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Comprehensive Pump Testing Challenges

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Title: 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.

3
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.

4
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.

5
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.

6
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.

7
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.

8
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.

9
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.

10
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?

11
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.

12
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.

13
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.

14
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.

15
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.

16
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.

17
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.

18
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.

19
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.

20
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.

21
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.

22
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.

23
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.

24
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.

25
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.

26
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!

27
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.

28
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.

29
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.

30
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.

31
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.

32
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.

33
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.

34
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).

35
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.

36
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.

37
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.

38
CPT Challenges - Conclusion
  • QUESTIONS?
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