Pressure Surge and MAOP

[Hurricanes]

We have a pipeline and there is a pressure surge due to fast valve closure. A dynamic hydraulic analysis has been done to determine the magnitude of the resulting pressure surge. So far so good. Now, I always though the next step was to take the pressure surge, put it into pipe stress software and determine if the resulting piping stresses were acceptable or not. But the engineer who did the hydraulic analysis is saying the pressure surge is below the MAOP so everything is ok. I don't think this approach is correct, but I am out numbered.

Anyone have any thoughts or references for this situation? Thanks.

 

[LittleInch]

Most pipeline codes allow a transient of design pressure, never mind maop, plus 10%. So your colleague appears to be correct.

You might want to look at fatigue if it happens s lot but straightforward stress it should be fine without doing more analysis.

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[BigInch]

You may be outnumbered, but only one thing for certain is, if max surge pressure is less than 110% MAOP for a ASME B31.4 design, the surge pressure is OK, however there are also limits to the number of times that surges can happen during any given operating year, so investigate that criteria as well. Are you doing B31.4 design?

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[SNORGY]

It's partly the surge, and partly the load on supports that the surge may create, that require evaluation.

Who is right doesn't matter. What is right is all that matters.

 

[Hurricanes]

Its a AS2885 pipeline, so B31.4 applies generally speaking. But in this case it could be argued that it is 'station piping' and B31.3 should be used.

Maybe I am totally on the wrong track, but doesn't the effect of surge on the pipeline depend on the pipe layout? A stiff piping system is going to react differently to a very flexible piping system, is it not?

 

[BigInch]

Do not use B31.3. Not many engineers working with ASME codes outside of the USA really understand that pipeline systems include their pump and compressor stations. Not sure why that isn't obvious, because if you read B31.4 and B31.8, Chapter 1.0, you will find a section titled "SCOPE". There you will clearly see that piping within pump and compressor stations, as well as other facilities within a pipeline system, are INCLUDED. There is no such thing as the infamous B31.3 STATION PIPING "CODE BREAK!"

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[LittleInch]

Hurricanes,

You didn't explain yourself very well in the OP and so I assumed that what you were referring to was a buried, fully restrained pipeline system. What you are now talking about is by the sounds of it an above ground piping system where it is basically unrestrained.

In those instances then yes you are correct. As well as the normal loads and stresses on a piping system ( pressure, temperature, contents weight etc) you also need to look at an accidental or occasional case which involves other forces such as surge loads on elbows, valves and equipment.

Surge per se is not an issue in terms of pure pressure stress / pressure rating of equipement if below MAOP, but can result in excess stress when concentrated in certain locations or if it results in pipes jumping off supports. This you can only really do with a stress analysis program.

My esteemed older brother here (BI) knows I know you can design pump stations etc to B 31.4 and other pipeline codes, but the simple fact is that outside the US it is fairly rare for this to happen and the plant & piping designers feel much more comfortable in designing to B31.3. However YOU have the option to argue it either way you want. There's nothing in the codes that says you MUST do it this way ( the US has legislation that says you MUST design it other pipeline code) so it's up to you to determine which is the most cost effective way.


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Also: If you get a response it's polite to respond to it.

 

[BigInch]

LittleInch. Again, you are thinking only about the pipe. Design of pipe is 100% of B31.3, but only a very minor part of the requirements of B31.4 and 8.

What happens to your B31.3 design when the B31.8 DF is 0.4

Go through both B31.4 & .8 and highlight each paragraph that has a specific requirement for design, fabrication, assembly, erection, examination, inspection and testing of pipeline pipe and other components that has no corresponding requirement at all in the B31.3 code.

Example: Here's one B31.8 requirement that will blow you completely out the client's window.

..... compressor station shall be provided with an emergency shutdown system by means
of which the gas can be blocked out of the station and the station gas piping blown down. Operation of the emergency shutdown system also shall cause the shutdown of all gas compressing equipment and all gasfired equipment. Operation of this system shall deenergize the electrical facilities located in the vicinity of gas headers and in the compressor room, except those
that provide emergency lighting for personnel protection and those that are necessary for protection of equipment. The emergency shutdown system shall be operable from any one of at least two locations outside the gas area of the station, preferably near exit gates in
the station fence, but not more than 500 ft (150 m) from the limits of the stations. Blowdown piping shall extend to a location where the discharge of gas is not likely to.....

B31.3 does not have that requirement. So now what do you do? Catch it on the HAZOP?

Read the scopes. There is no overlap.
B31.3 covers petroleum piping.
B31.3 covers refineries
B31.3 does not cover pipelines
B31.4 covers pipeline systems
B31.4 covers pipeline pipe
B31.4 covers only pipeline piping in pipeline systems
B31.4 covers pipeline pipe onshore and pipeline pipe on offshore platforms
B31.3 covers only petroleum piping in refineries.
B31.3 covers pipe in compressor stations only if compressor station is in refinery or process plant.


