quite thin so welding will be tricky. I would definately try to do a little mock-up as suggested above not only for the afore mentioned reasons but also to checkout the procdure.

I would definately try to go automatic due primarly to the thin wall tubes which will require the undivided attention of a welder using a manual process. If you have too you can rent a an automatic tube welder

Every tubebundle, over 200 alloy and 50 or so CS, on our site is rolled and seal welded. I don't remember every having any problems on new fabrications. The only problems I've seen has been contamination during a retubing that caused some minor weld problems.

 

[asv80]

We are going to prepare test welds to make our welders comfortable with welding these materials. They have welded hastelloy before only not to stainless.

The joint is almost always done with automatic welder.

Also we need to get a procedure qualified as well. Hopefully it would go without much trouble.

Thank you for all your inputs.

 

[EdStainless]

I still wonder why they are beign welded. I see light gage stainless tubes (walls from 0.020" - 0.028", 0.750"-1.5" diameter) rolled into rough holes (not grooved, but not smooth) a lot. Push out strengths for these joints are often over 4,000#. If you need the seal fine, but if not why bother?

Very light gage tubes (0.012"-0.018") are usually welded because you can't get strong enough roll joints. I have watched millions of tube ends in 3/4"x0.016" tubing welded using automatic machines.

When tubes are going to be seal welded, often the tubes are installed and lightly rolled, just enough to bring the tubes in contact with the holes. Then they are welded and inspected (dye pen and/or leak tested). After that the tubes are then hard rolled.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

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[stanweld]

In addition to the above excellent advice, I recommend that you instruct your welders to not "TIG wash" the weld after deposition to make it more cosmetically appealing. I have seen welders use this technique (essential variable violation)with hot cracking consequences on sililar tube-to-tubesheet welds.

 

[EdStainless]

I'll add a bit more claification.

You do not want to hard roll the tubes prior to welding.
- It can lead to blow holes from traped gas/moisture in the joint
- It is very difficult to leak test the weld, and only the weld

You must hard roll the joints after welding.
- You need to be careful to stay away from both faces of the tubesheet, rolling the welds can cause cracks, rolling to the back of the tubesheet can cause tube problems
- You need the tubes well supported. If they are 'loose' in the holes and only welded at the front you can get vibration and the tubes rattling in the holes. They fatigue quickly this way.

You must have mock ups that are destructivly tested. And no re-welding unless a joint fails leak test. You don't care if they look good, you want them to work.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[unclesyd]

One thing not mentioned is the problem you may encounter with C276 in work hardening as you attempt to roll/expand the tubes. The light gage tubes will certainly exasperate the problem as the tube will tend to walk in front of the tube roller. On some 14 gage C276 tubes we had to go with parallel roller instead of the normal taper roller. It took numerous tests to achieve a good roll.

If design conditions permit you may want to consider a weld only tube/tubesheet connection

As posted by EdStainless a test setup is an absolute must.