Buried Pipeline - Acceptable out of roundness 1

[racp12]

I have to calculate the effects of live loads on a buried pipeline, 26". Among those effects, some ovalisation may occur. My question is: What is the acceptable maximum out of roundness, which will not obstruct cleaning and inspection tool passage?

 

[BigInch]

Non obstruction of spheres, scrapers and instruments is not the issue. Local buckling and weldability is. See what your pipe spec says about it (is it API 5L ?)

http://virtualpipeline.spaces.msn.com

 

[racp12]

Pipe is 26" OD, wall thickness 0.375", API 5L Gr. X-52, code is ASME B31.4, fluid is NGL.
Pipe out of roundness shall be in accordance with tables 7 and 8 of API 5L. Therefore, there is no concern about pipe specification.
My question refers to a situation which may occur as a consequence of live loads applied on the buried pipeline, for instance, a Cat D9 crossing on the terrain surface over the pipeline corridor.

 

[BigInch]

That's not "out of roundness" that's damage.

Depends on which instrument you're running, some can, some can do a little, some can't.

http://virtualpipeline.spaces.msn.com

 

[Zapster]

Without specific ILI guidelines I would start with a look at API 1102, “Steel Pipelines Crossing Railroads and Highways.” Calculate the out of roundness allowed by API 1102. If the calculated out of roundness seems reasonable for cleaning and inspection tool passage, then use that number. If it seems at all questionable, then contact the manufacturers of the ILI tools you plan to use and get their allowable tolerance.

 

[BigInch]

The ovaling allowed by the spec is fine for instrument passage.

http://virtualpipeline.spaces.msn.com

 

[BarryEng]

Your question was directed to internal allowances for, I assume, pigging purposes. There are other reasons to limit 'out of roundness' in a pipe.

The design allowance for 'out of round' depends on several items such as the type of lining & the type of joint.

Cement mortar lining is not as forgiving as a flexible lining. A rubber ring joint is also not as forgiving as a welded joint. The Australian Standard (buried flexible pipelines) - AS 2566, has a limitation on deflection of welded pipe (unlined or flexible lining) of 5%. A welded pipe with cement mortar lining of 3%. A steel pipe with an elastomeric joint of 2%.

Your pipe has a D/t ratio of 60 which is quite stiff for a water pipe. I recently designed a 1,400 mm (11 plate - about the same as your pipe) welded steel pipe (160 m head) with a cover of 750 mm for normal (44 tonne truck) loading. This pipe was on the limit of allowable deflection.

I then checked it out for a 250 tonne haulpak & I then required a 1 m of cement stabilised sand backfill to keep the deflection within limits. Fairly expensive method, but only for a short distance.

One way of doubling the allowable load for a limiting deflection, is to either: -
* Put temporary timber internal struts into the pipe & induce a vertical delection of the max allowable, or
* Inducing excessive compactive effort on the sides of the pipe to induce a vertical deformation.
This means that the surface load will induce a deformation from a +5% to zero, to -5%, effectively doubling the vertical allowable loading. I've never used this method & I only mention it as a theoretical concept. This concept would not apply to your pipe because of the high stiffness.

To answer your original question of a Cat D9 crossing the pipe, the bearing pressure can be quite low under a tracked machine (that is why they use tracks on machines in soft ground - because of their low soil bearing pressures). If you have any concerns of excessive surface loadings, just increase the cover a bit - remember that the surface loading is distributed two ways & dissipates quickly. I use an empirical rule of using 0.5 m of earth loading as being about the same effect as a very large truck.

 

[stanier]

Suggest you download Australian Standard AS 2566.1, including the commentary. This will give you the design procedures necessary for stress, strain, deflection, combined loading and buckling for buried pipelines.

The degree of deflection allowable for allowing the passage of pigs etc comes from the supplier.

The other problem is that when a pipeline is ovalised the flow can be reduced and that wastes energy.

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

http://www.waterhammer.bigblog.com.au