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[Hurricanes]

BigInch,

Thanks, for the explanations. Just to be clear, the system is designed to AS2885.1. AS2885.1 splits piping up and defines what is considered part of the pipeline and what is facility or station piping. B31.3 (actually AS4041 is preferred... but software tends not to have Australian codes) and B31.4 are used (with modifications) for pipe stress calculations, not for the complete design, construction, testing etc. So I do not have a choice in many instances with regards to using AS4041 (B31.3).

LittleInch,

Thanks, sorry for not being clear. This is a large above ground section of the system running along a wharf. What you said lines up with what I thought, thanks.

 

[BigInch]

That is so far different from what you said before, "But in this case it could be argued that it is 'station piping' and B31.3 should be used." That's what you said, right.

BUT THERE STILL SEEMS TO BE A PROBLEM! AS 4041 says it doesn't cover gas & liquid petroleum pipelines.
Unless suitably referenced this Standard (AS 4041—1998) is not intended to apply to the following:
(A) Gas and liquid petroleum pipelines covered by AS 2885.

So why are you using AS 4041?

BUT THERE STILL SEEMS TO BE ANOTHER PROBLEM! AS 2885 says...
I'm looking at this older copy of AS 2885

Except for the exclusions listed in Clause 1.2, this Standard (AS 2885) applies to flowlines and gathering pipelines on land and between submarine production facilities. The Standard also applies to pipelines between terminals (see Figures 1.1(A) and 1.1(B)). The extent of the pipelines extends only to where the pipeline is connected to facilities designed according to other Standards. In general, flowlines commence at the wellhead assembly outlet valve on a wellhead, terminate at the inlet valve of the collection manifold, and include piping within facilities integral with the pipeline, such as compressor stations, pump stations, valve stations and metering stations

Although I note further along in the list given that compressors and pump stations on offshore platforms are NOT included, it would seem from the above that compressor and pump stations within onshore pipelines, gathering and flowlines ARE INCLUDED in AS 2885.

So again, why are you using AS 4041?

As I look at Figs 1.1(A) and (B) I see only confirmations of my observations above.

It would seem to me that AS 2885 is the only code that applies to your system and that if you have pump stations, or compressor stations in your system, they too will be included in AS 2885, unless and only if your compressor or pump station is on an offshore platform.
Can you explain why you think it does not and why you think you need both 4041 and 2885?

Now that we all know what codes you are using, tell us the answer to your original question. you will find the answer in those codes. What is the surge pressure allowable for AS2885.1 and for AS4041.

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[Hurricanes]

Hi BigInch,

Why am I looking at AS 4041? Because AS 2885.0-2008 Figure 1.1 and AS 2885.1-2012 Figure 4.1 are quite a bit different than those 1997 figures. Figure 4.1 shows the break between pipeline and station piping. And then, section 6.1 of AS 2885.1: Design of station pipework shall comply with AS 4041 or ASME B31.3, except as provided in Clauses 3.2 and 3.4.3....

Also, the part of the scope section you quote from 1997 has been deleted from the 2012 version of the standard. Compressor and pump stations within onshore pipelines, gathering and flowlines are included in AS 2885 from a governance standpoint, but not design.

Regardless I do not think this addresses my original question. If you have hammer in an above ground system, the magnitude of the surge pressure is not going to tell you what the stresses are in the piping unless you do a dynamic analysis (right?). Section 3.10.3 of AS 4041 gives the allowable pressure variations above design, but those do not account for dynamic effects, rather they are more for short periods where the pressure or temperature in the pipe rises above the design value.

 

[BigInch]

OK. Thanks. I saw that it was an old edition and thought things might have changed since then. So if you're not using B31.4, I'm happy with that explanation.

Dynamic stresses.
ASME B31.4 allows 10% over design pressure as the maximum permitted transient pressure. B31.8 (gas pipelines) does not allow any increase of transient pressure over design pressure. Stress increases during transients are just considered as linear. 10% higher stresses at the max allowed transient pressure of 110% design pressure. In B31.4, the allowable pipe stress safety factors cover these dynamic effects. Unless you think that the dynamic effects might be extreme for some reason (high pressure, steam driven, pipe whip effects for a pipe break in a nuclear plant, etc.) that the codes did not consider, that is usually the end of the transient analysis.

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[LittleInch]

The piping engineers I coma across tend to get very excited about surge forces on piping systems, though I don't know what generates the forces for them, but the loads on the bends can add up to quite a large amount relative to a piping system.

Buried lines the dynamic forces are relatively small and can be ignored most of the time, but piing is much more susceptible to relatively small loads at key locations.



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