Vent and darin for pipelines 4

[brpillai]

Normally high point vents and low point drains are provided for geas venting and liquid darining for hydrostatic testing in pipelines.This is not required after the hydro test unlike in piping within stations, where due to operations requirements, vent and drains are required afterwords also.

In the case of pipelines, containment of the fluid coming out of the vent/ drain is an issue as providing containers/ tanks or venting to atmosphere could cause envronmental issues and loss of product and sometimes even fire hazards.

I am refering to a case of a suggestion to provide a vent / drain point in a liquid sulphur pipeline, to contain the expanded liquid sulphur during remelting ( sulphur expands 10% during re melting) to avoid possible burst of pipeline due to abnormal increase of internal pressure.

Coul any body having similar experience comment on this, whetehr providing vents and darins is an acceptable solution inj this case?

 

[pennpiper]

brpillai,
The location (country) may influence the answer.
Where is this pipeline?

Sometimes its possible to do all the right things and still get bad results

 

[brpillai]

@pennpiper, Thanks for prompt response.

The pipeline is in one of the Middle east ( persian gulf) countries. It laid on the undulating sand dunes.

My concerns ( if this solution is adopted) are that to introduce the vent/ drain, there should be:
Additioanl heating and insulation to make up heat loss.
[ii]Again to collect the spills, containment will be required- may be with heating and insulation.
[iii) I am not able to decide how many locations this facility should be there

 

[LittleInch]

brprillai,

First, your comment "Normally high point vents and low point drains are provided for gas venting and liquid draining for hydrostatic testing in pipelines", Errr, no this is quite unusual. Normally pipelines, not piping, is swept through with one or more pigs (scrapers) with water to remove the air. fitting vents and drains is only valid for some water lines with low velocity.

Liquid sulphur lines need insulation and often trace heating to keep contents at 125 to 150C.

Re heating sulphur from a solid condition is a difficult operation and needs careful monitoring due to the large contraction / expansion and the particular properties of sulphur (very low heat transmission apparently). Vents or any taps would be virtually useless for this sort of product as you would need to pre-determine where the cold spots / solid parts were which could even be within one pipe length. Then you need to deal with liquid sulphur at 125C coming out from any vents. Your vents and drains would need to be heated to this level to avoid blockage.

This sounds like a very early concept issue to me, but you need to know what you're doing with liquid sulphur or you can very easily break the pipeline.

See this report on a sulphur pipeline break in Canada and what they did to avoid it in future.

http://www.neb-one.gc.ca/sftnvrnmnt/sft/pplnrptr/archive/2009spctr-pnrvr/index-eng.html#s4_2_3

My motto: Learn something new every day

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

 

[brpillai]

LittleInch,
Thanks for your very useful commnet. I agree to your point on pigging to remove air from pipelines.
Also to see the report on the incident on the sulphur pipeline failure, and I can foresee the situation.

This particular pipeline, is in laid among sand dunes with undulating terrain. It is difficult to decide the cold spots, though normally anchor supports are the heat sinks due to metal inserts. I understand that providing vents and darins will not be an easy solution, due to requirement of haeting , insulation and selecting the location and providing containment.

After having read the report on the failure (and also heard about incidents at other lcoations)of pipe burst during remelting, I am curious to know whether slower heating near the transition temeprature will be a better soultion to prevent / rule out the possible rupture while remelting.Or is there any other way to prevent the disaster.

I am requesting your valuable opinion, as I understand from your above comment that you are experienced in this field.

Thank you very much once again.

 

[LittleInch]

I'm no expert in heating sulphur lines, but from what I can gather once it starts to solidfy in some places, you actually need to let it solidify for the entire line and let the temperatures stabilise throughout the entire line. This did not occur o the Canadian pipeline and was a cause of a lot of their problems as the heating sections are often not sectioned in small lengths and hence heat the entire pipeline with the same amount.

Good temperature measurement throughout the line (fibre optic cable in contact with the pipe) is required / vital to understand what is going on.

