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NPSH margin and ANSI/HI 9.6.1
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Source：Internet Author：Unknow Pubdate：2008-12-11
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athomas236 (Mechanical)
9 Dec 08 11:26
Gentlemen,
I have been asked to investigate what NPSH margin should be applied to power plant boiler feed pumps.
I have discovered that ANSI/HI 9.6.1 addressed this particular matter. However, although this standard was re-confirmed in 2000, it appears that it was withdrawn in 2003.
As far as I can tell this is the only standard that has addressed the issue of NPSH margins and I want to use the limits within this standard. But before doing so, I want to understand why it was withdrawn.
If anyone can explain why it was withdrawn or advise of any other applicable standard I would be grateful.
Best regards,
athomas236
Artisi (Mechanical)
9 Dec 08 14:57
Seems logical to ask the Hydraulic Institute why they withdrew it.
字串1
athomas236 (Mechanical)
10 Dec 08 5:00
Artisi,
I agree with you and have emailed the Hydraulic Institute accordingly, awaiting a response.
I am trying to obtain a copy of standard ANSI/HI 9.6.1 even though it has been withdrawn.
I am also trying to obtain a copy of ANSI/HI 1.3 just in case it offers advise on NPSH margins. Looking at the contents list, I am not hopeful that this matter will be covered in the same detail as in ANSI/HI 9.6.1.
At the moment I understand that the sales of this standard ANSI/HI 1.3 have been suspended because of errors in the formulae in the standard.
The reason for posting my original question was to obtain advice from engineeers working in the pump field and I would still welcome any response to my original post.
Best Regards,
athomas236
Artisi (Mechanical)
10 Dec 08 6:08
字串9
It will be interesting to know why this was withdrawn but anyway the NPSH margins seem to be acceptable for many people and manufacturers.
However, if you are talking about high flow / high head BFP's I would certainly opt for the higher figure that was in 9.6.1., of course there may well be others with actual field experience for the same equipment you are considering in similar installations and this could be your guide to establishing margins. A check with manufactureres and or users would be well worth while if you do not get any good response here.
athomas236 (Mechanical)
10 Dec 08 7:43
Artisi,
Thank you for that information. I have ordered 9.6.1 today and found that someone in our Dubai office has a copy of 1.3.
If I get a reply from HI, I will let you know.
Best regards,
athomas236
athomas236 (Mechanical)
10 Dec 08 8:38
字串2
Artisi,
Shown below is the complete response from HI.
Best Regards,
athomas236
QUOTE
Dear Mr. Thomas,
Thank you for contacting the Hydraulic Institute (HI) and for your inquiry regarding the NPSH Margin Standard, ANSI/HI 9.6.1 (1998).
This standard was approved and published in 1998 and has been distributed to a wide readership. You may be aware that ANSI requires that all standards be reviewed within a 5-year period and reaffirmed, updated, or withdrawn. In keeping with ANSI requirements, a review committee was convened in May 2002 for the purpose of reviewing this standard to determine what action should be taken. After thorough analysis and careful deliberation, the NPSH review committee recommended that a complete revision of the standard be undertaken and that the 1998 version be withdrawn until the new standard is approved. ANSI was advised that ANSI/HI 9.6.1-1998 should be withdrawn immediately and that HI could no longer distribute or support the document. The official public announcement appeared in the October 24, 2003 edition of ANSI Standards Action, a weekly ANSI publication. 字串9
A new, totally revised NSPH Standard is under development by the NPSH Committee and will be entering the review process soon. The committee is aware that the replacement document is urgently needed and has been working diligently since 2002 to develop a new document. They want to be sure that it is accurate, complete, and addresses the needs of the pump community. It will contain considerably more tutorial information than the 1998 standard and will respond to the questions most often posed by those involved with pumps and NPSH.
It is anticipated that it will require at least another year to complete the process and the new NPSH Margin is available for purchase. I wish that HI could offer you an equivalent or replacement standard, but to my knowledge no other NPSH Margin Standard exists.
I hope that this information is helpful. Thank you again for contacting the Hydraulic Institute.
Mary Silver
Director, Marketing & Membership 字串7
Hydraulic Institute
UNQUOTE
insult2injury (Mechanical)
10 Dec 08 9:14
Don't forget that specifying too much NPSH margin may not be desirable either as it could have adverse affects on the pump/system. I2I
Artisi (Mechanical)
10 Dec 08 14:54
"The committee is aware that the replacement document is urgently needed and has been working diligently since 2002 to develop a new document."
Pleased to see they are treating this with some urgency it should be finished within another year, wow - only 7 years or so to revise a standard.
insult2injury makes a good point re specifying too much margin - hydraulically there shouldn't be a problem but it can put you into a bigger pump /motor operating away from BEP - hence my suggestion of checking with the manufacturers or operators of the same equipment in similar installations.
字串4
athomas236 (Mechanical)
11 Dec 08 4:23
Artisi,
I agree with your sentiments and I still do not really know why 9.6.1 was withdrawn.
My problem is that I am investigating the case of a 3x350MW coal fired sub-critical plant where the EPC contract says the BFP NPSH margin should be 1m or 10% whichever is greater and a bank's engineer who says it should be 80%.
At the moment I am proceeding on the basis that the EPC contract requirements apply to both continuous and transient conditions such as following a turbine trip and and the bank's engineer's requirement applies only to continuous operation.
I2I,
I am not exactly clear how "too much NPSH margin" can cause adverse effects except as mentioned by Artisi.
Best Regards,
athomas236
Artisi (Mechanical)
11 Dec 08 5:19
athomas236 字串9
Guess you need to clarify that you are comparing apples with apples as to what/where the margin is to be applied.
For interest, what size units, type and configuration are you talking about and is this a new or existing installation?
There are a couple of regular posters who will have good first hand experience in this area - for your sake let's hope they see this post.
insult2injury (Mechanical)
11 Dec 08 8:58
Without knowing the specifics of the plant, 10% is probably too low and 80% is most likely overkill on the margin. Most that I've been involved with operated in the 30%-50% range. You need to look at NPSH not only at design conditions but also at runout. Also confirm whether the margin is stated in terms of the 3% NPSH.
Excessive margins lead to larger pumps with larger suction passages. The larger suction passages allow for a lower NPSHR, but result in higher suction specific speeds. Since the suction is oversized, suction recirculation (and probably discharge too) will commence at much higher flowrates limiting the range of operation. With boiler feed pumps/deaerators you also have to consider transient operation during load swings/abnormal trips/etc. I2I
字串2
athomas236 (Mechanical)
11 Dec 08 10:40
Artisi and I2I,
Once again thanks for your responses.
I received ANSI/HI 9.6.1 today and have to admit that for £70 I was disappointed with the standard. It looks as if the first draft could have been a useful document but it was watered down during the committee discussions.
I was particularly disappointed by the statement that Fig 3, which is used to determine if the suction energy is low, high or very high does not apply to multistage pumps such as used for boiler feed pumps.
I have today ordered the 2nd edition of Pump User's Handbook, Life Extension in the expectation that one of the authors (Allan Budris who was also chairman of 9.6.1 committee) will provide more information in the book than he was able to do in the standard.
I agree with the points about apples and apples, looking at run out conditions and 3% NPSH. 字串3
All I know about the project at the moment is that there will be 3 by 60% BFPs per unit and each unit will have an output of 350MW gross and the project is a new build.
Best Regards,
athomas236
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