Pipeline Derating 1

[suraiya]

Is there any standard/best practices/rule of thumb exist on how to obtain a pipeline age derating factor?

I'm currently working on an old (15 yrs) subsea 18" crude oil pipeline which need to be revived.

I understand that the best way is to do physical inspections, which might include intelligent pigging etc, but all I need is some first hand idea for high level feasibility studies. Physical inspection might be too costly for this purpose.

rgds,
suraiya

 

[DSB123]

suraiya,
I do not understand how you expect to derate the pipeline when you do not know the condition its in. You need to know the minimum actual thickness of the pipe, if it has any forms of defects such as local metal loss, gouges, dents and most of all what the corrosion rate is. From this actual data you can then proceed to assess the line and possibly derate if thats possible. You may find that the defects need to be repaired etc. API 579 will help. BUT MOST IMPORTANTLY you need to know the actual condition of the line.

 

[zdas04]

Run the smart pig. Any "age deration" factor (if such a thing exists) would have to have assumed some rate of internal and external corrosion that is very fluid and environment dependent. Since you just don't know if there has ever been an anchor drag over the pipe or microbes inside the pipe I would never recommend returning it to service without a detailed in situ evaluation.

The good news is that those sorts of tests just keep getting less expensive and more capable every year. If you're considering using the line you can be very confident that assessing it will be a tiny fraction of the cost of replacing it.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[pmover]

suraiya,

short of obtaining actual pipeline data (smart pig) & for your initial high-level feasibility analysis, make an assumption to fit the proposed pipeline conditions. be certain that all essential personnel know the assumptions used. however, the assumptions used should not exceed the original design conditions for pipeline undergoing analysis.

furthermore, i am not familiar with an age derating factor for pipelines. hence, the reason for obtaining pipeline data via smart pig. once the smart pig data is obtained, engrs can determine pipeline integrity and then use industry stds to determine pipeline ratings.

also, should this feasibility study result in further action/analysis, the need for smart pigging the pipeline may be warranted.

good luck!
-pmover