Pipe thickness

[gtwy]

We have a municipal client who had a catastrophic piping failure several years ago in an underground vault that caused flooding and major damage to the motors and controls. The failure occurred in a 25 year old 10" cast iron pipe tee feeding three pumps. The tee had probably been leaking to the extent that they had time to replace it, had they understood the urgency of the situation.They are currently reviewing their operating procedures for events like this and my only involvement is in the controls and alarms for the system. They have since located the controls to grade.
I have no experience w/testing piping and vessel systems or the methods used. I do a lot of work in oil refining where radiography seems to be a way of life. I was curious as to whether they might give thought to some sort of periodic testing of their piping systems- is there some other economical thickness testing equipment available.
This municipality is more or less a bedroom community of about 12k but has a large auto plant and some other commercial developments that use their waste and potable water systems.

 

[metengr]

The problem with cast iron water pipe is not corrosion and loss of thickness. Instead, the problem is ground shifting or vibration that results in fracture of the cast iron supply pipe. Trying to perform thickness testing will not yield the type of results that can ensure no failure in service.

 

[metengr]

Just a clarification on my part and not to mislead you into thinking cast iron pipe will not corrode. There are cases where cast iron water supply piping will indeed corrode from stray currents, biological activity associated with soils and water quality. However, in most cases failure typically occurs from the two factors I mentioned above. If the previous pipe failure was caused by corrosion, thickness testing can be done using ultrasonic thickness testing if the OD of the pipe is accessible. If the line is buried, internal thickness can be done using a smart pigging device that requires the line to be out of service and drained.

 

[gtwy]

Thank you for the reply. The tee is close coupled between the concrete wall and the pumps- I can see where cracking would be an issue. Just curious if nothing else for future reference what might be available by way of wall thickness testing. Instrumentation that the client might purchase, or is that out of the scope of what a small to medium municipality might be able to purchase/operate?. More than likely better attention to detail on there part would go a long way, at least on exposed piping.

 

[11echo]

Using cast iron pipe is "old school" ...yes it corrodes, but like aluminum that corrosion helps protect the rest of the casting, and is why you see a lot of water handling equipment being manufactured out of cast iron (that and ease of machining the metal). The other issue is joint type, using cast iron you don't weld it together, you use mechanical couplings ....dresser coupling, Victaulic couplings, & etc. These days for running water handling pipe I'd suggest H.D.P.E., PVC, or similar plastic pipe. The material cost is much less, and pipeline fabrication goes a lot faster, and under normal conditions corrosion is a non-issue. FYI ...you can even do a half-n-half ...replace the bad section(s) of cast iron and use the same mechanical couplings to mate to the new "plastic" section!

 

[gtwy]

I am not sure of the physical layout, but the "vault" is adjacent to or part of a wet well at the auto plant. The pipe is embedded and protruding horizontally near the bottom of the well into the vault area. It is close coupled to the tee which feeds three 50 HP pumps. How would the pvc mat'l hold up if it were a vibration issue?

 

[11echo]

You could use flex-couplings at pumps and design in some flexibility to the piping configuration to handle any normal vibration issues.