B31.3 vs B31.4 Stress Analysis

[MickMc]

Hi,

In a developing project our senior management have taken decision not stipulate interconnecting pipelines between process units to be piggable and as a result of this we are considering no code break between ISBL and OSBL and all will be to ASME B31.3. We will be considering temporary pigging for commissioning purposes and possibly future cleaning and will have barred tee/full bore valve/provision for kicking line and pig trap envelope reserved inside each battery limit.

Our basis is that we have relatively low pressure in Class 150 piping therefore wall thickness will be Standard schedule for mechanical strength which is in excess for calculated under B31.3 & B31.4 and there is no requirement for PWHT by code or service (gasoline)and no requirement for induction bends. Interconnecting pipelines (7km & 6km) will be in existing pipe corridors and aboveground except at road crossing in duct banks and also in some cases overhead bridge crossing at intersecting corridors.

Are there therefore any advantages, economical or not, to using B31.4 for the interconnecting pipelines in this case and I was thinking if any may they be in stress analysis where I believe different yield strengths are used e.g. would it reduce number of expansion loops etc?

Regards.

Mick.

 

[BigInch]

In the USA whether a pipe is a pipeline or a pipe is not a management decision. With the road crossing and RoW, if not the owner's property, this could be a pipeline. Outside the USA, where you may not be so rigidly bound by CFRs and codes have some "flexibility", you can pretty much call it whatever suits your convenience, as long as the owner agrees.

B31.8 is slightly more conservative than B31.3 in 0.50 Design Factor locations. B31.4 may have a very slight advantage to wall thickness, but nothing that is likely to help you for such short pipelines. You will undoubtedly have to choose the next higher standard wall thickness and therefore highly likely to lose any presumed advantage, not to mention put you at odds with management. My advice outside the USA, let it go.

 

[MickMc]

BigInch, Thanks for prompt reply.

We are in fact outside USA in Middle East and I am working on owner/client side therefore stipulating to future contractor which code to use which would be B31.3 or B31.4 as they are liquid pipeline. My only concern is that there may be some advantages in using B31.4 that I am unaware of not related to wall thickness, we will be choosing higher standard than calculated in either code, as my exposure to this code is limited as my experience is normally B31.3.

It would be no problem putting code break at barred tee location inside battery limit but if no real advantage preference would be to use the one code B31.3 which we have to use inside process units.

Regards.

Mick.

 

[BigInch]

In general you shouldn't put in unnecessary code breaks. It complicates testing, retesting, valve and material purchasing (valves must be API6D, etc.), it may influence control type and selection, future record keeping. It can have an a knock on effect much greater than it initially appears that lasts for the lifetime of the plant.

 

[LittleInch]

Yes it might complicate testing a little, but if you've got 6 to 7km of line outside of a fenceline then it would normally be best to call it a pipeline if this is not a mandated issues. The key issue here for me is that this is essence a very long above ground pipe rack and hence 31.3 is probably better suited than 31.4 which is much better when buried.

If you're going to pig it for commissioning and cleaning then you need bigger bends really.

Not a easy one to call from a distance. I would probably go for 31.3, but use 3D bends... even if you only really need to pig it once or twice in its life to commission or repair / clean / inspect, then it will be worth it. For 6-7km, everything else is very marginal, especially for unrestrained lines above ground.

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

 

[pennpiper]

MickMc,
You wrote:
(1) "In a developing project our senior management have taken decision not stipulate interconnecting pipelines between process units to be piggable"
Here you have used the one word term "pipelines". To me and many others this commonly refers to off property , cross country transportation of fluids or gases. The two word term "pipe line" related to all the various pipe systems inside the fence/property of a Refinery, Chemical Plant, etc. Please clarify, using these concepts are you talking about a pipeline or a pipe line?

(2) "and as a result of this we are considering no code break between ISBL and OSBL and all will be to ASME B31.3."
In my book OSBL and ISBL are both inside the fence/ property line therefore they would both be ASME B31.3 except when the cross country pipeline Care, Custody and Control (CCC) extends inside the fence for some special reason. All piping in an Interconnecting Pipe Rack would be pipe lines therefore B31.3 and would not be designed for pigging.

(3) "We will be considering temporary pigging for commissioning purposes and possibly future cleaning and will have barred tee/full bore valve/provision for kicking line and pig trap envelope reserved inside each battery limit."
Battery Limit is the designation for a Unit or Area Boundary inside a Refinery complex. I am having a real problem trying to visualize how you are going to accomplish "temporary pigging" for all or even a few of the pipe lines "inside each battery limit".

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

 

[MickMc]

Pennpiper,

I do see where I may be confusing people therefore to clarify.

1. The 'complex' is an industrial hub circa 17 square mile containing within its limits various process plants including GTL, LNG, Gas Processing & Refineries which in this context the pipelines I am referring to are interconnecting these plants whether to tank farms, jetties or each other in above ground sleepers in pre-designated Pipeline Corridors (owners definition).

2. The areas inside the plant fences are termed ISBL and outside plant fences OSBL by owner and as mentioned all pipes OSBL are termed pipelines by ownner and for clarification I would term ISBL as Piping and OSBL as Pipeline.

3. Temporary pigging will only be for the interconnecting Pipelines as termed previously with barred tee etc in optimum location inside plant fence swith space envelope reserved for temporary launcher/receiver as and when required. We will have a Process & Utility Plant with its various battery limits between units but pipeline segments will be to Tankage area, Jetty and Tanker Loading all circa 7kms between each other.

Hope this clarifies somewhat.

Regards.

Mick.

 

[pennpiper]

MickMc,
Okay I think I got it now.

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

 

[BigInch]

1. The 'complex' is an industrial hub circa 17 square mile containing within its limits various process plants (not B31.4 or 8) including GTL, LNG (not B31.4 or 8) , Gas Processing & Refineries (not B31.4 or 8) which in this context the pipelines (not B31.4 or 8) I am referring to are interconnecting these plants whether to tank farms (not B31.4 or 8, unless they are "breakout tanks", they are not) , jetties (not B31.4 or 8) or each other in above ground sleepers in pre-designated Pipeline Corridors (owners definition).

They may be pipelines, but they are not B31.4 or 8 pipelines.

 

[MickMc]

BigInch,

There are a mixture of 'Pipelines' in these corridors which are either coming from wellhead platforms, interconnecting plants or exporting from plants. The wellhead pipelines do as far as I am aware have permanent pigging facilities and would be to appropriate code whether liquid or gas (buried) with the interconnecting pipelines more a grey area and seemingly more project driven with no instruction from owner. The various plants within the complex are operated on behalf of owner by different OPCOs' with OSBL managed by a single entity consisting of essentially the pipeline/power/utility/telecom corridors and general infrastructure. The end user (Plants) will propose a pipeline route under provided guidelines along with appropriate drawing and documentation to this entity for final approval.

I am not privy to the code details of existing interconnecting pipelines except for one similar recent project which is in operation and has elected to use B31.4 for pipeline corridors but would say on site visit except for this project the other pipelines I witnessed do not have induction bends.

I think we have digressed a little from intent of my original question which was to get a feeling if there was any real advantage to using both codes and feedback from yourself and LittleInch have confirmed my own preference for using the one code and we will consider 3D bends.

Thanks everyone for your valuable input.

Regards.

Mick.

ps. I have just joined project in recent months and have not worked for this client before therefore a bit hazy on history of the complex.

 

[BigInch]

Right. I was only trying to reassure you that there is no overpowering reason I see to switch to a pipeline code there. They can all be B31.3 "Pipelines".