Minimum pipeline wall thickness

[NATIVES]

When a pipe is corroded or dented, frequently a clamp (PLIDCO clamp appears to be popular) is placed around pin hole leak or pipe Thermo warp is placed around the damaged section. Is there any guideline for what should be the minimum wall thickness (after corrosion pr dent) which is considered worth repairing ? What should be the remaining wall thickness in a pipeline which can be considered "beyond repair" and that section must be replaced? Thanks.

 

[RandomAxe]

DNV-RP-F113 provides guidelines on repair of subsea pipelines, also DNV-RP-F107 might be worth a read.

 

[LittleInch]

First obtain true data of the corrosion area and lenght and then you need to undertake an analysis. A curse assessment is often undertaken using ASME B 31G, but also RSTRENG assessment. The amount varies by pipe strength, depth of pit, legnth and width of corrosion pit and design pressure. No assessment goes below 80% of original wt, but that does not mean that is the real minimum as it can be a lot higher if the corrosion area is long and thin or extensive. There are many companies that can do this remaining life extension.

A dent is different and often if the dent is smooth and not less than 95% of the nominal ID, can usually be left in place. The issue is often that the dent is caused by a bucket which has resulted in a gouge as well as a dent. The gouge needs to be ground to eleimate the sharp edge, but all gouges should be clamped and slated for replacement as ther eis significnat work hardening at the root of the gouge which lonk term results in fatigue cracks and also has an effect on wall thickness.

In short, get a proper design assessment of your corroded area.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[brimmer]

As LittleInch suggests, you need to calculate the burst pressure of the feature if it is corrosion, but typically 80% through wall is the cut off. If it is a dent, check your code, but typically you need to repair dents greater than 5% (or 6% in some places). If it is a dent with corrosion in, your code may have guidelines (where I am the corrosion cannot exceed 40% without making a repair). A dent with a stress riser (gouge, crack, etc.) is another matter entirely, you need to look at your repair options - this would be a b-sleeve or compression sleeve if you cannot buff out the stress riser. There are other repair options besides the Plidco clamp, you have to make sure you have the correct repair for the defect.