High temperature buried piping issues

[mch22112]

Hello,

For a 3 mile long 18" carbon steel buried pipeline within a gas processing plant with a max / min operating temperature of 140 / 0 deg C (32 / 284 deg F), what are the major mechanical / stress issues may be encountered? E.g. overstressing due thermal expansion.

Thanks

 

[LittleInch]

Basically yes. 140C is pretty hot and if this is actually cycling from ambient to hot and then back again you'll also have significant fatigue issues and possibly ratcheting of the pipe leading to upheavel buckling. Not to mention what size anchor block you might need if someone decides they don't want some minor movement of the pipework at the inlet and outlet. Much depends on its routing, elevation changes and number of bends / straight lengths, soil type, coating, wall thickness, bend angle and radius. At 140C you also hit de-rating temperatures, not to mention potential to create steam from below ground water unless it's insulated. The operating cycles and usage will be key in this respect.

Depends on the design code how bad it can be and what you can do about it but the pipe, especially after a long straight section (3-400m) will move in the ground at the bends even if you can't see it. You may need to allow for some movement and accept some strain or have to use special backfill to allow movement without creating a void, but some careful analysis and planning is needed. Get it wrong and it will fail in service or come out of the ground, maybe not immeadiately, but in time, especially if numbe rof cycles is higher than anticipated.

Be very careful about any tee connections or small pipes coming off the main pipe as these often cuase real issues and overstress very easily.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[mch22112]

Thanks LittleInch, that's a very helpful reply. I hadn't thought about the issue of steam generation, so that's a good one to flag. We will certainly have to be very careful with the design of this line. Actually, we may be able to avoid 140 deg C via upstream cooling. There is a good argument for this.

 

[LittleInch]

If this is in a plant then it is a prime candidate for surface run piping. Burial will casue you severe problems at that temp, especially if it cycles, but piping designers are much more used to dealing with this sort of issue.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[mch22112]

I agree LittleInch, but unfortunately above ground is not an option for this line.
Cheers

 

[davefitz]

If you can accurately estimate the number of cycles expected over its life, then you might be able to rationalize its UG configuration. The base alternately stress range is proportional to E*a*DT/(1-v) where:
E=young modulus
a= thermal exp coef
DT= 140 C
v= poisson's ratio
Provided butt welds are used for all connections and large stress raisers are deliverately avoided, you can use the design fatigue curves with the known number of cycles and determine the max allowed inherent stress raiser permitted for desing life of the UG system.

Also, as I have seen undulating shell expansion joints used in some types of heat exchanger shells ( 18"), the same undulation style expansion joint can be installed on either side of each of the concrete anchors.

"Nobody expects the Spanish Inquisition! "

 

[BigInch]

Too bad, because neither is below ground an option, if you want anti-corrosion coating. It will break down at that temperature.

Independent events are seldomly independent.

 

[rconner]

While it would obviously increase construction cost is there any advantage for an underground corridor (with pipe supported in same) to as best you can simulate aboveground conditions/freedom underground, if that would help the situation? These sorts of things are now called by some "utilidors", as in some cases more than one utility is supported in/accessed from same etc.

 

[mch22112]

Yes, we will have to do a detailed fatigue analysis. Thanks for the tips Dave. BigInch, there are some new Fusion Bonded Epoxy coating systems on the market that can withstand up to 150 deg C (eg. 3M Skotchkote 135). Rconner, I understand what you mean and it's something for us to consider. However, the cost may be prohibitive as you suggested.
Cheers

 

[BigInch]

Thanks for the tip. I've been working on the opposite end of the temp scale lately. I was thinking that the 130 C temp still held. I wouldn't be ready to use it on a long line, but a 3 miler will be a good test case. Let us know how that works out.


Independent events are seldomly independent.

 

[mch22112]

No problems BigInch, I wasn't aware of them until recently. I made a mistake - I meant Scotchkote 625-155, rather than 135. I will let you know if we go down that path. Hopefully we can avoid 140 deg C via upstream process adjustments.
Cheers

 

[BigInch]

Yes thanks, I saw that. I found the link to the brochure. As we've also had a couple of requests for those temperatures lately, it was interesting to hear that.
3rd reference on page,

http://solutions.3m.com/wps/portal/...9E2FVI20E3000000_nid=TN3VS8ZF8Rbe7C5QZ78847gl

Thanks again.

Independent events are seldomly independent.

 

[racookpe1978]

3 miles underground?

If it goes in at 130 deg, it won't come out at 130 deg C. Or, it will, but will have a lot of condensate. 8<)


Even well insulated in air that would lose a lot of energy, but underground with the insulting can in direct contact to soil/water/rock?

 

[BigInch]

Depends on the flowrate and external temperatures. 200,000 BBLS/day of heavy crude at 170F can travel 125 miles and only lose 40. It arrives at 130F. That's about 1/3 degree loss per mile.

Independent events are seldomly independent.

 

[LittleInch]

It'll come out at about 128 so long as the veleocity is up at about 8 - 10 m,/secthere. There is very little heat loss underground for that distance unless you're in a swamp in which case you've got steam coming out of the ground....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[davefitz]

I just realized the stress issue is not as problematic as orignally thought.

The pipe will be installed at ambient temp 30 C,and may heat up to 130C, inducing a compressive load due to thermal stress. As long as the pipe is provided sufficient "wiggle room", the pipe will horizontally deflect due to compressible collumn collapse, and will relieve the compressible stress in that manner. The same result occurs in boiler loose piping and other cases with long unsupported pipes undergoing cormpessible thermal stresses.

"Nobody expects the Spanish Inquisition! "

 

[MortenA]

These guys are specialists in insuated pipes including HT piping, but i dont know if they operate in the US:

https://www.logstor.com/Brochures/HT Pipes/HT Pipes_EN_P_IN.pdf

Best regards, Morten

 

[LittleInch]

Dave Fitz, the issue is that this is buried pipe. You don't get "wriggle room" when you bury it. It is a serious stress issue which can be overcome, but not easily.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way