direct buried pipe expansion 1

[saliba11]

Do we need an expansion loop or something else for an insulated direct buried underground Carbon Steel piping.

1 meter under tight soil.

Operating temperature is about 100 C.

regards

saliba

 

[BigInch]

Hard to tell you the specific requirements without knowing exactly what the pipe configuration looks like, but at that temperature you will have longitudinal growth and I suspect have a pretty high chance of a buckling failure.

It would be good to know the length, diameter, wall thickness, burial depth, bend locations and operating pressure, etc., if you need any more information about what you should try to do about it.

http://virtualpipeline.spaces.msn.com

 

[dcasto]

Besides expansion, corrosion will be an issue. 100 C is the boiling point of water, at 99 C, freewater can enter the insulation and under insulation is a possibility. The pipe movement will tear up the insulation unless its addressed.

You said tightly packed soil. It doesn't take a computer to say you have a 100% anchored line. The stress is going to jump. In reality, pipe moves underground. I've installed lines in extreme temperatures and we would dig the ditch wider than need by a factor of 4 or 5 times. The pipe would be layed an allowed to bend from trench wall to trench wall knowing that when it cooled as it was buried, it would shorthen up. And vica versa. We had one chemical plant that would not allow us to bury a line because the pipestress program predicted a high stress with a 100 degree F change in temperature. Thats because the program assumes a 100% anchored line. The above ground line moved 14", so an expansion loop (2 of them) were required. Outside the plant area, we went on our way like all pipeliners do, underground.

 

[BigInch]

dcastro, Can't do that any more.

Since the need to transport heavy heated crudes from colder regions with severe environmental temperature ranges has become more and more common, an increase in underground pipeline buckles and consequential environmental damages has made necessary new means of design and installation to prevent overstresses and buckling on underground lines.

From the PBS film about the Alaska Pipeline build in the 70s,

The project also faced criticism from the government's own scientists. They warned that the traditional pipeline construction method -- dig a ditch and bury it -- would not work in Alaska. Prudhoe Bay oil would come out of the ground hot, melting the frozen ground, called permafrost, into mud. The unsupported pipe would eventually buckle, break, and leak oil. The only option was to build more than 400 miles of the pipeline above ground.

However, even 10 years ago, I was making specific design considerations and including them in the construction specifications to prevent overstress and buckling of UNDERGROUND hot (175ºF - 190ºF) lines.

Similar concern for hot line burial stress and buckling has lead to recent work by DNV in an effort to include provisions in their design codes to allow rational design of underground hot lines.

Excerpts from the DNV program,

Uncontrolled pipeline buckling
Similarly, pipelines may be fixed by trenching and burying them below sand or dumping gravel on top of them. This has been the common practice until today.
.............
Due to insufficient measures to mitigate thermal expansion, pipelines are expanding and buckling downwards, upwards and laterally in an uncontrolled fashion, just like a snake moving in random directions.
.............
New knowledge and technology now give us an opportunity to control the expansion of pipelines in locations where this is anticipated. In other words, we can now predict where a pipeline will expand and how it will expand. We can also calculate where gravel dumping and burying is still necessary to keep the pipeline in place.

full text at,

http://www.dnv.com/publications/dnv_forum/by_subject/oil_gas/Bucklinglikeasnake.asp,

Savy pipeline operators have long since been prohibiting the "bury and forget" approach to pipeline design and installation.

http://virtualpipeline.spaces.msn.com

 

[BigInch]

Forgot the PBS reference,

http://www.pbs.org/wgbh/amex/pipeline/filmmore/fd.html

http://virtualpipeline.spaces.msn.com

 

[saliba11]

Carbon Steel pipe is 12 inch and goes straight about 100m without any bend. It is buried 1 m above the ground. At the end of the route it goes belowground and enters into the building.
Operating Pressure is 10 barg.

Does a expansion loop underground prevents buckling failure. If it is so how does a loop works under soil. Can the loop legs have displacements.

thanks in advance

Saliba

 

[BigInch]

If its attached to the walls, it will elongate and fail the wall via punching shear, or more likely buckle, probably to the upward direction. 100 meters length is not sufficient to develop any virtual anchors, so the pipe will tend to slide longitudinally until it does buckle. I would recommend at least one expansion loop, maybe two, placed, in the vacinity of the wall, but not too close to the wall either. Provision for the thermal growth from 100 meters should be allowed in the most unrestricted manner possible. Generally you could place any deformable material inside the trench and along the side of the expansion leg. Wrap the deformable material in a geotextile fabric and then backfill.

If you insulate the pipe, the insulation should be protected with an outer waterproof wrap or sleeve. Be careful what sleevbe material you use. Many materials will get pretty soft, if not melt at that temperature.

http://virtualpipeline.spaces.msn.com

 

[dcasto]

thanks BigInch, next time, get the "r" out of here.

I still wouldn't do anything for a 100 degree F change other than snake it.

My worst case was not a line buckling, it was a side tap. The 3" tap on an 8" line failed. The lines were in the hot sun with no flow as they were welded up and after the being dried. Gas was intoduced and a cold front dropped the temperature and it rain on the lines. The lines contracted and because the 3" was constrained by the ditch wall, it broke (i don't know the mechanics) near the tee and we had a gas release.

 

[BigInch]

r?

Snaking in the ditch is OK as long as the stress is relieved in the process without a local buckle failure, but it gets a bit tough to snake lay a 42" D, so other provisions become necessary, such as limiting the change in vertical and horizontal bend angles under normal cover and increasing burial depth where larger changes in direction become necessary.

http://virtualpipeline.spaces.msn.com

 

[dcasto]

The r in the handle, I do not live in Cuba.

 

[BigInch]

Sorry. Fingers won. I have to fight with my fingers all the time not to put in that r.

http://virtualpipeline.spaces.msn.com

 

[rconner]

dcasto, Unfortunately it appears some multiple subjects, though perhaps with some relation appear running over each other in this thread. I suspect however you are far from being alone in your problem with welded or fused side-connections (see e.g. the poster image illustration on the Battelle failure case study website at

http://www.battelle.org/energy/cases/field.stm).

I also think high coefficients of thermal expansion, recoil effects of some contemporary e.g. potentially high-load trenchless pushing or pulling installations (such as HDD etc.), and also relative settlements etc. of side-connections/services (that even might not necessarily be installed/bedded at the same time) relative to mainlines can further complicate/aggravate this particular problem.

At least early on I know there were some attempts in some areas to make service connections on welded plastic systems e.g. with mechanical saddles and various donut-type rubber seals around the side tap holes. While I suspect pipe breakage such as shown on the Battelle site did not necessarily occur, I did hear that some of these donut seals/saddles eventually ended up slid far down the pipe off the side/tap holes (obviously not doing much good at that point!) Regardless of the method of side-connection, it would appear to minimize the theoretical loads/stresses on the pipe walls that one or more expansion devices and also external anchorage of the pipes etc. relative to same might now be the only theoretical way to totally prevent attempted relative axial movement of the mainline by the station of the side connection. Alas, in practical application even any sort of anchorage will in some fashion put extra loads back onto a welded system pipe wall.

I think it is quite probable that some ability to absorb thermal expansions/contractions in individual mainline piping joints, e.g. with some flexibly joined rubber-gasketed piping systems with low thermal expansion/contraction coefficients, is a particular advantage over more rigid fused or welded systems, particularly when you get to talking about shear and bending effects at side-connections. At this point options in his regard at least for gas piping may be some limited.