PE pipe and high tempertures

[phllp581]

Hi, I am considering crossing a steam line with a HDPE pipe used to service natural gas. I plan on using a steel casing to help protect from the high tempertures produced by the steam line. Does any one have experience with this or is there any publications that provide guidance on this. I am concerned that the steel casing may not provide enough insulation to protect the HDPE. Is anyone familiar with some calculations to attempt to estimate what the temperture on the HDPE pipe would be in my scenario?

 

[zdas04]

There is nothing that could possibly make this a good idea. Nothing. The strength calcs for HDPE are all done at 72F. Raise that temp to 140F and you halve the MAWP according to the ASME strength calcs. I would say that a 90F strip across a pressurized HDPE line would last several hours before you were dealing with a real problem. Change to steel in the HDPE line about 3 ft either side of the crossing.

The equation you are looking for will not help. You are providing a localized radiant heat source on a very small section of pipe. I've seen HDPE bulge when crossing an 85F gas line and none of the industry equations predicted it.

I don't support using HDPE for natural gas ever, but the non-trival permiation you get I won't sign off on a project HazOP that has natural gas in HDPE inside a structure (like most steam lines are in). This just feels like 85 kinds of a bad idea.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[LittleInch]

What is your scenario - a sketch would help a lot.

Is it buried?, what separation?
What temperature is the "steam" line
Is it lagged / insualted?
What is the outside temp?
Is the gas line constantly flowing?
Relative sizes of lines
Ground type
ground temperature
design and operating pressure of PE line

You've got to do some interesting thermal calcs to show you're not exceeding the required PE surface temperature.

PE is used for Gas distribution on world wide scale, but it has its limits. A section of steel pipe for the short ish crossing length sounds like an excellent idea to me.

Just encasing it in steel sounds like a bad move, especially if you're actually touching one pipe against another, but we can't see what you can see....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[zdas04]

LittleInch,
At least half of the "this system doesn't perform like we designed it" problems that people pay me to address can be traced back to the choice of HDPE for gas lines. It absolutely is used all over the world, but I see an awfully lot of issues that were not anticipated, and wouldn't have been experienced with RTP or steel.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[LittleInch]

zdas04

Really? Was this because they didn't understand that PE is different to steel / comes in different sizes or what?

I would genuinely like to know what the issues are that you come across as I've not seen many beyond the limited temperature/pressure issues, it expands like nothing else, but flow wise - normally does better than similar sized steel pipes.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[zdas04]

The most common compliant goes something like "we budgeted for our wells to make 1 MMSCF/day and we can only get 200 MSCF/day out of them". When I get there I find 800 psi drop across a wellhead choke and ask "why?". The answer is always "to protect the HDPE gathering system." Reservoirs need what they need. Generally a CBM reservoir will need flowing bottomhole pressure to be about half of average reservoir pressure. To get there you have to have facilities adequate for the pressure. Further, since both CBM and Shale have approximately zero native permeability, the flow in the reservoir needs to scour channels to allow a well to meet its potential. In the early days (while reservoir energy is highest) you need to flow the wells as hard as possible to establish robust flow paths that will keep the well flowing economically until you have depleted the gas in place to very low numbers (the CBM field I operated in the San Juan Basin will achieve recovering over 96% of the OGIP). The HDPE makes that impossible. My first postulate is that "every activity, joint of pipe, piece of equipment, and facility should have the goal of maximizing reservoir profitability--any activity which ignores that goal is going to result in sub-optimum performance". Installing HDPE gathering in a new field development ignores this postulate and the huge savings in infrastructure (which never actually materialize, see below) are absolutely a false economy.

The other big issue I see starts with the question "Why is my field development project so far over budget" when they call me in to audit construction methodology. Many of us assume that a steel pipeline project (excluding Engineering and ROW acquisition) will cost about 40% material and 60% labor. I've build or audited over 50 projects that ended up very close to that relationship. I've audited three very large HDPE projects that used that relationship, but HDPE is cheep (and darn well worth it) so the budget is really low. It turns out that buried HDPE tends to have a different ratio--all three of those projects (one in Colorado in the U.S., one in India, and one in Qeensland in Australia) had a relationship of 5% material 95% labor. Also in steel and RTP we never budget hydrostatic retests because they are too rare. Each of these three jobs that I audited (and at least a dozen that I didn't do a formal cost audit on but was working on "how do I get this damn job finished kinds of project") had more than 4 retests and one had 19 retests--all of the failures were at bad welds.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[LittleInch]

Ah, OK. You're talking about field system design and I can see your issue, but it's not really the fault of the poor PE pipe that someone has chosen the wrong material or that the design basis was not correct. You do need a truly integrated project where the requirements of the reservoir engineer are properly understood and then the surface systems designer can make it the most efficient system he or she can.

Weld failures on PE shouldn't be any more than steel if done correctly, but there is sometimes a lack of true understanding about what needs to happen and it is difficult to test joints post welding. Hence that needs to be addressed in the construction sequence to maybe perform more single section tests so that you essentially test as you go and find the poor performing crews before they screw the whole thing, maybe using pneumatic or helium testing.

I didn't think the ratio was 95/5 for PE, but I trust your figures. Interesting.

Each material is different so it all needs a different approach. If you think PE is bad, try GRE - my god that's a hard material to use for a pipeline.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[zdas04]

I live with the single largest accumulation of GRE in the world (upwards of 100,000 miles installed in a single basin). When the tax laws changed to make CBM development attractive, we were terrified (without justification as it turns out) of the CO2 causing steel pipe to dissolve. RTP was still 10 years from being ready for prime time. GRE was the only high pressure, mostly inert option. We have it everywhere and from a "how do I live with it" perspective it sucks a lot. From a reservoir management perspective it is great.

The 95/5 relationship was true on all 3 projects, but I'm reluctant to use it in project economics. Another commonality was that the "expert" doing the welds had been driving a water truck (or selling shoes, or building houses) 2 months before the start of the job. With a company who believes that welding HDPE actually requires skill and training, I would really expect to be closer to 85/15, but I haven't been asked to look at the numbers on any projects like that. Failed welds in the hydrotest was a huge part of the cost overrun.

Material choices that ignore the inherent variability of hydrocarbon production are very common in today's PSM/HazOP/over-Engineering/Under-Thinking world. I've been in 30 HazOP marathons for field development projects where there were zero reservoir engineers or production engineers in attendance. This has been true on 5 continents so I'm pretty sure that it isn't a U.S. thing. In every one of them they write off the reservoir in the first 5 minutes by saying "CBM needs low pressures so we should be shooting for ANSI 150 and HDPE". When I say "what are you going to do when reservoir pressure matches the 1800 psig that the reservoir engineer predicted", the answer is "we'll have an XV and a wellhead choke"

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist