Anchor Block. 4

[Frank1344]

Hello Folks,

I was asked if there is any alternative to Concrete Anchor Block we use in a typical pipeline systems.

I heard about using Etha Foam, but not quite sure how it works.

Any idea, guides, tips, hints on this is greatly appreciated.

Frank,
Calgary, Alberta

 

[BigInch]

Anchor block at the station gate?

I don't use them unless the client demands one. Anchor blocks are somewhat self-defeating. The bigger you make them, the more force you have to anchor with them.

The only alternative to anchor blocks is to provide flexibility and accomodate the movement. I find that a short segment of axially guided pipe, followed by as long a straight run out of the station as you can make, followed by a 90º turn into the pipeline right-of-way works best. If the straight run from the station can be made long enough, you may not need any anchor blocks at all. The guides should be (but not too) near any equipment. That 90º configuration usually works, since it just happens to be convenient to put booster stations along the side of a passing pipeline's RoW.

A foam filled trench will allow movement, but is not of any real help, since you must still assure that the PL movement does not act as a lever (pinion near station fence) and try to slide equipment, compressors or pumps inside the stationm in the opposite direction, in the case of the 90º configuration, or just ram into the station and equipment, in the case of no 90 bend.

http://virtualpipeline.spaces.msn.com

 

[dcasto]

I've always been against anchor blocks but could not express it as well.

 

[Frank1344]

Thanks for the feedbacks.

I am not a Pipeline expert but I saw on most of the designs there is a an anchor block right before the pipeline coming off the ground and I got the impression that this is a design practice designing a pipeline but apparently I am missing the concept of using anchors on the pipeline system.

Would you be able to elaborate more on this subject?

With Respect,
Frank

 

[BigInch]

Yes I can. They're very common at the last underground point available, mostly 'cause they usually require a really big hole to put them in. Its a typical result for a preliminary type conceptual design and/or for a pipeline that has not had a proper end stress run, or done "yet".

My whole theory with pipe stress and flexibility is, if possible handle the movement by allowing for it intelligently, since every anchor you place in a piping system causes stress which must be anchored, which ususally causes more stress... That's a recursive function, so its much better to control the growth in acceptable directions and use as few a number of guides and anchors as possible.

There's a lot of oil companies (SaudiAramco, Conoco... )that simply require them because some refinery rotating equipment engineer doesn't want to take any chance that any movement of a pipeline will misalign some compressor or otherwise disturb his day. It is a valid concern, but not for blindly requiring large anchor blocks. S.A. requires pipeline anchor blocks and that they NOT move at all. Yes, Zero movement, which is theoretically impossible since you always have to rely on mobilization of at least a tiny bit of lateral active soil pressure to get them down to a reasonable size. Otherwise overturning moments are very large which translates to a very large footing or base size. Nontheless, they were required, so I designed and built them. Fortunately I was able to get them to allow calculations showing 1/2 inch of movement.

With pipelines, there is usually enough room before arriving at the plant to allow for a lot of movement. I've even used slotted connections on sphere launcher skids to allow the pipeline to move the launcher and skid back a couple of inches. That, combined with a 90 and a nice run of perpendicular "expansion leg" piping into the station, supported on sleepers where the pipeline on top can slide horizontaly on bearing plates (with slotted bolt holes to avoid lever actions) welded to sleeves which are clamped on the pipeline works very nicely. I've had more misaligned compressor problems where I found that the misalignment was caused by a poorly placed anchor block than I've had on systems without anchor blocks and my first respose in such a situation is to get a cutting torch and start burning off anchor attachments... except for one guide in the right place.

Usually you will not have to design for more growth than you will get in a maximum of 1500 feet of pipeline. Soil cohesive and friction forces generally will add up to be enough to hold a typical pipeline by the time you have buried about 1000 feet in most cases (by forming a "virtual soil anchor"), so unless its a very hot line or something, pipeline end movements are usually limited to a couple of inches at most.

IMO, most of the time for pipelines anyway they are pretty useless, and typically actually cause more stress and force to be transmitted into the station, since they are often just built at the fence without any stress runs from there into the station ever having been made. The usual response is "we stopped the movement, nothing to worry about now. So why do we need a stress run?" ... go figure.

http://virtualpipeline.spaces.msn.com

 

[Frank1344]

Thank you.

