×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Process water system surge .. not possible.
8

Process water system surge .. not possible.

Process water system surge .. not possible.

(OP)

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..?
 

RE: Process water system surge .. not possible.

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.

RE: Process water system surge .. not possible.

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

RE: Process water system surge .. not possible.

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.

RE: Process water system surge .. not possible.

(OP)
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..
 

RE: Process water system surge .. not possible.

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.       

RE: Process water system surge .. not possible.

(OP)
Thanks Bimr,

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

RE: Process water system surge .. not possible.

James

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

Best regards

Morten

RE: Process water system surge .. not possible.

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.

RE: Process water system surge .. not possible.

3
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

RE: Process water system surge .. not possible.

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?
 

RE: Process water system surge .. not possible.

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) 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

RE: Process water system surge .. not possible.

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.
 

RE: Process water system surge .. not possible.

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

RE: Process water system surge .. not possible.

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

RE: Process water system surge .. not possible.

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

RE: Process water system surge .. not possible.

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

RE: Process water system surge .. not possible.

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.
 

RE: Process water system surge .. not possible.

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

RE: Process water system surge .. not possible.

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.  

RE: Process water system surge .. not possible.

I've had a lot of stress problems where a stress analysis was not required.  Long pipelines entering stations without adequate flexibility or long pipelines entering stations and making turns with the resulting long pipelines pressure expansion effects (not even at increased temperatures) acting as lever arms on those turns and multiplying by many times the force applied to station pumps and compressor equipment are the most common examples in my CV.  

The real problem with those examples were that they required shutting down the pipeline revenue streams and blowing down products, the costs of which far exceeded the already expensive and difficult required modifications to the pipe geometry, which of course had to be done after the systems were constructed.

I used to take a lotta' crap from my bosses because my projects took more engineering time.  In fact I almost got fired for it, until I doug out all my projects design, construction and what operating-maintenance history they had and presented the VP with solid evidence that increased office engineering time reduced construction field modification work, reduced expensive offshore equipment/personnal standby time, fit together much better and had less modifications after construction and overall costs were only 75 to 80% (not counting modifications afterward, since I didn't have any) of those of engineers running other projects.  Proving that engineering time was the highest overall most cost effective time that we could possibly spend.  Isn't that what engineering time is really all about?  If you can't decrease capital costs, increase system performance, safety and reduce construction and overall project lifecycle costs with engineering time spent, what are we doing here?  

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

RE: Process water system surge .. not possible.

Kudos to Big Inch!! Spoken like a true blue blooded engineer!! I am with you Big Inch 100%
Reena

RE: Process water system surge .. not possible.

Getting back to the point:

Hazop Procedures:

Essentially the Hazops procedure involves taking a full description of a process and systematically questioning every part of it to establish how deviations from the design intent can arise.  Once identified, an assessment is made as to whether such deviations and their consequences can have a negative effect upon the safe and efficient operation of the plant.  If considered necessary, action is then taken to remedy the situation.

This critical analysis is applied in a structured way by the Hazop team, and it relies upon them releasing their imagination in an effort to discover credible causes of deviations.  In practice, many of the causes will be fairly obvious, such as pump failure causing a loss of circulation in the cooling water facility mentioned above.  However, the great advantage of the technique is that it encourages the team to consider other less obvious ways in which a deviation may occur, however unlikely they may seem at first consideration.  In this way the study becomes much more than a mechanistic check-list type of review.  The result is that there is a good chance that potential failures and problems will be identified which had not previously been experienced in the type of plant being studied.

http://www.lihoutech.com/hazop.htm

THe key phrase is  'deviations from the design intent'.

 

RE: Process water system surge .. not possible.

I'm not going to comment on any hazard procedures nor standards for any specific application that say it is not necessary to consider for higher pressures as a result of transient conditions.  I will only say a great many past failures in many applications (of particularly weaker-type piping/joining systems) have been blamed on water hammer or surge (that the systems, since they failed, obviously could not handle).  "Surge .. not possible" are thus quite strong words and should be very carefully considered.

RE: Process water system surge .. not possible.

"Strong words" well said. And quite possibly "last words".

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

RE: Process water system surge .. not possible.

Saying, in the Hazard Review regarding cooling tower water circuit, "Surge - Possible, with excessively fast acting valves.  Safequard - Check the actuation speed of each automatic valve during commissioning and snub air supply if necessary to prevent surge" is not the same level of engineering effort as providing a computer model of transient response for a plant cooling tower water system.   

Obviouly, loss of cooling water to a unit or plant due to pipe rupture has the potential to cause some very serious consequences, so one should proceed prudently. But you have to focus your effort where there are real safety payoffs unless you have unlimited engineering resources.

RE: Process water system surge .. not possible.

One of the most realistic water hammer problems in a cooling circuit is a sticking / slow operating check valve.  It does not matter what the forward flow velocity is.  The reverse flow at the time of check valve closure is the killer.  I was once involved in trip testing  a set of 20" pumps.  i.e. Tripping one pump from a pair running in parallel.  The check valves were brand new and had were specified with defined closing charactistics. The head was not particularly high - I cannot remember the exact head but the pumps were single stage.  I came extremely close to needing a new pair of trousers.

RE: Process water system surge .. not possible.

So would or did computer modeling of the transient characteristics help the situation?

RE: Process water system surge .. not possible.

It can.  Its possible to see any pressure spikes accompanying large transient events.  As 4Pipes says, pump trips, reverse flows from a broken check, slamming check valves, especially when a pump control gets a shutdown signal during a failed ramp up sequence, and control valve malfunction of a fail closed control quite often cause large transients.  Water hammer is basically a function of initial velocity and holding velocities low will avoid many problems, but certain pipe and equipment configurations can worsen the situation when pressure waves occasionally add together at a common point.  The more equipment you have trying to control things seems to increase the potential for trouble.  Transient modeling will help you decide for example, if a thicker walled pipe, or if a surge valve and tank might be the best solution.  Many times you can work out a ramp-up and shutdown sequence to avoid problems completely.  You can also test and determine proper valve actuation times and relief valve settings as well, although just a simple confirmation of maximum pressures reached are less than pipe allowable pressure is often the only objective.

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

RE: Process water system surge .. not possible.


The Joukowsky equation can be used for preliminary estimate of waterhammer or surge.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources