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The prime intent of witness testing is rarely just to see the equipment operate when the start button is pushed. Witness testing provides the opportunity for an engineer or quality inspector witnessing the test (hereinafter, called the "witness") to ensure that the equipment vendor carries out the factory acceptance tests in accordance with the specifications and other contract requirements. Many a time, the size and complexity of the equipment may not be palpable through drawings and documentation.
This is an excerpt from the paper, “Witness testing of API 610 centrifugal pumps and API 611 steam turbines” by "Nick" Ganatra of FMC Technologies, Inc. and R. C. Patel, a consulting engineer, presented at the 2012 Pump Symposium.
Witness testing also provides the opportunity to experience the "look and feel" of the actual equipment. Furthermore, it provides the opportunity to identify and address issues with non-conformance or misinterpretation of the specifications with respect to equipment construction or testing. The following is just an abridged list of such items:
• Location/orientation of connections, equipment, instrumentation and accessories • Instrumentation, controls and their tagging
• Nameplates and equipment tagging
• Scope of supply of equipment, instrumentation and accessories
• Painting and coating requirements The cost of correcting equipment non-conformance significantly increases for both, the vendor and the purchaser, once the equipment is shipped to the field.
Hence, it is in the best interests of both these parties to identify non-conformances in the vendor's factory and ensure compliance with the contract requirements before shipment. It is important to note that factory acceptance testing is generally performed prior to the final painting, assembly and packaging of equipment. Hence, certain items that are listed above may still not be evident during testing. However, if the purchaser has multiple equipment orders with the same vendor, then the witness can request to see the other equipment that has already passed testing and is being assembled and packaged for final shipment. In the same manner, the witness can request to look at the other items on order that are being manufactured at that time.
During the same trip for test witnessing, the witness can request the vendor to give them a tour of the manufacturing facility. Witness testing is generally also specified if the purchaser is uncertain about the vendors' abilities, experience and performance. Moreover, for new equipment designs and for prototype qualification testing, witness testing provides the opportunity to ensure that the agreed test procedures are unequivocally followed.
Finally, witness testing may also be required to ensure satisfactory operation with certain critical constraints such as insufficient NPSH margin, high energy density or high operating temperature. When possible, the test to be witnessed should not be the first one seen by the witness at that facility. It is recommended that an apprentice type system be used – experienced engineers should recommend to management that they take along a new engineer for each new type of test or facility. Having stated the above, one cannot negate the fact that the requirement of witness testing adds the burden of cost, time and resources to the project.
Hence, the decision to require witness tests for certain equipment should be made prior to sending requests for quotation with careful consideration to the size, criticality and complexity of the equipment, in addition to the purchaser's past experience with the vendor(s). The purchaser should be mindful of the fact that once an order is placed, it usually becomes hard to justify the addition of witness testing at a later stage of the project.
Virtual witnessing is a fairly recent development that allows an engineer or inspector to witness equipment testing from the comfort of their work location. Measured parameters and collected data can be displayed on the witness' computer in real time during the testing. Generally, test performance curves can also be constantly seen by the virtual witness on their computer screen as the test progresses. In addition, multiple cameras are often installed at the test site, thus enabling the virtual witness to remotely monitor the actions and events at the test site from their computer screen.
To enable such witnessing, the vendor provides the witness with access to a secure internet location that has a dedicated username and password. From there, the witness can launch a secure application that is configured to enable such witnessing. Although the significant benefits of virtual witnessing with respect to cost, time and resources are obvious, it generally limits the extent of witness' involvement in the testing. Moreover, the witness' potential to uncover other problems with equipment non-conformance is also fairly reduced.
Virtual witnessing typically limits itself in scope to the contract performance tolerances and vibration limits for specific subsystems (e.g. hydraulics, bearing housing, shaft). On the other hand, the witness' physical presence can ensure satisfactory operation of the equipment as a complete unit, wherein problems not explicitly spelt out in the test acceptance criteria may also be uncovered. Hence, when possible, physical witnessing of tests should be generally preferred to virtual witnessing.