Process water system surge .. not possible. 8

[jamesbanda]

We are reviewing the hazards of our network for a new project one of our hazard guidewords that is covered in the review is pipework surge.

For process water.. can anyone provide a reference or guidance document covering surge..? Should we consider surge in our network..

if so how its so hugh that is does not seem pratical..?

 

[tkdhwjd]

Liquid filled pipe system can have a surge issue if the flow velocity is high, flowing volume is high, and the flow is suddenly disrupted/stopped (ex. automatic trip valve, etc). FlowMaster is a software that does a detailed surge analysis based on the pipe facilities. I have done draft analyses in the past, but they appeared to be very conservative and only should be used for screening purpose. Unfortunately, I cannot share the method, as it is company proprietary.

 

[MortenA]

James it seems from your post that you are a bit in the woods?

I may be too basic but first I need to understand if you think of the same as me when you say surge and water systems - because there are several definitions of "surge":

- Surge as in waterhammer (would be relevant for a water filled system)
-Surge as in compressor anti-surge - no relevant
- Surge as in a volume of liquid that enters and possibly overfills a vessel
- Power surge (electrical)

More anybody?

The first i mentined may be relevant to your system.

Best regards

Morten

 

[ash9144]

If you are referring to pressure differentials resulting in loss of flow or sudden increases in flow this is not uncommon. Usually water systems feed multiple users. You need to look at the physical piping and run your drops according to individual usages. For instance if you run a tap off of the main header to two users at different elevations with a continuous being higher and a batch being lower then when the batch user takes it will reduce your flow to the higher continuous user.

 

[jamesbanda]

Sorry for not being clear..

Basically for a normal cooling tower circuit.. do you need to ever consider slow closing valves..for surge caused from fast valve closure..


i dont believe you do.., but i am looking to validate this..

 

[bimr]

No, you should not have to evaluate for surge in a cooling tower circuit.

However, large diameter valves should be slow closing to eliminate the potential for surge to occur.

 

[jamesbanda]

Thanks Bimr,

Is your assessment based on an Engineering standard or experience etc..

 

[MortenA]

James

I tend to side with bimr - your dont check for surge in normal water systems.

Best regards

Morten

 

[bimr]

You should reference a piping design manual. Here is an example:

FLUID TRANSIENT ANALYSIS
Loads resulting from fluid transients (such as opening and closing of valves, startup and coast down of pumps) should be considered if they are anticipated occurrences from
normal operation of the system. Fluid transients resulting from Design Basis Accidents should be identified in the project design documents, and analyzed accordingly. Unanticipated transients (transients which do not result from normal operation of the system) need not be analyzed, and should be precluded by proper operating, maintenance and testing procedures.

http://engstandards.lanl.gov/engrman/6mech/pdfs/D20-AppA-ASME_B31.3-r1a.pdf

You should also reference the pressure and temperature of the fluid.

 

[BigInch]

Most all codes require a surge analysis.
Any engineer responsible for hydraulic design or system integrity should do or request his consultant to do this anyway. Its a modern world with modern tools and IMO a surge analysis is not a difficult thing to do these days. At least its required by me, if not by codes.

Any time you have velocities over 5 ft/sec, problems with surge can occur depending on lengths of lines, valve closure speeds, pump power, check valve arrangements, control valve actions, pump starts and trips, etc. Over 10 ft/sec, you will experience at least some minor surge effects and an analysis should be done to confirm that potential problems can be mitigated.

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

 

[bimr]

BigInch states that "Most all codes require a surge analysis."

Would you be kind enough to provide references to locate a few of these codes?

 

[BigInch]

I don't know if its really "most codes" in the entire world, but it is contained within most codes in the developed countries, but that really matters very little. IMO surge analysis today is simply a requirement of doing engineering work to the best of our ability using the latest available knowledge and technology. Isn't that what engineers are supposed to do? In any case, the lawyers know about it, so its better to get it done before things go horribly wrong rather than afterwards.

********************************
ASME B31.3

PROCESS PIPING ASME CODE FOR PRESSURE PIPING

CHAPTER II DESIGN

PAR 301.2 Design Pressure

PAR 301.2.1 (a) The design pressure of each component in a piping system shall be not less than the pressure at the most severe condition of coincident internal or external pressure and temperature (minimum or maximum) expected during service, except as provided in Para. 302.2.4

PAR 301.2.2 (b) Sources of pressure to be considered include ambient influences, pressure oscillations and surges, improper operation, decomposition of unstable fluids, static head, and failure of control devices.

PAR 301.5 Dynamic Effects

PAR 301.5.1 Impact fores caused by external or internal conditions (including changes in flow rate, hydraulic shock, liquid or solid slugging, flashing, and gysering) [/color red]shall be taken into account in the design of piping.

ASME B31.4

PIPELINE TRANSPORTATION SYSTEMS FOR LIQUID HYDROCARBONS AND OTHER LIQUIDS

CHAPTER II DESIGN

PAR 401.2 Pressure

PAR 401.2.2 Internal Design Pressure. The piping component at any point in the piping system shall be designed for an internal design pressure which shall not be less than the maximum steady state operating pressure at the that point, or less than the static head pressure at that point with the line in a static conditiion. The maximum steady state operating pressure shall be the sum of the static head pressure, pressure required to overcome friction losses, and any required back pressure. Credit may be given for hydrostatic external pressure, in the appropriate manner, in modifying the internal design pressure for use in calculations involving the pressure design of piping components (see para. 404.1.3). Pressure rise above maximum steady state operating pressure due to surges and other variations from normal operations is allowed in accordance with para. 402.2.4.

