Corrosion Rates for Shaft Piping

[ChristopherFehr]

We are looking at changing out some shaft piping in one of our wet head frames. The problem is the mine will only be running for another 3 years. Does anyone have any literature on the expected corosion rate for pipe in this environment? The pipe has lost 8 to 30% of it's original thickness but it has not been very well documented if any was changed from original in 1966. Does anyone have experience operating a pipe that has reduced thickness below ASME B31.1 thickness?

 

[CanuckMiner]

ChrisopherFehr,

I am sure you realize that this is a very global question with a very site-specific answer (or answers). Having said that I offer the following comments, for what they're worth.

We went through an exercise a few years ago on behalf of a client to evaluate the piping in one of the shafts. This was for air, water, and pump line I believe (I'm going from memory here as I do not have the report at hand).

The client had measured the wall thickness of each (or, more likely, nearly each) length of pipe in the shaft. We then went through the calculations to determine how much wall thickness was required for the pressure. Next, we calculated how much "excess" wall thickness was remaining, and could be considered for corrosion allowance.

What we developed were a few recommendations. For some regions within the shaft, we recommended replacing the pipe as soon as possible (on an off-shift) as the calculated available corrosion allowance was negative (Yikes!). For some regions where the corrosion allowances were still quite high, there were no requirements to replace the pipe. It was those "in between" pipes where the calculated corrosion allowance (available) was "moderate" that some judgement was required. I can't recall offhand if the client had kept records of when the pipes were installed, but if so, that may have served as a method of estimating/extrapolating how much time they had left. I recognize that you do not have the luxury of such records at your operation.

I also asked some of my senior colleagues who cited a few case histories. Mines that have been in operation for more than 25 years, and only now are considering replacing pipes and shaft sets (steel). I then received a brief lecture on the variables, including: fresh air or exhaust in the shaft?, type of orebody (e.g. sulphides?), original corrosion protection on the pipe (enamel paint, epoxy paint, galvanized, etc.), wetness of the shaft, etc.

I will see if I can find the report I mentioned and if there were any valid figures, I will post them.

If you come across any figures (from technical papers, etc.), please post them, as I am interested in this too.

Cheers and Good Luck,
CanuckMiner