Repairability of CA6NM

[mahadhatu]

I am trying to determine the end of life for some CA6NM pumps in H2SO4 service. We have repaired these pumps numerous times. I am looking for ways to tell when the pumps cannot be repaired any more.

Thanks for your comments.



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There is always some thing better out there...
Mahadhatu

 

[metengr]

mahadhatu;
Because of the thermal treatment requirements for CA6NM castings, my advice would be to run some portable hardness checks of the castings, if in doubt, to make sure they are within specification.

If you perform nondestructive testing (NDT) prior to and after weld repair, this should suffice. Castings can be weld repaired many times before either repair costs exceed replacement costs or the increase in repair frequency results in too much equipment downtime.

 

[arunmrao]

I have repaired worn out CA6NM buckets on a Pelton wheel. This is a standard practice to salvage the life of the wheel and extend its useful life.

Are you repairing the volute or the impeller ?

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

 

[mahadhatu]

The impeller is usually replaced depending on the amount of damage on it.I am repairing the Volute and the head. These items are badly damaged and had to cast pieces of the volute and the head and weld them on the worn pieces. This cost was still lower than a new set.

We will perform NDT - X-ray of the repaired areas and then a pressure test.

Can this base material be metallurgically stable after multiple repairs?

Arun do you keep track of your repairs on the pelton wheel? and how do you decide that it is time to replace instead of repair?

Thank you

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There is always some thing better out there...
Mahadhatu

 

[arunmrao]

My services have been employed as an external contactor to carry out weld repairs. Dye penetrant testing and hardness were the two parameters checked.

I do not see any issue if you decide to continue weld repair the volute,until its logical end. Pressure testing is not a major issue in volutes as compared to valves.

It is good that you have been able to cast pieces of the worn regions and then matched it across the volute and welded.

Please check for any welding cracks and hardness.

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

 

[mahadhatu]

I guess my question also is how do you determine if the base metal is metallurgically stable after continued repair and being in service for extended length of time.



--------------------------------------
There is always some thing better out there...
Mahadhatu

 

[metengr]

mahadhatu;
You really don't need to evaluate the base material unless problems develop either during or after weld repair, which is the reason for performing post weld repair NDT. The pressure test you mentioned is also an excellent idea to assure structural integrity of the repaired castings.

 

[arunmrao]

I agree with metengr's comments about the base metal properties remaining unchanged. It is only the weldment that needs attention.

I like your attempt at conserving resources,by repair welding rather than indent a new one.

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

 

[EdStainless]

How large are the parts, and how much is being welded?
If you are heating a large amount of the metal, and you are concerned about corrosion resistance, then maybe you should look into re-heat treating the entire part.

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Neither should your protection

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

 

[mahadhatu]

Ed,
The pumpcase is 48" diameter. The welding being performed is major. As I mentioned before, I had to cast pieces and weld them on to the case. These pieces were fully heat treated and I intend to do a double temper heat treat after welding to preserve the corrosion resistance of the base amd the new metal. I believe this should suffice to maintain its metallurgical stability.

Thank you

--------------------------------------
There is always some thing better out there...
Mahadhatu