two pipeline in the same trench 1

[robb4]

Dear all,

I'm involved into design of pipeline system composed by 2 gas pipeline.

I have a small on shore section (500m) and I'm thinking about the possibility to bury both pipeline in the same trench (the route in that section is the same).

Considering that the cathodic protection system is the same for both pipeline (sacrificial anodes, same system used in offshore section) is there any problem / limitation to do that? (such as installation issue, HSE requirements)

Thank for your help.

 

[BigInch]

Bundle them together and install them at the same time.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[rconner]

I admittedly don’t know enough about your specific installation/service to comment much; however, if you decide to somehow yoke your two lines together (for indeed perhaps at least most economical excavation and installation etc.?) you probably should be aware of some behaviors or concerns that might not necessarily exist or be as much visible if single lines were installed some distance apart in separate trenches. Without effective installer etc. provisions to prevent same, these perhaps include the behaviors or concerns:

1. Twin lines fastened together might unexpectedly “rotate” about their axis (for whatever reason, apart from perfect balance etc.) in the process of trying to get them in intended perfectly level orientation the bottom, and maybe in th eworst case rotate even all the way around looking like a corkscrew?
2. Some authorities might have regulations regarding minimum spacings of pipelines for some services, perhaps based on other risks. In this regard some well-meaning authorities and individual Engineers have even gone beyond minimum standards requirements at least for other services, looking at additional issues e.g. regarding potential vulnerabilities re breaks or failures e.g. as talked about in some published papers like

http://scitation.aip.org/getabs/ser...00282040507000046000001&idtype=cvips&gifs=yes

). Large diameter and high pressure critical pipelines obviously might arguably deserve more attention and respect in this regard and many others.

In the absenceof minimum spacing regulations or requirements that prevent yoking the lines very close together I guess any negotiable risks of doing this might be weighed relative to any economic etc. benefits of installing close together etc.

 

[GregLamberson]

robb4

Agree with BigInch. I am currently working on a project where we are bundling 3 ea high pressure gas pipelines (18", 22", and 24") and pulling them offshore through a cofferdam in a single trench.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[StephenA]

Maybe I have misread your question but it seems as if you are talking about a section of landline not an offshore pipe whereas the previous respondents seem to reply based on an offshore pipeline.

Onshore pipelines in a single trench will depend on the Owners requirements for maintenance and risk of failure.

Are both pipelines owned by the same company? This would make it easier to accept.

Stephen Argles
Land & Marine

http://www.landandmarine.com

 

[robb4]

StephenA

The owner is the same for both pipelines.
Another issue for this project is that the work area is swamp one, so we could have some problem during installation.

Anyway according to your reply to investigate the possibility to land both pipelines in the same trench we have to see maintenance program and a quantity risk analysis.

 

[BigInch]

Ah.. this won't be the first bundled lay.... in a swamp.

If you're laying two pipelines at the same time, cost-wise its a no-brainer.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[Rainbowseahorse]

Onshore pipeline, and gas at that, would call for some safety aspect in laying them together in a single trench.

If the land transverse is swampy, as in mangrove/brackish water swamp, then your pipelines will have to be externally concrete coated, and/or even concrete anchor blocks build into the design, for weigh to prevent pipeline from floating.

As for spacing, I think 1 meter spacing would be a requirement for welder work space.

 

[GregLamberson]

Rainbowseahorse:

I would definately stay away from the anchor blocks. As far as the spacing, welder access is not really a consideration in bundling; those sections are welded up separatly at the push site and then "bundled" as they are pushed thru the swamp.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[Rainbowseahorse]

GregLamberson:

Please clarify your reservations on anchor blocks?? Thanks!

Yes, if the pipeline is being installed by push-pull method from a pipeline launching platform into pre-excavated trench filled with water, then spacing for welder would not be an issue.
But if the pipeline is being joined and welded inside trench, as for laying normal land pipeline, then the spacing will become a necessity.

