Cross-Country Steam Pipelines - Design Code to Use?

[acedude]

I would seek recommendations on which International design code to use for a 20", 6 Km, HPHT (900#, 600 degree F) cross-country steam pipline. My problem is B31.1 and B31.3 do not allow higher grade API 5L line pipe at these temperatures, and A106 Gr. B results in very high wall thicknesses. B31.8 allows use of API 5L higher grade line pipe (X60, X65 etc.) only up to 450 F. Any suggestions?

Also, does anyone know of any insulation that has proven long term performance against moiture degradation which would allow consideration of burial for such pipeline?

 

[athomas236]

I know nothing about cross country steam lines but tactfully suggest that if 4 piping codes do not permit the use of API 5L at the conditions you want, maybe it is not suitable.

athomas236

 

[Ashereng]

I am curious as to why you are sending steam 6 km across the country?


"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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[dcv]

The Canadian Pipeline Code CSA Z662 has within it, Section 14, which deals with above ground cross country steam distribution pipelines. The section largely defaults to B31.3 design with higher grades of pipeline material allowed.

 

[KevinNZ]

Cross country steam lines are used for geothermal power stations. typically the design pressure is no more than 30 bar. Wellheads can be up to 100 bar. But I know one porject design a pipeline for hot water at 250 bar and 215C.

We use B31.1.

I have not seen any codes that allow higher stresses for the X grade pipe at high temperatures. You only get higher design stresses at low temperatures.

Line are not buried as we have to allow for thermal exspansion.

Just completed a 3km 60" line.

 

[acedude]

All Respondees,

Thanks guys, this has been helpfull. The particular application for this steam line(s) are reinjection for enhanced recovery, therefore the reason for the high pressures. One of the other problems being the steam source is located 6 km from the field. I will look into the Canadian code, I did see this referenced in a persons CV for steam lines when I was searching the web last week.

I agree that the thermally induced stresses for a buried restrained mode would dictate an increased wall thickness beyond that required for pressure alone at these operating temperatures, and the thrust load at below ground/above ground transitions would be huge, and the line could emrge from the ground if insufficient cover is not provided (i.e. deeper burial.

However, the above ground construction mode costs are also significant to permit the large discplacements with the necessay anchors between loops, and the loops themselves would be significant....unfortunatley, such are the limited choices for HPHT lines.

I am new to this forum, and I think it is great...thanks again.

 

[TBP]

There really isn't any way around providing an expansion allowance for steam lines. Buried district steam heating systems in urban areas, military bases, college campuses, etc use expansion joints. There's no money to be saved by burying the line, and installing expansion joints, plus, the joints are maintenance items. I've worked with a lot of steam systems, some buried, some above grade. Trust me, if you possibly can, put the line above grade, with expansion loops. Cheaper to install, and FAR easier to inspect/maintain.

 

[dcv]

The Canadian CSA Z662 code Steam pipeline section was developed for sending steam to injection wells for secondary revocery too. Expansion loop layout is a big part of the design. Typically allow for about a meter of pipe movement from each side into the loop, and the legs of the loops are at 45 deg, not 90 deg, to the mainline.

Dave C

 

[BigInch]

Considering the insulation that soil cover could provide, I would think burying a steam line in Canada might pay for itself pretty quickly with the savings from lesser thermal losses. But this 600ºF heavy wall thickness pipe will be nearly (if not totally) impossible to restrain, buried or otherwise. It is possible that burying it sufficiently deep to keep it from buckling up and out of the soil at overbends and horizontal bends, will overstress it, even if the resulting axial thermal load is compressive. It may also be necessary to limit the degree of both horizontal and vertical bends to reduce excessive eccentrically caused moment, resulting bend stress and vertical and lateral-and-up movements, and thereby also reduce required burial depth. That bend limit will very likely be quite small. Any point where absolute anchoring is needed will require a tremendous amount of concrete unless an equal amount of flexibility is allowed on the free side.

Another problem you may have is coating the line for corrosion resistance. UG pipelines typically use a FBE corrosion coating with a 1 or 2 layer PE mechanical protective coating on top, but any PE layer will not withstand 600F. FBE is too thin to bury without providing some mechanical protection.

If burying is feasible, it might be good to allow for smart pig inspection (provide launchers and receivers), if not required by the CA code. For that matter, it may also be desireable (or required) for AG.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[TBP]

If the line is left in service & hot for most of the time, external corrosion won't typically be an issue. The carrier pipe almost always stands up very well, unless it's shut down for extended periods, such as building heating lines shut down for the summers. (Welcome to "corrosion central" - the line will corrode from the outside-in, often at an astonishing rate.) The big problem with buried steam lines is the insulation & jacket. In many installations, the field joints on the insulation jacket routinely fail after a few years. Moisture gets in, and steams-off from the heat of the carrier pipe, shredding the insulation. The heat loss from the line skyrockets, sometimes overwhelming the capability of the drip traps to handle the resulting condensate, especially on a start-up after outages like maintenance shutdowns. This can result in some "interesting" water hammer events. (Ask me how I know this...) Wayne Kirsner has a great website on this subject -

http://www.kirsner.org

In my exerience, bury steam lines only if there's no alternative. Much of what people know about above grade steam line installations in buildings, plants, etc simply doesn't translate very well to the underground stuff.