Comprehensive Pump Testing Challenges

1
Comprehensive Pump Testing Challenges

2
Purpose

• This presentation will discuss
• Hardships encountered while implementing
  comprehensive pump test requirements.
• Benefits that may be realized if the
  comprehensive pump test (CPT) requirement is
  eliminated in favor of a Group A tests conducted
  at the same flow rate.
• A historical review related to the origin of the
  CPT.

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Background

• The requirement to conduct a Comprehensive Pump
  Test became mandatory with the NRC endorsement of
  the 1995 Edition of the ASME OM Code, including
  the 1996 addenda.
• Since that time, the NRC has received many
  requests for relief, however, not all of these
  requests were for the anticipated reason.
• The expected request dealt with the
  impracticality of performing the test due to the
  inability to achieve the desired flow rate.
• The unexpected requests revealed that utilities
  did not see a corresponding increase in the level
  of safety or quality based on the additional
  costs associated with the development,
  implementation and maintenance of a new test and
  procurement of new instruments.
• This was based on the fact that most quarterly
  Group A tests were already being conducted at the
  required CPT flow rate.

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Background

• The various issues associated with the CPT were
  brought to the attention of the ASME OM Code
  Committee.
• The Committee agreed that changes were necessary.
• Revisions to the Code have been proposed, but not
  approved.
• A White Paper was developed to support the
  requested change.

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Background

• What are the issues?
• First, an attempt to understand why the CPT was
  developed is necessary.
• It must be understood that this is my opinion
  only and is based on previous writings and
  attendance at OM Code meetings and symposiums
  since 1996.
• I was not involved with ASME during the time that
  the original discussions began during the late
  1980s and early 1990s.

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Background

• Papers were presented at the second and third
  NRC/ASME symposiums, and a letter was written by
  the NRC to the OM Chairman regarding the need
  for a design basis test.
• These documents cover the late 80s and early 90s.
• The NRC wanted a test that was more effective in
  detecting pump degradation and that was capable
  of assuring the design basis capability of the
  pump.
• Essentially, there was concern about the ability
  to correlate degradation at minimum flows to the
  operability.
• The NRC was also concerned about pump damage that
  could occur by testing on minimum flow.
• Both the NRC and the ASME Working Group felt that
  this new test needed to be practical and not task
  plant resources.
• Because the test was more difficult, it would be
  conducted at an infrequent interval.
• It was decided that there was an urgent need to
  develop a comprehensive pump test.
• This test would provide a better evaluation of
  pump characteristics at a reduced frequency.
• The OM-6 working group agreed to develop a CPT
  meeting the stated objectives.
• With this understanding, the NRC accepted the
  expanded upper hydraulic range from 3 to 10.
  The expanded limits were introduced in OM-6.

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CPT Challenges

• As the CPT was being developed, ways to improve
  the test were reviewed and it was discovered that
  the only practical instrumentation improvements
  that could be made was associated with pressure
  (differential pressure).
• Requirement was reduced from 2 to 1/2.
• The hydraulic requirement was changed to require
  that the pump be operated at or near design flow.
• Due to the hardship involved with installation of
  more accurate test instruments, the test would be
  performed during shutdown conditions.

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CPT Challenges

• Positives and Negatives associated with the CPT.
• Positives
• Testing at Design Flow makes it easier to
  determine the operability of a pump when
  degradation occurs.
• More accurate pressure instrument results in more
  margin.
• A more accurate pressure gage reduces the amount
  of error included in development of the minimum
  performance requirement.
• Typically, the accident performance requirement
  is artificially elevated to incorporate the error
  associated with the test instruments.

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CPT Negatives

• Cost
• Plant modifications or processing of relief
  requests will be needed if the required test flow
  cannot be achieved.
• Potential reduction in safety system availability
• Due to small hydraulic improvements.
• Potential to increase dose and maintenance costs
• Due to small hydraulic improvements.
• Increased procurement, implementation and
  maintenance costs
• More accurate pressure devices cost more.
• Additional procedures are necessary.
• More engineering work will be necessary.

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CPT Negatives

• Potential for testing with less repeatability
• High accuracy pressure gages cannot be left in
  place and must be removed following testing.
• Post maintenance test issues
• Related to establishing reference values for the
  associated Group A test.
• Which test do I run following maintenance?
• More subjectivity
• What is the Engineer supposed to do in the event
  that a pump has passed the normally scheduled
  Group A test, but would have failed the CPT if it
  had been performed?

