Rotating Equipment - Polyethylene erosion on steel shaft

[awhicker84]

Hi all,

Reference thread:

http://www.eng-tips.com/viewthread.cfm?qid=63814

We have a machine that is eroding in one area of the shaft. The process is mostly ethylene. The erosion caused a radius cut in a step area of the shaft such that material is being taken away in a J shape and the diameter of the shaft at the location of the erosion is about .600" less than OEM.

We have to bring the shaft back to dimension. The shaft is Carbon Steel (A668). Options that seem reasonable to me:

1) Weld repair with Carbon Steel, HVOF with xxx to reduce possible erosion in future.
2) Weld repair with Inconel (or xxx)

The thread I linked above calls out ceramics as well. I have no experience with ceramics or how they are applied.

Our shop is located in Houston, TX.

Cheers,

 

[awhicker84]

It should be noted that we have an aluminum laby seal (non-rotating) that has a small clearances against the vertical wall (rotating). I did not design this, but I'm assuming this exists to reduce the chances of our erosion issues. This design is non-std.

I do not know what the aluminum seal looks like at this point. I only know what the rotor looks like and it is heavily eroded. Another possible solution may have to do with the laby seal material. However, if the two surfaces rub, the seal should be sacrificial. Galling is unacceptable.

I am keeping my question to material choice only. I will solve any other issues.

 

[EdStainless]

What steel is the shaft? (actually what C) Will you need to re-heat treat it after the weld repair?

I have used both ceramic spray and carbide overlay in wear applications. I prefer the tungsten carbide, it is denser and adheres better.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[awhicker84]

It is A-668 Class D.

It's an interesting choice of steel given that nothing is specified on the chemical req's except: Mn, P, S. However, we limit our carbon content to 0.35% per S4 of the ASTM spec.

 

[awhicker84]

As far as PWHT, I'm trying to pull the mat'l certs and see what temperature we tempered at. We will base the PWHT off of that if we weld repair with a WPS for carbon steel.

I will have to talk with weld engineering if we do anything that inconel overlay. I'm not sure what type of heat treat would be required for something like that.