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Nilesh
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NPSHR 40000 Hrs for Centrifugal Pumps

03/18/2010 2:29 AM

What is NPSHR 40,000 Hrs and how it can be calculated ?

I do not find any details in API 610 1Oth Edition and even not available in Pump hand book.

One of the Client requirement says that : " For all Pumps, NPSHA in the "Preferred Operating Region" shall be equal or greater than NPSHR 40,000 Hrs"

Can any one provide more details about NPSHR 40,000 Hrs and how it can be calculated OR which parameters shall be considered for the calculation of NPSHR 40,000 Hrs. etc....

How it is diff. from the NPSHR values generally vendor mention in API Data sheet ?

Pump selected with NPSHA - NPSHR > or = 1 meter @ rated point that is technically acceptable as per API 610, But, can this NPSHR 40,000 Hrs. requirement change the acceptance of the same pump !!!

With regards,

Nilesh.
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Pathfinder Tags: 000 Hrs for Centrifugal pumps NPSHR 40
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Kaisan
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#1

Re: NPSHR 40000 Hrs for Centrifugal pumps

03/18/2010 3:22 AM

"NPSHA in the "Preferred Operating Region" shall be equal or greater than NPSHR 40,000 Hrs"

Go back to your client and ask him to correct his specification. The sentence is patently nonsense.

NPSHa should, in my opinion, always be higher than NPSHr by at least 1m, but if he accepts "equal to", so be it.

As for it being 40,000 hours that is just a cut and paste error.

It may be that he wants to achieve 40,000 hours MTBR (5 years), which is not unrealistic if he is buying API610 pumps and you get things like NPSH margins correct..

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Nilesh
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#10
In reply to #1

Re: NPSHR 40000 Hrs for Centrifugal pumps

03/24/2010 2:32 AM

Refer reply from Mr. Cadman and update your knowledge.....

I hope, you will think twice now before replying to any technical question.

Regards,

Nilesh.
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roto king
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Posts: 16
#2

Re: NPSHR 40000 Hrs for Centrifugal pumps

03/18/2010 5:38 AM

Hehehe..NPSHR is 4000k HrsGood Joke...Dear NPSHR is net pump suction head required which is the requirement of Pump selection and operation for preventing it to operate....You ask him what is NPSHa then ask your pump vendor to do selection on NPSHa ...NPSHa>NPSHr
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Nilesh
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#11
In reply to #2

Re: NPSHR 40000 Hrs for Centrifugal pumps

03/24/2010 2:33 AM

Refer reply from Mr. Cadman and update your knowledge.

Regards,

Nilesh.
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coconutpete
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#3

Re: NPSHR 40000 Hrs for Centrifugal Pumps

03/19/2010 12:59 AM

I am a bit inclined to agree with Roto King is this some kind of Joke? If not i would suggest that you should find another ocupation which has nothing to do with Engineering. NPSHr is Net Positive Suction Head Required and is a fgure given by the pump manufacturer. It cannot be calculated. NPSHa is net positive suction head available. This can be calculated by the engineer. I dont intend to tell you how to do this but it is very simple.

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Nilesh
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#4
In reply to #3

Re: NPSHR 40000 Hrs for Centrifugal Pumps

03/19/2010 3:33 AM

Question is not what is NPSHA and NPSHR....that is simple and clear

as mentioned, Pump is selected accordingly

Qustion is related to NPSHR40,000 hrs....How it can impact the pump already selected with NPSHA-NPSHR margin1 meter @ rated point ..

Important is to know why Client is asking "NPSHA in the "Preferred Operating Region" shall be equal or greater than NPSHR 40,000 Hrs".

Do you have ever come across NPSHR40,000 Hrs requirement...!!! If not please do not reply and just read this Forum to get more details from any expert who has experience to selecte Pump with NPSHR40,000Hrs. criteria also.

With regards,

Nilesh.
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Anonymous Poster
#5
In reply to #4

Re: NPSHR 40000 Hrs for Centrifugal Pumps

03/19/2010 10:37 AM

This goes back to the old "Garbage in, garbage out" theory. Like the previous contributor said "Go back to your customer for clarification." Someone obviously screwed up when typing the spec and NPSHR at the mid operational point got blown into some 40,000 hrs. Looks pretty much like an old fashioned typo by a Process Engineer or their assistant.
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Anonymous Poster
#6
In reply to #5

Re: NPSHR 40000 Hrs for Centrifugal Pumps

03/19/2010 11:21 PM

As you and Kaisan have said - "typo" - "cut and paste error"
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Nilesh
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#7
In reply to #5

Re: NPSHR 40000 Hrs for Centrifugal Pumps

03/21/2010 11:39 PM

This is not a typing mistake...

This is a client requirements and TWO of the Pump Vendor has confirmed the NPSHR 40,000 Hrs. but, vendors refused to divulge calculation declaring it as their knowhow.