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CPT Challenges

• It is also important to point out that the
  pressure instrument is the ONLY equipment change
• This concept is commonly misunderstood.
• Some documents indicate that the CPT requires the
  use of more accurate flow instrumentation (ref
  NUREG/CP-0152, Vol. 4, page 3A-43).
• This position has also been misstated in public
  meetings and forums.
• In reality, the flow rate, speed and vibration
  instrument requirements for a CPT and a Group A
  test are identical.

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CPT Challenges

• CPT improvements were limited to
• Requirement to test within 20 of design flow.
• Pressure (differential pressure) gage accuracy
  improved to 0.5.
• The hydraulic required action limits were reduced
  from 1.10 x reference to 1.03 x reference.
• Note that this change only involves the upper
  required action range. The lower required action
  range for all pump types did not change.

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CPT Challenges

• There is no argument that testing a pump at
  substantial flow provides a better overall
  assessment of both the hydraulic and mechanical
  pump condition.
• With that understanding, many plants routinely
  test their pumps at substantial flow conditions
  consistent with the intent of a CPT, when
  practical.
• Therefore, if the substantial flow condition is
  being met, what advantage is there to conducting
  a biennial CPT?
• The only outstanding differences are the accuracy
  of pressure gage and the difference in the upper
  acceptance limits.

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CPT Challenges

• Another change that is overstated deals with the
  use of the term more restrictive acceptance
  criteria.
• The fact is that the limits for a CPT are not
  more limiting when compared to the Group A test
  with respect to degradation.
• The lower bounding (required action) limits for a
  Group A test and a CPT are IDENTICAL.

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CPT Challenges

• The only hydraulic limit change involves a
  reduction from 10 to 3 of reference.
• The use of a 3 upper limit may impose a
  unwarranted problem for which there is no clear
  answer.
• With the restricted upper limit, it is quite
  possible to easily pass the routine Group A test,
  yet find that a CPT would have been unacceptable
  due to high flow rate or differential pressure.
• This places the engineer in a precarious
  position.
• Initial guidance regarding this issue suggested
  that engineering judgment would apply.
• More recent guidance provided at the 2004
  NRC/ASME Symposium indicate indicates that the
  problem should be resolved prior to the conduct
  of the CPT.

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CPT Challenges

• The fact is that there may be no problem to
  correct.
• A 3 test deviation (or 1.03 x reference) is not
  unrealistic given the allowable ranges and
  instrument errors associated with an inservice
  test.
• As previously indicated, the Code instrumentation
  requirement for flow rate did not change.
• The allowable flow error is 2 of full scale,
  with the full scale being limited to three times
  the reference value. Under worst case
  conditions, this could yield a worst case error
  of 6.

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CPT Challenges

• A 6 flow rate error can easily cause a test to
  exceed the 3 upper limit. Bear in mind that
  other factors have not been considered in this
  scenario, such as
• Pressure indicator error and the effect of the
  performance point on the pump curve
• Temperature drift
• Mechanical error contributions (orifice plate,
  venturi tolerances, etc.)
• Parallax error
• MTE calibration tolerances
• Test data fluctuations
• Meter readability IEEE requirements of ½ the
  smallest increment
• Allowable variance around the reference point.

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CPT Challenges

• In addition, if a pump fails a CPT due to
  exceeding the 3 upper limit, the pump must be
  declared inoperable and corrective actions
  implemented or the condition evaluated.
• The net effect of this action is a reduction in
  safety!
• Corrective actions will increase maintenance and
  operating costs and may introduce unwanted
  errors.
• Declaring a pump Inoperable as a result of an
  improved hydraulic condition is a very
  difficult requirement to implement.
• Given the fact that many IST pumps may DEGRADE at
  least 7 before actions are required, and
  centrifugal pumps can degrade by as much as 10.
  

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CPT Challenges The 3 upper limit

• There is no rational explanation as to why the
  Code would require a more critical assessment of
  pump performance due to elevated flow or
  pressure.
• Excessive pump improvement can be indicative of a
  potential problem however, these cases are
  extremely rare.
• Trending of pump performance (increasing or
  decreasing) is now a requirement of the Code.
• The 3 upper limit was in place up until the
  adaptation of the 1988 ASME OM Code edition, at
  which point the upper hydraulic limit was
  increased from 3 to 10.
• To supplement this change, a white paper was
  developed and discussed the changes and the basis
  for these changes.

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CPT Challenges The 3 upper limit

• With regard to the elimination of the 3 upper
  hydraulic limit, the discussion centered on the
  fact that more emphasis was being placed on
  vibration measurement as the primary indicator of
  pump degradation. This was based on measuring
  vibration in velocity mode (inches/sec), vice
  displacement (mils).
• This change was brought about because there was
  concern relative to the ability to detect a
  change in pump performance based on hydraulic
  parameters.
• Consequently, it was determined that vibration
  measurement (using the new method) would be more
  sensitive to changes in pump performance.
• It was stated that use of this technology would
  reduce the number of pumps requiring increased
  testing or corrective action based on erroneous
  (hydraulic) test results.

