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Commissioning and Qualification 335
design or coverage testing. Their solution for unsatisfactory coverage test results
was to increase the CIP flow rate (often significantly).
When ProjectAC&Q planning was initiated, the discrepancy between design
flow assumptions and coverage testing results became apparent. Equipment and
piping werealready installed. Aproblem with supply and return pump sizing was
suspected and their operating capabilities were checked. The engineer checked the
supply pump sizing based on the circuits with the highest anticipated flow rates
and recommended larger impellers and motors (which we changed). In anticipation
of undersized return piping, adrain step was added within the NDS to keep the
process tank liquid levels low (if necessary). Later other related issues were
discovered:
1. The worst case for CIP supply pump sizing needs was actually low flow, high
head circuits. This resulted in further pump upsizing.
2. The combination of the CIP tank size and freshwater supply design rate would
not allow us to perform once-through rinses at the higher CIP flow rate without
running out of water. This was areal cycle time issue.
3. For Project B, the capacity was increased for the water supply loop, but the CIP
tank vent was too small for the higher fill rates.
Allowing the flow rates through the spray balls to be increased significantly
above the design basis was amistake. In retrospect we should have
1. initially had the spray balls designed and fabricated by someone with the
proper experience;
2. had the spray ball designers present during coverage testing for
necessary modifications;
3. had abetter documented design basis; and
4. replaced the spray balls as per number 1above.
Coverage testing performed at the factory does not necessarily eliminate
the need for coverage testing on site with the actual CIP system. Effectiveness of the
coverage testing can be affected by:
1. Flow rate or spray ball supply pressure
2. Contact time
3. Pulsing sequence
4. Equipment configuration
It is important to document the conditions used for factory coverage testing. It
is difficult to duplicate at the factory all the conditions that will be present in your
plant. Repeat coverage testing at your site may be necessary.
FUNCTIONAL TESTING PLANNING
As you might expect, the complexity of functional testing grows as your system
complexity grows. Functional testing planning requires an in depth understanding
of the detailed design. As discussed before, knowledge of the design basis is crucial
to good planning and execution. Just as important is an understanding of the
software design.