Induction Bend Radius for Pipeline with Pigging Requirement

[pplbb2012]

Hi everyone.

This is one simple question but was challenged, hope I can get support herein.

For pipeline induction bend, we usually use 3d (12” above) or 5d (less than 12”) as governing for curvature radius, it actually can facilitate the pigging during erection and operation. I believe such practice must be followed in most engineering design firm.

However, when we review one of pipeline design in which around 2km pipeline are set on jetty and trestle, 1.5d induction bend is provided for the 14” line due to restricted jetty spacing as explained. We were going to advise a higher curvature radius, e.g. 3d, as mandatory comment to be incorporated, unfortunately the stakeholder doesn’t like to revise his design and wonder which code the “3d” curvature radius was specified in.

Honestly speaking, I didn’t find code basis from ASME or API, even in design manual that I own. Can anybody herein guide me for code support? Or was I really wrong that 1.5d can be applied for pipeline with pigging requirement?

Thanks.

 

[brimmer]

There is no code requirement for 3D bends and running ILI tools, it depends on what the operator wants to do. If they want to inspect the line using ILI tools, they will make the bends 3D as you indicate otherwise the line will be difficult to inspect with ILI (at least the conventional ILI tools, the odd tool can negotiate 1.5D on 12" or larger). If there is a "smart" pigging requirement, I would challenge them on how they intend to pass ILI tools. If it is just maintenance pigs, they will pass through 1.5D bends (generally speaking). Have a look at this document NACE Standard RP0102-2002, “Standard Recommended Practice, Inline Inspection of Pipelines”, Appendix A. It gives the 3D guideline with some tools able to make it through 1.5D in larger diameters, though they would have to locate the ILI vendor with this capability/be limited in the tools they can run.

 

[zdas04]

I would push back on using induction bends that tight. Not from an inspection viewpoint, but from a risk of damaging the pipe. If I need 3D or less, I will always use a fitting instead of a hot bend. I've seen 3D hot bends in 12 inch come out looking like an American Football. Tight, big inch induction bends can be done, but the reject rate is very high and by the time you've paid for spoilage, difficult field fits, and time required to exercise the extra care it is way cheaper to buy fittings.

The first ILI tool I ever saw (1991) was limited to 60D bends. That has improved every year since, and 1.5D tools are mainstream today. Anyone who can't do a fabricated (1.5D) fitting can't compete anymore. I don't think that is really a current issue.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[LittleInch]

pplbb,

You have two excellent responses there which I would echo.

1.5D bends are really long radius elbows and not induction bends. You need to make sure they make the ID the same as the pipe in case they use a lower grade material. The only other thing I would say is that you would need to avoid multiple elbows within 3-4m so that the inspection pig ( if this feature is required) does not transverse more than one bend at a time, especially if any second bend is out of plane, i.e. one horizontal 90 followed by a vertical 90.

The key issue is usually risk - the tighter you make the bend the higher the potential for a stuck pig, especially if someone inserts a non flexible or shaft pig.

A pipeline which is mainly or all above ground on a jetty is able to be inspected from the outside so the requirement for internal inspection tools is reduced.

It might be a good idea to use 3D bends where possible as a compromise.

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

 

[pplbb2012]

Thanks Brimmer, Zdas04 and LittleInch, really appreciate for your analysis from different position. I will bring this into review process, 3D bend shall be firmly obeyed.