Inspection of on site buried natural gas pipeline

[irishal]

Hi,

We operate and maintain a new gas fueled power station in the UK. We have a short section, approx 800 metres, of buried 450mm (18") natural gas pipeline. The gas is at 40 Bar. The line is internally and externally coated and has a sacrificial anode cathodic protectiom (CP) system.

What I want to know is what inspection techniques can be used to ensure the integrity of this pipeline? What would be the minimum accepted from the authorities?

The piping arrangement does not allow for intelligent pigging, or if necessary we would have to install temporary pigging facilities. Also the cost to carry out a pigging run would be expensive in relation to the relatvely short length of line.

Another option to pigging would be to excavate around sections of the line and carry out some ultrasonic inspection but in my experience this could lead to more damage than it is worth.

I am aware of some techniques to monitor the effectiveness of the CP, and unintrusive surveys that can be carried out to detect flaws in the external coating. But my experience of these is limited so any help on these too would be much appreciated.

Thanks,
Irish Al

 

[zdas04]

450 mm pipe at 40 bar with quality internal and external coatings and installed anodes is about as low a corrosion risk as I've ever heard of. Were I in your shoes, I'd write procedures to inspect it internally with a plumbers camera every major plant turn around (4 years? 6 years?).

You didn't say what your flow rate is, but at that pressure you have a really good chance that any flow rate that justifies 450 mm pipe would likely be high enough to sweep any condensation (you need something like 3 m/s velocity).

David

 

[MTPipeliner]

One option you may have is to contract with the natural gas company that delivers gas to your facility. They are likely used to dealing with this kind of facility and the rules that go along with it.

We have several lines that we operate, but another company owns. They don't want to operate it because of their lack of experience with pipelines.

You may not be able to do this, but it's probably worth looking into.

Pat

 

[0707]

Long range guided waves (teletest) can be the option contact Paul Robertson in UK twi.

Regards

Luis Marques

 

[irishal]

Thanks guys. I saw the Teletest method on the web and thought that it looked like a good, unintrusive method of monitoring so we may explore this one in a few months.

 

[Philde]

The normally accepted UK criteria where pipeline is not piggable, (providing you have design/construction records that show fitness for purpose), is an overline survey to validate the effectiveness of the CP. 6 monthly monitoring and 4 yearly survey should satisfy the HSE. The pipeline should ideally have had an overline survey immediately following construction, allowing time for soil stabilisation, to provide a fingerprint, if not get one done asap. (UK cost are around £200/km, + perhaps a premium for a short length).

If you are connected to the UK gas network cycling stresses should not be significant - depending upon where your network connection is(assume you would have allowed for in design anyway if a possibility), internal corrosion should not be an issue either, so providing the CP is effective the pipeline should have a life at least equal to design life.

Phil...

 

[quadtracker]

Try using corrosion coupons installed at various locations in the pipeline, at least it will show any corrosion taking place in the line. Another approach would be to provide a removable flanged section in the pipeline with the same coatings and material as the original pipeline complete with isolation vales and bypass line around the removable pipe section so the section could be analyzed and checked for corrosion on a bi-annual or annual basis. There remote cameras available that can travel a short distance in the line, however the line would need a pig launcher and the line would have to be taken out of service/depressured.

 

[Philde]

Coupons do seem to have come back into favour in recent years, but it has to be remembered that the coupons at best only give an indication of the likely corrosion protection of the pipe. With such a short length of pipeline it should be simple to switch the CP current and therefore obtain an actual polarised potential reading rather than the polarised potential of a coupon and then have to assume the pipeline polarised potential was the same.

The standard 'bible' in the UK is the Institute of Gas Engineers document IGE/TD1. Meet the requirements of that and you should meet the relevant regulations (Pressure Systems Regulations and Pipeline Safety Regulations, the pipeline above appears to fall under both).

Regards

Phil...