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Author Topic: Asleep at the Wheel ? - API RP11S2  (Read 20 times)
DavidPDavidson
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« on: August 07, 2008, 05:36:20 PM » Reply with quote

It's amazing who you meet on the airplane and the things you talk about, isn't it?

Flying home and happened to sit next to a senior engineer with a major Houston based engineering contractor. Seems they've recently been contracted by a major operator with a production operating agreeement in Brazil. His engineering company is to provide project management and engineering/testing supervision and approvals for a significant ESP contract award with one of the Big 3 ESP manufacturers in Oklahoma.

He is one of the engineers and inspectors to oversee a first article Sub Sea pump system, with one of those 1500 hp esp motors. This is known to be state of the art for the ESP industry in terms of motor horsepower ( and getting rid of all that heat), thrust handling (those big pumps create lots of thrust- that cycles too ), stage design, and coating systems, and all the other engineering issues you would see in a subsea application.

Anyway, we all know about first articles, and that's the way progress happens. First articles are always exciting and full of new problems to solve.

But our conversation was not about the subsea environment, nor the efficacy of a 1500 hp motor, fluid characteristics, VSD drive systems, starting characterisitics for high HP applications, gas handling, emulsification issues, abrasives, pump curve operating limits, thrust concern / bearing systems, and or any other of the various subjects and quandries that ESP engineers commonly discuss.

It was about standards. And testing. And specifications.

It seems that the ESP industry and API haven't done much since the first draft of API RP11 was being negotiated by oil & gas operators and esp manufacturers back in the mid - 1980's.

And has anything changed in the esp industry since 1985 ?

I think so. Things have changed a lot. But not much with API Standards.

Which makes you wonder? Are operators asleep at the wheel? And do operators understand the financial and operating consequences?

This engineer was lamenting how there's not much substance to the testing standard in terms of inspection in API RP11S2. In fact, it's void of most anything.

The entire recommended practice is exactly 12 pages. The first 5 pages are title pages, outline, forward, special notes - in other words empty pages. The last page (page 12) is nothing more than an API logo, and an order number G11S22 to make it real easy to say what you want when you call API to order it.

What's in between, is ... well , - who remembers the classic Wendy's hamburger advertisement by the cranky old lady - she exclaimed.  " WHERE'S THE MEAT?!?"

My new found engineering buddy on the flight was flabbergasted! Never before in his career had he ever seen anything like this. Had the manufacturing industry been pulling the wool over API's eyes and also been able to blind the oil & gas operators?

In reviewing all the subclasses 1,2,3,4,5,6 of API RP11S relating to the ESP, there's really very little pump material, manufacturing tolerance, and testing standards with tolerances that have normal rotating equipment performance metrics.

We're talking about a subsea application, a multi billion dollar project with very high visibility, and significant intervention costs and of course, billions of dollars of revenue stream, ... and the pumps to produce the oil have

API RP11S2  AS THE TESTING INSPECTION STANDARD !   OUCH! Could anything less comprehensive as an inspection standard be imagined!

I had to concur. Anybody who knows anything about esp's and their performance characteristics through the years knows what the backgrounder is about this.

He pulled his copy of API RP11s2, and I've got to say our conversation became quite interesting and rarified from there on. Made the flight go by fast, and I just hope we did not bore the passengers around us too much.

So what does the standard comprise?

After some definitions of terms and a review of simple hydraulics and the affinity laws, etc, you get down to 4.9 that talks about instrumentation accuracy during testing. By the way, it really made us wonder how the esp manufacturers promote all this great accuracy for their new down hole monitoring gauges, but the flow and pressure accuracy during testing at the factory are far more lenient with wider tolerance ranges, than all that new equipment can measure downhole? See an extract of API RP11S2 below.  Hmmm, got to think what's up with that one! That's a wake up call, isn't it?


And the real meat ... ahem ... the real meat TEST CERTIFICATION in Section 5, well, - that really tells the story! Better set the alarm clock with both the radio and buzzer set for high.

How about:

Pump test acceptance levels of :
Head - flow rate  plus/minus 5% head AND  plus / minus 5% flow rate.  OUCH!

BHP - flowrate  - a whopping plus / minus 8 % allowance !!!

Pump efficiency - flow rate  - get this, who would believe it in today's world - 90% of efficiency at rated flow!!!

Operators, do you know what all the above parameters translate to in terms of pump performance, for a 1500 hp system?


Extract from API RP11S2

But you know what, after that, - the rest of the standard was just a pump curve example and two charts showing acceptance level bands on a sample curve.

How was he supposed to provide acceptance based on this loose and empty standard ? 
And most important, wasn't approval rather insignificant since there is so much latitude for performance misses? In addition, how could the operator possibly accept such wide margins of non compliance for pump and power efficiency performance? The performance standards of a pump specification like API 610 are the norm, and why should ESP pumps be able to get away with so much less?


Flight attendents came by to make sure seats were in the upright position and prepare for landing.

We hurriedly jotted down notes and an outline of what the API standards should contain, and promised to meet up again and see what can be done.

Before sharing our outline and suggestions for a real inspection standard, what do you think about the current standard? Does it need to be revised? What changes would you recommend?

How about posting your thoughts. Or give me a call, or send me an email. Let's do something about it.

