B31.4 Existing Pipe is Overstressed -what's the path forward?

[PaperEngr]

Hello everyone, a bit of a general question:

Let's say there's an existing above ground pipeline with one small section to be modified. Upon review there is concern that it currently does not meet B31.4 Code, occasional stresses are too high, inadequate supporting, etc. But it's been there 30-40 years in operation, no issues. If there are modifications done, does the entire line then need to be made to comply with the Code? This line has practically zero restraints, so there's not an obvious point to end the calculation.

Line is 16"NPS, A106-B, Std Wall, hoop stress below 20% yield.

Thanks in advance!

 

[LittleInch]

Not enough information to make a comment.

B31.4 is not the best code for above ground systems and all code will be conservative as will any analysis. Reality is different.

Looks very low stress for pressure so lots available for thermal.

 

[akpipelineengr]

What is "required" depends entirely on the owner's requirements and any applicable regulations. In general, you don't have to go back and bring the line up to meet current code requirements, but you do need to determine if any of the issues you have identified are fitness for service issues.

Pipelines in operation often no longer meet the original design code for many reasons (e.g., corrosion) but can still be fit for service. It's hard to comment on your situation without more detail.

 

[LittleInch]

How far you need to model is not fixed. If no clear anchor or line stop then I would go at least 200m from your modification.

Might be a bit excessive, but when you make changes, you get blamed for anything happening even if the fault or overstress is already there.

So model it now in its as Installed condition and don't make anything worse with your changes.