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CPT Challenges The 3 upper limit

• Thus, the extent of the change was to allow
  equipment to be run in a window hydraulically
  and then to evaluate pump performance more
  closely with vibration.
• The window serves two purposes.
• First, it ensures that the pump is performing its
  primary function of pumping liquid and
• Operated in a narrow band where the vibration
  data will be repeatable.
• It was also recognized that positive displacement
  and vertical line shaft pumps could not be
  treated the same as centrifugal pumps. Thus, the
  hydraulic limits for degradation were not changed
  for these pump types.

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CPT Challenges The 3 upper limit

• The 3 upper limit was re-instated in the 95
  edition of the OM Code.
• It has been published that the reduced upper
  limit ensures that the test results are not
  impacted by erroneous instrumentation.

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CPT Challenges

• The goal with the development of a CPT was to
  establish a more thorough and vigorous biennial
  test supplemented with less rigorous quarterly
  tests.
• However, if a Group A test is performed at the
  CPT flow rate, only the Group B pump test, by
  eliminating the requirement to measure vibration,
  would qualify as a less rigorous test.
• The Group B pump population is small.
• Pumps that are operated only to implement IST
  requirements for periodic testing.

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CPT Challenges

• It is commonly stated that the CPT is a more
  rigorous test that is supplemented with a
  periodic Group A or B test using more relaxed
  acceptance limits and less rigorous requirements.
  In reality
• The Group A and B test hydraulic acceptance
  limits for Operability DID NOT change from the
  previous edition of the Code.
• The Group A test mechanical acceptance limits for
  Operability DID NOT change from the previous Code
  edition.

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CPT Challenges

• The only pumps subjected to less rigorous testing
  were the Group B pumps by eliminating the
  requirement to measure vibration at a quarterly
  interval.
• The instrument accuracy requirements for flow
  rate, speed and vibration DID NOT change.
• All pumps were now required to be tested at
  design flow by development of the CPT.
• This alleviates previous concerns related to
  correlation of minimum flow test results to
  design basis capability. Specifically, the
  effect of various degradation mechanisms on the
  shape of the curve could not be predicted.

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CPT Challenges Pressure indication

• The pressure (differential pressure) instrument
  accuracy was reduced from 2 to ½.
• The basis for this change was to provide more
  accurate reference values.
• It was published that the instrumentation
  requirements were identical to those established
  for the preservice test.
• As a result, it would be easier to detect
  degradation during subsequent tests based on the
  fact that you would be comparing pump performance
  using the same instrumentation and reference
  point that was established during the preservice
  test.
• It has been stated that another driving force
  behind the ½ gage was due to the fact that the
  test was only conducted every two years.
• Does the improved pressure instrument accuracy
  provide better long term trending capability?
• In my opinion
• NO!

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CPT Challenges Pressure indication

• Heres why?
• Repeatability Trend capability
• Sensitivity
• Actual accuracy
• A more accurate pressure instrument may yield
  less positive attributes with respect to
  repeatability.
• The gages are more sensitive and prone to failure
  if left in service therefore, are removed and
  transported to and from the test site.
• The gage is then installed, vented and zeroed
  (for many test gages) prior to use.
• Interpretation of the result may also lead to
  inconsistencies as a result of the increased
  sensitivity of the device, which would tend to
  result in more active needle oscillations,
  forcing the reader to employ averaging techniques
  if the oscillations cannot be dampened.
• The increased sensitivity also increases the risk
  of impacting the calibration of the instrument
  due to physical agitation when in transit,
  installed or removed.

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CPT Challenges Pressure indication

• This could result in a calibrated gage appearing
  uncalibrated, or vice versa.
• In short, a test using a more rugged, permanently
  installed gage may offer better long term trend
  capability when compared to the more accurate,
  but less rugged test gage.
• Realized accuracy
• Although installed gages are certified to an
  accuracy of 2, I have found that they are
  actually accurate to at least ½ based on a
  review of as-found calibrations and discussion
  with our IC department.
• In fact, we are looking at increasing our
  calibration interval based on the success of our
  as-found calibration checks.
• It would be interesting to see if a review of
  industry calibration records yield a similar
  result.