402.2.4 Ratings-Allowance for Variations From Normal Operations. Surge pressures in a liquid pipeline are produced by a change in the velocity of the moving stream that results from shutting down of a pump station or pumping unit, closing of a valve, or blockage of the moving stream.

Surge pressure attenuates (decreases inintensity) as it moves away from its oint of origin.

Surge calculations shall be made, and adequate controls and protective equipment shall be provided, so theat the level of pressure rise due to surges and other variations from normal operations shall not exceed the internal design pressure at any point in the piping system and equipment by more than 10%.

PAR 451 PIPELINE OPERATION AND MAINTENANCE

451.1 Operating Pressure

(a) Care shall be exercised to assure that at any point in the piping system the maximum steady state operating pressure and static head pressure with the line in a static condition do not exceed at that point the internal design pressure and pressure ratings for the components used as specified in para. 402.2.3 and that the level of pressure rise due to surges and other variations from normal operation does not exceed the internal design pressure at any point in the piping system and equipment by more than 10% as specified in para. 402.2.4

DNV-OS-F101 SUBMARINE PIPELINE SYSTEMS

B. System Design Principles

B 100 System integrity

PAR 101 Pipeline systems hsall be designed, constructed and poertated in such a manner that they:

Fulfil the specified transport capacity,

Fulfil the defined safety objective and have the required resistance against loads during planned operational conditions, and

Have sufficient safety margin against accidental loads or unplanned operational conditions.

PAR 254 Operation, Incidental: Conditions which that are not part of normal operation of the equipment or system. In relation to pipeline systems, incidental conditions may lead to incidental pressures, e.g. pressure surges due to sudden closing of valves, or failure of the pressure regulation system and activation of the pressure safety system.

Other International Standards Requiring Surge Analysis

Power Piping ASME B31.1
Process Piping ASME B31.3
Pipeline Transportation Systems for Hydrocarbons and other Liquids ASME B31.4
Refrigeration and Heat Transfer Components ASME B31.5
Building Services Piping ASME B31.9
Slurry Transportation Piping Systems ASME B31.11
Glass-reinforced plastics (GRP) piping ISO 14692-3
Design & Construction of GRP Pipes BS 7159
AWWA Fibreglass Pipe ANSI/AWWA C950
ISO 13623/EN 14161 Petroleum and natural gas industries -Pipeline transportation systems.

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

 

[bimr]

It is true that attorneys parse words.

Reading your code requirements, it is evident that the referenced code requirement is that the piping design takes into account the operating parameters such as pressure, dynamic forces, etc.

However, the code is not requiring a surge analysis. That is something completely different. A hazop study is also something completely different.

It is standard industry practice that cooling water systems do not operate in unusual pressure, flow, temperature, etc. conditions.

So, the answer to the question is that no hazop study is required because the piping design and operating parameters of the system are within piping design standards. The piping person who designed the cooling system should be able to verify that statement.

 

[MortenA]

Biginch

Even though i would love it (more works to me) do you really think that a full simulation would be required by anybody for an open system such as a cooling tower?

Yes i know that there are valves that will close but still i think that not many people analyses such systems.

Best regards

Morten

 

[BigInch]

bimr,

The same code requires stresses to be limited to less than allowables. Is not a stress analysis required?

Reread the red bold text, "pressure oscillations and surges"? Does that not mean transient conditions? Does that not mean surge? Would you explain why that does that not mean do a transient analysis?

What IYO are "Impact fores caused by external or internal conditions (including changes in flow rate, hydraulic shock, liquid or solid slugging, flashing, and gysering)", if it doesn't mean "surge".

I don't mean to suggest that a 2.5 HP pump on a 3" line might require my level of services, but I think its obvious that surge must be accounted for. If just solving the Joukowsky equation works for your system, do it that way then.

I can tell you that no petroleum/PL transport company builds a "real" liquids pipeline without a surge analysis. If you're aware of any that don't, please let me know. I could use the work.

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

 

[MortenA]

We may agree totally - and maybe im spilling hairs - but i was trying to relate to his problem not in general.

A pipeline: Any new pipeline will have such an analysis (I also make them).

Process piping for an air cooler: I think that its quite rare even to check with Joukowsky.

I resently made a transient simulation for a cooling system on an FPSO. But here the problem was that the system could be "dry" and submerged pumps (with boosters) would then fill the pipework - where a CV that normally should maintain the backpressure could cause problems.

Best regards

Morten

 

[BigInch]

A few years ago I did an analysis on a nuclar power plant boiler feed water system. The suction line was quite long distance from an intermediate holding tank and went to a relief vent before arriving at the BFW pump. They called saying that the relief valve was always opening and since the relieved flow was not going to the pump, it went into automatic shutdown. The line was low pressure 128 psig allowable and had a normal low velocity of 3.5 fps. Pump start transients combined with a poorly located discharge check into the high pressure boiler feed was sufficient to cause normal suction line pressures to go over 128 psig and trip the suction line relief valve. Should that be happening on a nuclear power plant? It appears that a surge analysis was done on the suction line, hence the relief valve, but it also appears that somebody didn't do a startup transient analysis.

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

 

[bimr]

A stress analysis is not always required. Refer to the piping design standard referenced above. The piping design standard spells out when you need a stress analysis.

The piping design standard should reference operating conditions such as temperature and velocity. If you stay within operating parameters, then the piping does not have to be analyzed.

 

[BigInch]

Codes don't spell out anything except absolutely mandatory MINIMUM practices. An engineer's judgement for each specific design situation supposedly is better equipped to deal with problematic issues than a code made as a blanket coverall. Codes are engineer's tools, not the other way around.

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

 

[zerosum]

jamesbanda,

We would not do a surge analysis on a cooling tower water system (all ours have open risers) unless there was quite an unusual situation.