Cracking in C276 Casting 1

[weldtek]

We are attempting to repair a 1/2" thick C276 cast cylinder ~ 4' diameter x 6' long. It has seen temperature cycles from ambient to ~ 1400F and operates in a low PH environment.
We received it with a rather large crack about halfway down the length and running about half way around the circumference. When we attempt to weld it, the parent metal cracks 1/2" - 1 1/2" away from our repair. We tried using SMAW with minimum heat input and running beads about 2" long in different areas, allowing them to cool, but, the parent metal cracked on the other side. In other words we were welding on the OD of the part and it cracked on the ID.
Any ideas?

 

[metengr]

weldtek;
Have you verified the chemical composition of the casting as being C276?

 

[weldtek]

Not yet. We don't have in house PMI capability, and I'm waiting on our vendor to get here.
I'll let you know the results from that.
I'm wondering if C 276 in the service described above could be expected to fatigue.
The main crack is about 5' long and the owner says there is a door on the unit at that location, which is opened regularly, and so that area on the cylinder sees a rapid temperature drop.

 

[metengr]

weldtek;
I would be more concerned that the casting was either not properly solution treated or you have contaminants on the ID surface of the cast cylinder. The C-276 material exhibits excellent weldability using GTAW and SMAW processes. If the chemical composition meets the requirements for C-276, I would look to an improper solution anneal heat treatment from day one or some type of surface contaminants. Can you extract a small boat sample containing the ID crack and send it out for metallurgical analysis? This would confirm alloy ID, identify the nature of the ID crack, and provide information as to the alloy microstructure.

 

[unclesyd]

I'll echo metengr's post on the weldability of C276. In fact it in itself is a very good welding electrode.

Could you clear up a little information in you first post.
You state that it sees a temperature swing of 1400°F and then you state that the crack was in the casting as received.
Is this new casting or an in service casting?

If in service high often is the heat cycle and the times at temperature?

 

[weldtek]

Metengr, as far as contaminants go, I asked the owner for information as to the service environment, and he said there was a low PH and high temps, but no significant contaminants. We have ground the material edges and solvent cleaned them. What about re solution treating, would be likely to help?
Unclesyd, this casting has been in service, to the best of my knowledge, a year or so. We used to fabricate this part for them, out of C276 plate, and they would last about a year, so, several years ago they went to a casting, and they say that has extended the life of the part to around 18 months.
I'll have to ask them for more specific info re: times at temp.

 

[metengr]

weldtek;
I don't want to get to far ahead and lead you down the wrong path, but the more I think about your situation the more you need to remove a material sample with a crack for better diagnosis (if the chemistry confirms correct material). This analysis can be turned around quickly and will provide information regarding permanent repairs. Good Luck

 

[weldtek]

Thanks for your input. We're still waiting for PMI and I'm going to suggest that we remove a sample for testing as you recommended.

 

[metengr]

Don't forget to let us know your results and follow-up. I am interested.

 

[EdStainless]

Even small amounts of S in the weld can cause some serious cracking.
What is the acid? Much F in the application?

But, I tend to believe that my senior brothers hit this one, that this part may have some more fundamental problems. Like composition and microstructure.

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[weldtek]

Field PMI indicates the material to be C276. Would you expect cast material to be significantly different from wrought in terms of weldability?

 

[unclesyd]

I haven't seen any problems on numerous cast components we had in service. The majority of parts were cast rings machined to make studded outlets for a C276 vessels.

Microstructural analysis of the sample will provide a some much needed information.

Are there any very small cracks on the OD of the casting besides the large crack?

What type casting is the shell?


I'm trying to find some old brochures on Hastelloy 276 where they talked about C276. If I recall one of the benefits of the C276 material was the improvement in weldability over 276.

 

[dutchmat]

The problem with C-276 castings is the wide specification of certain elements. If casted well, it even survives the standard corrosion test in the "as cast condition"

Brochures of C-276 are not going to help you much, because structure and purity of the rolled material can not compared to the as cast material.

The quality of the cast c-276 depends on purity of the metal and most important carbon content, as low 0.015 or lower!

It goes a bit to far to go deep into this matter, but I am afraid that your casting maybe is in the spec of c-276 castings but full is with impurities and has on top of that a high carbon content.