If no one is interested in NEW THINGS, and it seems no one is aware about this NEW REQUIREMENTS, I will seach in other forum.
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JSCadman
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#8
In reply to #7

Re: NPSHR 40000 Hrs for Centrifugal Pumps

03/23/2010 9:16 PM

From an article by Terry Henshaw, P.E. in Pumps & Systems -

http://www.pump-zone.com/pumps/centrifugal-pumps/suction-specific-speed-part-three-using-suction-specific-speed-to-establish-adequate-npsha.html

A number of technical papers (1, 4, 7, 8) have shown that the maximum damage rate to centrifugal pumps, at least in water services, typically occurs when the NPSHA is in the range of two to three times the NPSHR3. Therefore, although providing additional NPSHA will increase pump head and efficiency, it will also push the NPSHA toward, or into, the range where maximum erosion rate occurs to the impeller.

Vlaming (3) concluded that it was not reasonable to eliminate all cavitation in an impeller, and settled on 40,000 hours (five years) as a reasonable life of an impeller. His NPSH recommendations for obtaining 40,000 hours with a properly designed, stainless steel impeller pumping cool water can be condensed to the following equation:

NPSHR40K = 1.2 (13‑8)

This equation applies only to the capacity (flow rate), which results in non‑prerotating, shockless entry of the pumpage into the impeller vanes.* That capacity is normally about 20 percent higher than the best efficiency capacity, but can be even higher (1).

Equation 13‑8 can be rewritten, in terms of U1 and β1, as follows:

NPSHR40K = (13‑9)

Converting to suction specific speed results in:

S40K = 8150 (13-10)
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Nilesh
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#9
In reply to #8

Re: NPSHR 40000 Hrs for Centrifugal Pumps

03/24/2010 2:30 AM

Thanks.

I hope now all other members will also take note of this NEW INFORMATION and update their knowledge.

Regards,

Nilesh.
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Codemaster
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Location: Stoke-on-Trent, UK
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#14
In reply to #9

Re: NPSHR 40000 Hrs for Centrifugal Pumps

08/29/2019 12:38 PM

I tried to find those docs on the web, but without success. I assume you’ve looked into this as you have a spec to meet, and that the various parameters are defined, along with the units.

I’m not clear what the formulas are telling us. It looks like a calculation for NPSHR (whether 40K or otherwise). But NPSHR is normally provided by the pump manufacturer, determined by test work. What do you do if the figures disagree (or even if they don’t!)? Be interested to see results if you’ve done any calculations. The text in #8 says too much NPSHA causes more cavitation, but that can be limited to 2-3 x NPSHR using the manufacturer’s NPSHA.

Also I’m not sure “providing additional NPSHA will increase pump head and efficiency”. Clearly it will increase discharge head, but not generated head. The NPSHR test gives the figure at which flow falls by 3%, at a fixed pump differential head. But with the usual NPSHA margin of 1m minimum over the stated figure, the fall will be lower, and increasing NPSHA unlikely to increase efficiency, either volumetric or the more usual water power/shaft power.

What do you think?

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Codemaster
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#15
In reply to #14

Re: NPSHR 40000 Hrs for Centrifugal Pumps

08/29/2019 4:01 PM

Correction - "....but that can be limited to 2-3 x NPSHR using the manufacturer’s NPSHA" should be "....but that can be limited to 2-3 x NPSHR using the manufacturer’s NPSHR."

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crusader911
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Join Date: Jan 2008
Posts: 29
Good Answers: 1
#12

Re: NPSHR 40000 Hrs for Centrifugal Pumps

03/24/2010 8:20 AM

This is very interesting, but one should take care in applying it. I have not read the papers cited, but the poster was careful enough to note that the 40K concept was specific to water service and that the formulas presented were for stainless steel impellers.
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rumblefrog
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Join Date: Aug 2019
Location: Milwaukie, Oregon USA
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#13

Re: NPSHR 40000 Hrs for Centrifugal Pumps

08/22/2019 6:58 PM

I have a copy of a paper published in 1983, titled Advanced NPSH Estimates for Centrifugal Pumps. This paper was published by ARAMCO Overseas Company. It has a a reference number of AER-2319 / TSI 53-137.

The paper provides extensive research and formulas base around calculating a "40,000 Hour" impeller cavitation life. I have used the contents over the past 32 years as part of my impeller suction design procedure.

Regards,

William Carnes, P.E.

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PWSlack
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#16

Re: NPSHR 40000 Hrs for Centrifugal Pumps

08/30/2024 6:25 AM

<...seach in other forum...>

How did that go?

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Anonymous Poster (2); coconutpete (1); Codemaster (2); crusader911 (1); JSCadman (1); Kaisan (1); Nilesh (5); PWSlack (1); roto king (1); rumblefrog (1)

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