Piping Wall Thickness Calculation

[nd222]

Hello,

Original wall thikness of 28" column overhead line was 10mm. The pipe material is ASTM A 672 GRB60 CL12. After 20 years of operation the inspection has found the wall thickness reduced to 7.8mm and recommends for replacement of the line in next plant Turn Around.
The calculated wall thickness as per ASME B31.3 of the 28" line using design condition is 5.3mm (including 3mm CA).

As the available thickness of pipe is still more than the required thickness as per calculation, can we retain the same line or is there some other points that has to be considered in deciding the action plan. Please suggest.

Thanks

 

[LittleInch]

My guess is that originally someone looked at 9.5mm (10 isn't a standard wall thickness)which is also STD wt and decided a D/t factor of 75 was thin enough for practical purposes. If the design wt for pressure is only 2.3mm this is presumably pretty low pressure, but then practicality comes to the fore. D/t of between 90 to 100 is normally the highest people want to go.

Now that its built some on these issues go away, but structural strength and stress analysis would need to be addressed to confirm that your 7.8mm is ok.

Is this reduction in wt uniform or is this the lowest in a pitting sense?

You could review ASME FFS-1. latest version 2016 for fitness for Service calculations and assessments.

All depends how much it costs to replace. You could just replace it at less cost that it takes to have someone do the work which might say you still need to replace it...


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

 

[KevinNZ]

I agree with LittleInch, you can not just look at the thickness required for pressure. You need to look what else the pipe wall is doing, The pipe needs strength to hold it self up and resists wind and EQ loads. Large diameter pipe may also have high local stress at the supports.

 

[mk3223]

Also, may consider the timing of the future turnaround if the pipe is okay to be skipped the next turnaround.

 

[nd222]

The reduction in thickness is more prominent in the bends with some thinning taking place in straight section also. The design pressure and temp of the line is 5.5 barg and 188 degC respectively.
Thanks all for responding and clarifying.