Getting remaining life 3

[Hansac]

A piping has an external localized corrosion. The remaining thickness measured is (example) 5.3 mm. The minimum required thickness as per B31.3 is 5.4 mm. The flaw passed ASME B31G (i.e. maximum allowable pressure for flaw is greater than design pressure of piping).

My question now, is how to determine remaining life? B31G does not provide this. And if I work backward for the given pressure by B31G, I don't think I will get a lower minimum required thickness. I need some meat so that I could put that in the corrosion allowance, so that I can have some semblance of remaining life.

Any suggestions?

 

[metengr]

Yes, why don't you locally weld repair the thinned area if it is on the OD surface????? This could be the simpler approach and is permanent.

 

[Hansac]

Metengr:

I am looking for something for non-repair approach, for now.

 

[metengr]

Hansac;
Is the pipe limited by time dependent properties (creep)? If not, you can argue that your design margin will be slightly below what is required by ASME B31.3 in a locally thinned region, but you still have the surrounding pipe material to carry the service stresses provided you taper the ends of the thinned region to minimize stress concentration.

Off the top of my head, I would seek guidance from either API 579 Fitness for Service or even ASME Section VIII, Div 1 in one of the Appendices (can't remember which one at the moment) to assess locally thinned areas (LTA's).

 

[Hansac]

metengr:

I am thinking of using factor of safety 2.7 instead of 3.0 as used by B31.3

I am consulting 579 now and will look in Division 1, later.

Yes! I know I can use Division 1 for piping because I am an engineer! Hahahahaha.

 

[Hansac]

And no, it is not affected by creep. It is a well flow line for crude oil in an oil platform. Temperature should be below 200 or 150 degC. It is carbon steel, of course.

 

[DSB123]

Hansac,
API 579 is the way to go. You can determine the FCA (Future corrosion allowance) left and hence the time left until the LTA must be repaired.

 

[LSThill]

Technical Note:

State of California "Integrity Management Law".

Mechanical Integrity: API 579 – ASME FFS-1 FITNESS FOR SERVICES publish Standard June 2007


Technical Note: Review this option:

http://www.paulin.com

Chapter 5 – Section 1 Nozzle/PRO Fitness for Service

Local thin areas and crack like flaws may be evaluated for most Nozzle/PRO geometries using the Nozzle/PRO fitness for service input form. Fitness for service evaluations are conducted using API 579 – ASME FFS-1 FITNESS FOR methodologies for Level 2 & Level 3 checks. Up to ten flaws may be defined for each model. To access the fitness for service options, click the “API 579 – ASME FFS-1 FITNESS FOR” icon as shown below:



L S THILL

 

[jte]

Hansac-

B31.G, the Manual for Determining the Remaining Strength of Corroded Pipelines does not explicitly state how to determine the future corrosion allowance. The API-579 approach is a bit more clearly spelled out since they include FCA in their equations, but there is nothing that says you cannot apply FCA to a B31.G approach. Simply add another mm to the depth of your pit and re-run the numbers to see if the pit passes. Iterate until it fails the evaluation.

jt

 

[Hansac]

jt:

Now why didn't I think of that (manipulating B31G in that way?)?