Until next time,
DavidPDavidson
my email is :  dpdavidson at gmail.com
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David P Davidson
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« Reply #1 on: August 10, 2008, 07:35:42 AM » Reply with quote

David,

Many are aware of the background that prompted the pump testing RP being developed so I will not bore anyone with those details.  Suffice it to say something WAS needed and what was developed was far better than nothing at all.

However, comparing RP11S2 to API 610 ignores the practical.  The pump performance limits, that might seem excessive, are primarily to account for the very low flow stages.  These have very small vane openings and consume very little horsepower (per stage).  Consequently small manufacturing tolerances have proportionally greater performance effects on these stages than the higher volume stages.  Meeting the RP performace requirements on a 200 B/D pump does require some significant care in day to day manufacture.  Meeting them for a 10000 B/D pump requires much less care.

An improvement to the RP might be to adjust performance limits based on flow rate. The higher the flow rate the tighter the limits.

Regarding the instrument accuracies....back in the day when this RP was developed many manufacturers were testing pumps in vertical "test wells" and using "calibrated" motors to do their pump performance testing. Consumed electrical power by the motor was monitored and pump HP was derived from the motor's "calibration"curve.  These "calibration" curves were many times rather crude and not very accurate.  However even if properly done typical motor HP output measurement is limited to about +/- 2% accuracy.  Many manufactueres now use submerisible torquemeters to improve the measurement of consumed pump horsepower when testing vertically.  Horizontal test benches also typically use torquemeters but these benches are usually limited in both flow and power and therefore are not suitable for very high flow/large HP pumps.  Bottom line is that the HP tolerance band could be narrowed due to better measurement techiques that have been developed since the original RP came out.

Also remember that ESP pumps can have hundreds of stages (unlike the typical API pump).  ESP pumps could very well meet stricter performance levels but the quality cost would be enormous and not justifiable for many applications.

Additionally remember that RP 11 is a "recommended practice". Operators have the option of requiring it as specification, not requiring it, or requiring a stricter specification.  In the subsea application you referred to and for the size equipment (1500hp) cited it would certainly make sense to included a higher quality requirement as part of the contract award.  This would not necessarily make sense for an onshore 300 B/D benign application.

   
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« Reply #2 on: August 10, 2008, 08:04:53 PM » Reply with quote

Gentlemen,

Both substantive and well written comments.

Thank you.

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DavidPDavidson
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« Reply #3 on: Today at 09:08:34 AM » Reply with quote Modify

David,
An improvement to the RP might be to adjust performance limits based on flow rate. The higher the flow rate the tighter the limits.

Regarding the instrument accuracies....back in the day when this RP was developed many manufacturers were testing pumps in vertical "test wells" and using "calibrated" motors to do their pump performance testing. Consumed electrical power by the motor was monitored and pump HP was derived from the motor's "calibration"curve.  These "calibration" curves were many times rather crude and not very accurate.  However even if properly done typical motor HP output measurement is limited to about +/- 2% accuracy.  Many manufactueres now use submerisible torquemeters to improve the measurement of consumed pump horsepower when testing vertically.  Horizontal test benches also typically use torquemeters but these benches are usually limited in both flow and power and therefore are not suitable for very high flow/large HP pumps.  Bottom line is that the HP tolerance band could be narrowed due to better measurement techiques that have been developed since the original RP came out.

Also remember that ESP pumps can have hundreds of stages (unlike the typical API pump).  ESP pumps could very well meet stricter performance levels but the quality cost would be enormous and not justifiable for many applications.

Additionally remember that RP 11 is a "recommended practice". Operators have the option of requiring it as specification, not requiring it, or requiring a stricter specification.  In the subsea application you referred to and for the size equipment (1500hp) cited it would certainly make sense to included a higher quality requirement as part of the contract award.  This would not necessarily make sense for an onshore 300 B/D benign application.   

Agreed - good comments - appreciate it.

1. Regarding limits for different size pumps - YES, exactly. We'll work on this.
2. Regarding instrument accuracies - Agreed industry can do much better. What's the incentive for industry to do this on their own, without prodding from operators? Nil - that's probably why it hasn't been done.  We'll work on that.
3. Regarding quality standards costing more. Reply - what are lack of meaningful performance quality standards costing operators? Answer - I believe a study can justify the investment many times over.

HP sizes of pumps - many API 610 pumps are under 100 hp. So relative size I don't believe is a good argument for not having a standard for ESPs.

ESPEngineer - if you'd like to do an SPE paper with me, please let me know.

I am in contact  with the engineering company, and we can write real specifications for the various esp sub assemblies. I know they want it. If industry wants to use it, so much the better. Hopefully this forum will allow volunteers to step forward and help also. Also publicize the effort, and make it real easy to distribute by way of this website or other.

I can think of standards that I believe need to be written for:

1. The pump
2. The seal section
3. The motor
4. The VSD - what exists today for mfg standards, and testing? Best I understand, the complete product lines don't  have UL certifications - correct me if needed. How many ESP industry VSD's are operating for example in the safety stringent North Sea? Ever wonder why?
5. Cable standards. More new cable manufacturers entering this market besides the old Pirelli and CL Cable plant. Standards will be needed, and may as well get it done.

Anybody like to get involved, my email is  dpdavidson at gmail.com

Best Regards
David



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David P Davidson
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