Determining the wall thickness of buried steel pipes

[Mike93]

Hello everyone,

Is there a way to determine the wall thickness of buried steel pipes in a natural gas distribution network?
Gas distribution network can be 20,30,40 years old (corrosion is a factor) and 5 to 80 km length. The length of pipes may vary from 10 to 2000 m and diameter from 2" to 4" mostly.
Pigging I don' think it can be an option due the pipe branching, curves of the pipes (e.g. it can be angle of 90 degrees), T branches etc.
Ultrasound can work theoretical but is not suitable for distribution due the above reasons. The signal of a transmitter go straight so it will be lost at first angle. Mounting on every angle a transmitter is not cost effective of course and also digging/making holes for mounting will not be possible because local authorities don't approve.

Hope I didn't say something stupid. I'm new in this field.

 

[LittleInch]

Small non piggable distribution systems are virtually impossible to inspect.

However pressures are usually very low and at small diameters only need paper thin steel to survive unless someone digs them up.

Why are they steel? Most distribution systems nowadays would tend to be ductile iron or Poly Ethylene (PE) for these reasons.

At 40 years old you probably need to be thinking about replacement or internal lining.

You can look into the old risk based inspection / replacement ideas where you wait until section start failing or you identify sections where if it did fail it would put a lot of people at risk.

What does your regulator say about these things?


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Mike93]

We replace them with PE. But still there is a lot of steel on gas network.
We have already prioritized based on some criteria. One of them and I think the most important is number of insulation defects.

Thank you for your answer.

 

[LittleInch]

If you have coated pipe and CP then you can do some pretty cheap surveys on the coating defects, especially DCVG highlights individual defects within less than 1m, but it depends how well you can isolate sections and what the level of interference and coating damage you have.

Other than spot checks on individual locations to determine spot wall thickness there's no magic device I know that can do that level of inspection over those sorts of lengths.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Mike93]

Yes, pipes are coated and also some of them have CP. Current issues and the challenge for us is where we need to use galvanic anode because we never use it. But that's another topic where I would make it in Corrosion enginnering part.