Transcript Comprehensive Pump Testing Issues

Comprehensive Pump
Testing Challenges
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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

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Papers were presented at the second and third NRC/ASME symposiums, and a letter
was written by the NRC to the O&M 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.

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It was decided that there was an urgent need to develop a comprehensive pump test.

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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.
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
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Positives and Negatives associated with the CPT.
Positives

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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

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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
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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
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It is also important to point out that the pressure
instrument is the ONLY equipment change
This concept is commonly misunderstood.

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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
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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
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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:
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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
M&TE 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
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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.
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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
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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

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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
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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
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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
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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
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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.
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Does the improved pressure instrument accuracy provide better long
term trending capability?
In my opinion………
NO!
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CPT Challenges – Pressure
indication
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Here’s 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
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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 I&C 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

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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:

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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

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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

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The benefits associated with this proposal are many.
First and foremost:

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Better assessment of overall pump performance.
Better trend capability.
Improved ability to detect degradation.
Reduced capital costs.
 Accurate pressure gages are expensive.
Reduced O&M 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?
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