WITNESS TESTING
Many companies affiliated with the petroleum, petrochemical and natural gas industries require at least some machinery testing to be witnessed by quality inspectors and/or engineers at the equipment vendor’s shop prior to release for shipment. This ensures that the testing is being performed in accordance with the contract requirements, applicable standards and/or test procedures that have been reviewed and accepted in advance of the test. Successful witnessing of these tests requires prior understanding of the test setup, test conditions and measured parameters.
THE RATIONALE OF WITNESS TESTING
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. 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
• Documentation
• 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.
TIPS ON WITNESS TESTING
Before the Test the witness should review the test procedure with regard to the contract specifications in advance for acceptability and become completely familiar with the testing methodology before traveling to the vendor's factory. Furthermore, the witness should become familiar with and carry copies of necessary supporting documents to the test. Examples of such helpful documents are given below:
• Contract specifications and technical datasheets
• Applicable industry standards
• Test procedure(s) • Piping and Instrumentation Diagrams (P&IDs)
• Equipment General Arrangement (GA) drawing(s)
• Applicable detail drawings
• Contact information of key project decision-makers and subject matter experts
After careful review of the contract documents, the witness should develop a checklist based on project specifications and referenced test standards (Jones et al., 2008). This checklist should have a list of items to be observed before, during and after the test, besides having provisions for recording readings from the test instrumentation in a tabular format. Table 1 of this tutorial is an excerpt of such a checklist.