It seems one option is then to rapidly heat the pipe top section near the heating cable to create a continuous channel where pressure can equalise / flow into areas where there are now voids due to the contraction of the sulphur. Once this is established, then slower heating can occur. However it seems there is always possibility of a shock or rapid rise in pressure.

Clearly the best option is not to get to that point and have sufficient reserve power supplies and Nitrogen to completely clear the pipeline inot the downstream plant if the upstream plant stops.

However some sort of plan is very much required for re-heat and at bigger cold spots you might need to provide extra heating.

Some of the trace heating companies seem to have good experience of this - look up Pentair and thermon.

My motto: Learn something new every day

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

 

[brpillai]

Littleinch,
In fact, on a query to Pentair, I got two suggestions
i) to install vents and darins at stretegic locations, with proper insulation
ii) to provide pressure relief valves and gauges at strategic locations.

I am not convinced with both the suggestions, as deciding the startegic location is not easy.There are so many high and low points. Containment is a problem. The line is outside station, as always teh case, not minitoired.

 

[LittleInch]

Fair enough - they are heat tracing specialists not pipeline engineers, but the operation of these lines is limited to a handful of companies and so there may not be much around. I wouldn't go with the drain approach - may they think that if they keep it hot then you can drain it, but that isn't the time you have a problem.

The report from Canada has some good recommendations - I would see if you can find anything more about their procedures if I was you. They got it wrong before so what they have now will be informed by reality and hence should be much better.

My motto: Learn something new every day

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

 

[brpillai]

LittleInch, Thanks for understanding my concern. You rightly said they are not pipeline engineers. They are heating system providers. Let me go though the Canada pipeline report in detail and ponder over it.

I heard that there are about 40+ sulphur pipelines in the world, some of them are operating well, others are having problems when power fails, and insulation issues and eventually leading to rupture of pipeline. In most of the cases, failure occurs at the bends of expansion loops.

 

[LittleInch]

I found these on my travels through the interweb.

http://www.pentairthermal.com/Images/EN-SafeSulfurTransportArticle-WPCS-H58452_tcm432-26452.pdf

and

http://www.pentairthermal.com/Images/GB-SulfurTransportPipelinesEMEA-SB-H58631_tcm432-37911.pdf

where they talk about their "proprietary sulphur re-melt program.."

Maybe you need to speak to the right person....

My motto: Learn something new every day

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

 

[BigInch]

I think it has something to do with heating the pipeline up from the outlet to the inlet using temperature controlled sections. I know someone that worked on the Qatari installation, so I will ask him for more information.

you must get smarter than the software you're using.

 

[BigInch]

"There have been cases where the pipe overpressured when the sulfur expanded, especially where you have lots of 90s. We had a couple of freezes on the skin effect heat traced lines I had in Qatar. We had continuous temperature monitoring by fiber optic cable (1 meter resolution), so we could see exactly where they were. The remelts were handled manually by vendor and usually took several days. They kept turning the heating system on and off until the block was cleared.

you must get smarter than the software you're using.

 

[racookpe1978]

Note the requirement to "drain" that liquid sulfur FROM each entire pipeline section into the low point drain "into something" that will prevent the sulfur spilling into the environment/venting into the air, yet still permit recovery and re-melting of the drained sulfur. Sure, it is tempting to say - "Let it drain into the sand' but that is not viable.

 

[brpillai]

"Let it drain into the sand' so not seem to be a prctical soulution in the view of a pipelien engineer, as the number and locations of the drains can not be decided.

From the above discussions, I understand that the alternative seems to be for incorporating containment of the excessive volume during remelting and allowing to glow to empty spaces ( created during solidification) and controlled heating with close monitoring of the DTS temperature monitoring system.

 

[brpillai]

I understand that Sulphur pipelines are designed as per ASME B 31.4 with temperature correction factor as per 31.8. Is there any other code, used anywhere in placeof 31.4?

I am bringing this point because, 31.4 do not specifically mentioning about liquid sulphur.

 

[LittleInch]

You might want to look at something Like ISO 13623 or even 431.3 as it will give a fairly conservative design for pipelines.

My motto: Learn something new every day

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