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CPT Challenges - Summary

• Implementation of the CPT requirements may
  produce unwanted outcomes for those utilities
  that already meet the primary intent of a CPT by
  testing their pumps at design flow.
• When you update your program and begin
  implementing the CPT requirements, you can expect
  the following
• Challenges from the plant staff (Operations,
  Maintenance, Procedures, Management) regarding
  the value of this additional test.
• Additional workload associated with maintaining
  and updating two sets of reference values and
  assignment of post maintenance test requirements.
  
• Emergent work and reduced safety system
  availability At RNP, the upper acceptance limit
  has been exceeded on two occasions. This
  required that pumps be taken out of service. See
  bullet 1 for additional effects.
• Budget for additional cost RNP spent
  approximately 22,000 on new pressure gages.
• NRC denial of your proposed request to use the
  Group A test at the CPT flow rate in lieu of the
  CPT.

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CPT Challenges - Summary

• It is my belief that a quarterly Group A test
  conducted at the CPT flow rate is more effective
  in evaluating pump performance and detecting
  degradation compared to the conduct of a CPT at a
  biennial interval supplemented with a quarterly
  test at a lower flow rate.
• The pump is tested to an identical hydraulic
  load.
• Vibration, flow rate and speed instrumentation
  requirements are identical.
• The lower bounding hydraulic limits are
  identical.
• The mechanical limits are identical.
• More frequent testing at higher flow rates (using
  the same test equipment) provides a much better
  trend capability.

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CPT Challenges - Summary

• If a quarterly test is conducted at the same flow
  rate as a CPT, then
• The primary concerns related to verification of
  operability and detection of degradation are no
  longer valid.
• This was the primary motive for developing the
  CPT.
• A test gage is not necessary.
• Since the equivalent test is being performed
  quarterly, there would be no need to obtain more
  accurate data every two years.
• In reality, the more accurate gage may not offer
  better accuracy, or repeatability.

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CPT Challenges - Summary

• The reduced upper hydraulic acceptance limit is
  not necessary.
• Because the equivalent test is performed
  quarterly, there is no need to tighten the upper
  limit to counter the effects of instrument error.
• There is no equivalent criteria for degradation,
  which is the prevalent failure mechanism.
• You are required to trend performance.
• The improved vibration requirements that resulted
  in the previous expansion of the upper limit are
  still in place.
• The upper criteria could be exceeded due to
  normally expected instrument error allowances.

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CPT Challenges - Benefits

• The benefits associated with this proposal are
  many.
• First and foremost
• Better assessment of overall pump performance.
• Better trend capability.
• Improved ability to detect degradation.
• Reduced capital costs.
• Accurate pressure gages are expensive.
• Reduced OM costs.
• Installation and maintenance of test gages.
• Develop, maintain and update additional
  procedures.
• Engineering evaluation using two sets of
  criteria.

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CPT Challenges - Benefits

• Focus available resources on more urgent matters.
• The industry has been downsized.
• Evaluations, maintenance, etc. should not be
  mandated based on small increases in performance
  based solely on test data, unless there is a
  valid concern supported by additional data (more
  tests, vibration data).

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CPT Challenges - Benefits

• Increased safety system availability.
• If the upper limit is exceeded, the pump is
  inoperable.
• It cannot be returned to service unless
  maintenance is conducted or the condition is
  evaluated.
• New reference values must be established if an
  evaluation is used to return a pump to an
  operable status.
• New reference values established at a higher
  value may not be the best long term solution, if
  the test result is not typical of normal
  performance and is not supported by additional
  data.

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CPT Challenges - Conclusion

• The Code should be used as a tool to
• Determine and assess overall pump health.
• Trend performance and take actions prior to
  failure.
• Ensure operational readiness and provide one of
  the key inputs necessary to determine
  operability.
• A quarterly test conducted at or near design flow
  accomplishes these objectives.
• Also, a full flow test conducted 8 times over a
  two year period compared to one time in a two
  year period is far more effective in evaluating
  overall pump health, provides better trend
  capability, and provides more frequent assurance
  of meeting design requirements.

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CPT Challenges - Conclusion

• The Code should not
• Place unwarranted burden upon the utility.
• This was one of the stated objectives when
  developing the CPT.
• If your Group A tests are being conducted at
  design flow rates, then the additional
  comprehensive test may be considered a burden.
• Bring acceptable test results into question.
• A Group A test that passes at 104 of the
  allowable limit will result in questions relative
  to operability.
• When compared to the CPT limit.
• This tends to lead to passionate debates and is
  very difficult to defend.
• It is also difficult to tell management that the
  pump may have to undergo maintenance to ensure
  that it passes the next scheduled test.

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CPT Challenges - Conclusion

• QUESTIONS?