Pressure reduction when excavating an ILI feature

[09091960]

Hi,

Despite the defect size standards say that reduction of pressure have to be 80% 0f the MAOP.I belive that pressure
reduction should be based on the size of the defect.Therefore by considering the ILI defect size (based from the ERF value and safe operating pressure) can i establish an equvation to calculate SOP when performing the excavation of a burried pipeline. Appreciate your views on this topic.

Regards,

Ives

 

[SJones]

The term is called 'fitness for service'. The operator has to demonstrate that, by allowing the pipeline to reach 'SOP' (whatever SOP is in relation to MAOP??!), the risk of failure is as low as reaonably practicable, i.e. the pressure-stress-defect interaction is insufficient to cause loss of containment.

You may want to have a browse around here:

http://www.penspenintegrity.com/library/library_frames.html

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[09091960]

Hi Steve,

Thanks for the repond, which opend up a much broad topic of calculating SOP, burst pressure and safety factor for the defects involved.

Regards,

Ives

 

[brimmer]

Check attached to see if it meets your needs. We would aslo reduce the pressure 10% of the highest pressure seen in the last 60 days.

 

[09091960]

Hi Brimmer,

Thanks foe your contribution.The given equation calculates the safe operating pressure (SOP) for a defect. Therefore one have to reduce 80% of SOP when excavating that perticular anomaly?

 

[brimmer]

09091960,

This would depend on your companies policy toward safety. We use the equation or the 10% reduction of pressure seen for the last 60 days, whichever gives the lowest pressure. We do not necesarily reduce to 80% of MAOP (usually these calculations take us below that anyway). Please keep in mind when using ILI data, the data can be out slightly, so your calculations could be out to what is actually there. I would stress always be on the side of caution, you never want to take a chance on personal safety. It will cost you far more in the long run if you injur someone. I would say if your company has a problem reducing pressure by only 20% of MAOP to be safe, they do not consider safety a priority. Also, it depends what kind of defect you are looking at, cracking or geometry anomalies may warrant different rules than corrosion.