Dear All,

On buried oil and gas pipelines, the anchor block is given. In one of my current projects (a pipeline for gas), I was asked by civil engineer if there was any anchor block in the pipeline. I simply said "NO", as in my opinion (a junior engineer's judgement), for 3" pipeline, it will not be required. Having said all this, now I want to know how we reach at the conclusion that the anchor block is required or not. My guess is that if the buried pipeline is applying too much forces on the plant piping, (sufficient to fail it), we provide anchor block so that all the forces are taken by it and the plant piping can be isolated from the pipeline's effects.

Please enlighten me on this. What are the factors for deciding anchor block (to provide or not to provide)?

Hii,

Its been just a month when I entered in ths field of pipeline.

though I have a little idea about this...but thught of to share with you. The anchor blocks are basically to absorb the displacements being generated in the piepline dut to the presuure / temperature of the fluid within. When the displacements cross the values which leads to the stress limits beyond the allowables, we provide the anchors. In fact, while doing pipeline design, the Anchor force calculations are also been performed.

In addition to this, in case of undergroung to above pipeline transition also we provide the anchor blocks.

Regards,

COS,

Thanks,

But is there really a need to provide anchor block for underground to above ground transitions? What basis?

Shahid,

When the pipe undergoes the said transition, the pipe faces a transition of "Fully Restrained" (i.e, sorrounded by soil) to the "unrestrained" (Open to sorrounding) consition and thus, a large amount of displacements are transfereed to the above ground piping.
This condition arises the need to provide anchor block in the said condition.

Regards,

One of the use of Anchor blocks at transition from UG to AG is to generate an effective boundary for scope change.

At transition from fully restrained to unrestrained piping, an anchor is used to absorb huge displacements n loads (which cannot be restrained by soil alone)and thus stops from transfering them to AG piping designed for flexibility.

If wrong, Please do correct or add to above.

Agreed! But what huge displacements! 50mm, 500mm or 5 meters? I mean at what value we say this is good enough to justify anchor block? What is the criterion for displacement? Also how much loads (sufficient to fail AG piping???)

A displacement of 10 mm alone or axial load as low as 1 ton alone is huge if its causing failure in your AG piping. All depends upon your layout and the amount of flexibility it has.

Sky,

So it is basically the failure of the AG piping which is the criterion!!

so now, if we get a huge displacement and force say 20 mm of displacement and 2 tons of force,then how to calculate the dimension of anchor block it self?
thanks..

You have to contact a specialist in civil engineering for that. It has to do with soil types, ground water levels and a lot of other variables.

see http://www.pipestress.com/papers/UnderGrd-1.pdf. it's a paper where explained this topic very good. greeting

As a guideline, I usually consider the anchor block if the resultant displacement at the A/G U/G transition is greater than 25mm. I picked this up from a stress analysis specification.

Just bear in mind that it doesn't necassarily mean that the allowable stresses for the above ground piping are exceeded if the resultant displacement is greater than 25mm.

Hope that helps

HI
some pipelines widh hight temperaure and pression like gas injection pipeline need to install anchor block in the beginnening and at the end of the pipeline b31.8...but at the transition AG piping B31.4...
my question is , why some pielines like water injection don't need to install 2 anchor blocks , one is enough ???...
please can some one explain me when it's necessary to install the anchors blocks ?
I am begineer in caesar II ....
thanks in advance