 

[GregLamberson]

Rainbowseahorse

Anchor blocks are not recommended as they tend to impart more stress into pipeline, which requires larger anchor blocks and you go round & round. Basically in a buried pipeline the soil acts as a continuous anchor, the only issues you have are where you come above ground at a facility and in those cases it is always best to manage any movement by design of piping (guides and change in directions) and not with traditional anchor blocks. There have been some good discussions on anchor blocks and stress in previous threads, you can Google "anchor blocks" within EngTips for much more details.

Correct on the spacing. We are currently instaling 3 high pressure gas lines and in areas where it is tight, we are using 1m spacings; for the swamps and shore approach we are bundling all 3; all remaining areas have 10m spacings.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[Rainbowseahorse]

Thanks for your enlightenment on anchor blocks GregLamberson.
I asked that because our Client's consultants have added two anchor blocks each on the swamp & subsea pipeline landfall areas. Guess the consultants are not that experienced afterall!

Can you have a look at my problem in a thread I posted earlier on regarding buckling of subsea water pipeline?
My team of engineers have come up with some interesting proposal, but I would like to see what other experienced engineers have in mind to solve the problem with laying inflexible pipes. Using the "Rintis" method cropped up, but I'm not too crazy with that approach due to the tedious work involved in the many pipeline tie-ins for 27 km long pipeline.

Cheers!

 

[BigInch]

I think the definition of set-on weights and anchor blocks might be getting a little fuzzy. Anchor blocks at landfall areas? Don't know why you would want to do that. Why not let the pipe have a little axial expansion if it wants to. Pipelines with landfalls exposed to currents should be weighted and buried well below the maximum scour depth, but anchor blocks? Do you have equipment there will get damaged if the line expands or contracts too much. What's the reasoning behind anchor blocks there?



**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[Rainbowseahorse]

The pipeline comes straight out of the trench (which is to be backfilled later) and tie-in to the Pig Launcher unit at one end (approx. 12 meters distance), while the other end comes out from the riser, run on pipe supports for 800 meters and tie-in to the Pig Receiver unit.

The Consultant designer specified one anchor block on the Launcher side and three anchor blocks at the Receiver side to prevent pipeline movement.

 

[BigInch]

They're just a piece of pipe. Give the line some flexibility around there. If there's not too much expansion, skid mount the launchers with slots at the anchor bolts to allow the expansion to take place between the skid and the foundation.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[Rainbowseahorse]

BigInch,

Agreed! But I'm sure you've come across Consultants who screwed-up in their design but won't admit to their mistakes to protect their reputation. And the Client, not knowing any better, go along with their Consultant reccommadations.

 

[BigInch]

I've also seen client specs that required anchor blocks every time the pipe had to come up out of the ground too.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[Deepray]

Sorry for the late reply. Just have time to log on and look at the topic. let me share my thoughts.

Anchor block are usually necessary when it come to shore approach as water depth is shallow resulting in huge ENV loads on the pipeline. This will cause in stability to the pipeline. Anchor Block is only one of the method to counter this, others include buried the pipeline, use of high density concrete coating etc.

Anchor block is just a dead weight holding down the pipeline, therefore it come in vary shape and size depending on the designer. The term anchor block used here is different from the anchor block used (one big block casted to anchor restrict and expansion or movement to the onshore side), here Rainbowseahorse refer to a block used to prevent floating of pipeline.

Regarding the spacing the block, it will depend on the design. There is no fast rules on 1m or 10m spacing. Pretty similar to anode design, you can have more spaing if you provide bigger anode at each location. As long as the downward force from the anchor is sufficient to prevent the pipeline from upward or lateral movement.

Hope this helps.

 

[BigInch]

There is no need for an anchor block, perhaps you refer to anchor weighting blocks, still a far less superior choice than coat weighting or deep burial. If its a wave zone where liquifaction is probably more likely to occur than in any other place on the pipeline, anchor weights are the least desireable option.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[chicopee]

In a swamp where there is submerged soil--don't forget about buoyancy problems.