 

[dcasto]

My experience is kinda the same. The big pipeline companies need to use up engieerstime when not building and they needed documented design things so the set up internal standards for all kinds of things, like anchor blocks. There may have been a need based on some early pipe coming out of the mills in the mid 40's early 50's when most pielines were being built. Pipe would rupture near compressors. There were also problems with welds failing (Liberty Ships). Today the steel is better, the welding better and the need for blocks has subsided.

I had a young engineer that was putting in a flare header and because we were on another plant property he needed a pipe stress study. He had it run and his whole flare pipe system was in excess stress. I took one look at the input iso and all he had was anchors at every cornor it turned going through the meter yard. I told him to remove at least 2/3 of th clamps and all but one section freed up. I wanted to bury the line, but the plant owner said we couldn't because the earth is an anchor. So we went above ground and when we put an overhead bridge for vehicles, that u shape gave us our spring we needed.

 

[GregLamberson]

I'll chime in with agreement. As BigInch pointed out, if you have a hot oil line, it is important to look at the effect of temp differentials and the combination of stresses (tensile, hoop compressive longitudinal).

Look at Sect 419 of B31.4 deals which with expansion and flexibility (assuming that's your governing code). It will give you the equation for calculating the net longitudinal compressive stress due to the combination of internal pressure and temperature rise (sect 419.6.4(b)). The allowable value for equivalent tensile stress is limited to 90% of SMYS (sect 402.3.2(c)).

As far as why at pig traps - this is where the pipeline changes conditions from fully restrained to unrestrained, and where, as BigInch points out, the majority of your deflections and stresses are found. This is the point where you want to find out what the longitudinal stresses and deflections due to intwrnal press and temp change are. In addition to being in the best interests of your pipeline, it is in your economic best interests to design in enough flexibility to accommodate the deflections and "naturally" constrain movements.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[MJCronin]

Frank,

"BigInch" has led this thread into a discussion of anchor blocks versus flexibility anaysis......but I am not sure that that was your original question.

You asked: "...is any alternative to Concrete Anchor Block we use in a typical pipeline systems ? "

Are you asking about buried piping systems that typically use a "bell and spigot" construction ? Are you asking about the use of anchor blocks to restrain the affects of PRESSURE in the system, not THERMAL EXPANSION ?

If so, then this whole thread has gone in the wrong direction and there are products and systems commercially available that might help....

My opinion only....

-MJC

 

[BigInch]

I would call "none" a cost effective alternative, but you're right, it was not the original question. What are the other alternatives?

http://virtualpipeline.spaces.msn.com

 

[GregLamberson]

Screw anchors.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[Frank1344]

OK,

Very good point.

The assumption is that there is an anchor block requirement to be used either by Client or stress analysis calls.

Now, is there any other ways of anchoring the pipe without using concrete block, anchor flange,....

One friend of mine told me he has seen using EthaFoam 220 by DOW installed on the S bend before coming off the ground but he is not able to explain more on this.

My question is, is there any body who was exposed to such a thing? If yes, how it works?

One more thing, the size renge I am talking is from 4" to 8" maximum.

I hope it helps clarifying what I am looking for.

At the same time I highly appreciate all the inputs from you guys. those are very valuable to me.
Frank,
Calgary

 

[GregLamberson]

Frank1344

You may want to look at pipeline screw anchors. I have used them in lieu of concrete weight coating or weights for bouyancy control, never for longitudinal deflections, but you never know.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[BigInch]

Greg, as you said, screw anchors are really only for vertical stability control. They can only be loaded axially (presumed vertically), as they don't have shear resistance for a perpendicular axial load.

I have used foam, but to permit unrestrained movement by the pipe into the foam. Without foam the pipe would presumedly ram the backfill into laterally and up against the trench edge then out of the ditch. Since foam allows movement, I would not say it could "technically" be considered an alternative for an "anchor", which stops movement.

http://virtualpipeline.spaces.msn.com

 

[yobaykal]

BigInch,

You wrote "I find that a short segment of axially guided pipe, followed by as long a straight run out of the station as you can make, followed by a 90º turn into the pipeline right-of-way works best. If the straight run from the station can be made long enough, you may not need any anchor blocks at all. The guides should be (but not too) near any equipment. That 90º configuration usually works, since it just happens to be convenient to put booster stations along the side of a passing pipeline's RoW." Could you please explain this more if possible with a simple sketch?

 

[BigInch]

Nothing complicated. I was thinking about something like this. Foam or a covered "utility" trench can provide freedom for pipe movement in cases where movement is predicted to be excessive.

http://virtualpipeline.spaces.msn.com

 

[yobaykal]

thanks.