{"id":396,"date":"2010-08-01T21:03:31","date_gmt":"2010-08-01T21:03:31","guid":{"rendered":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/?p=396"},"modified":"2011-06-02T14:23:07","modified_gmt":"2011-06-02T19:23:07","slug":"important-aspects-of-centrifugal-compressor-testing-part-1","status":"publish","type":"post","link":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/2010\/08\/important-aspects-of-centrifugal-compressor-testing-part-1\/","title":{"rendered":"Important Aspects of Centrifugal Compressor Testing-Part 1"},"content":{"rendered":"

Every centrifugal compressor, whether it is new or has been in service for many years will most likely be tested to verify its thermodynamic performance.\u00a0 For a new machine the testing may be conducted in the manufacturer\u2019s facility under strict controlled conditions or in the field at actual operating conditions.\u00a0 Older compressors that have been placed in service after maintenance or have been operating for an extended period of time may require testing to verify the efficiency and normal operation.\u00a0 This TOTM will review ASME PTC-10 (also referred to as the Code) testing procedure and other topics that contribute to an accurate centrifugal compressor test results.<\/p>\n

This two-part series will review the salient aspects of a performance test.\u00a0 Part 1 will review the thermodynamic performance test objectives established in the Code as well as other factors to consider in a testing procedure.\u00a0 While this code is primarily applicable to shop testing it can also apply to field testing.\u00a0 Part 2 will review the Code assumptions and basic performance relationships.\u00a0 It will also examine the three important principles that influence the operating conditions and ultimately influence the accuracy of the performance test.\u00a0 They are volume ratio, Machine Mach Number and Machine Reynolds Number.<\/p>\n

Introduction<\/strong><\/p>\n

The purpose of a performance test is to verify that a centrifugal compressor will perform in accordance with the manufacturer\u2019s design at the operating conditions given in the specifications.\u00a0 It also provides a method of confirming the shape of the compressor head-flow curve, efficiency, and the maximum and minimum flow limits at various speeds.\u00a0 Frequently a performance test is conducted under field conditions with the specified gas and operating conditions.\u00a0 However, if the performance test is conducted in the shop it may not be possible to test the compressor with the specified gas because of safety concerns or testing facility limitations.\u00a0 Whether the test is conducted in the field or in the shop, proof of the compressor design is recommended and often necessary to demonstrate contractual obligations and mechanical integrity.<\/p>\n

Frequently the gas composition used to confirm a compressor performance differs from the specified gas.\u00a0 This is often the case regardless if the test is conducted in the field or in the shop.\u00a0 For field tests, where the gas composition and operating conditions are set by the process, adjustments must be made in the calculations to confirm the compressor design specifications.\u00a0 Typically, a shop test is conducted with a carefully selected mixture of gases blended together to form a gas that has physical properties that closely resemble the specified gas.\u00a0 Even with a substitute gas, differences remain which influence the test results.<\/p>\n

The original compressor design places limits on the thermodynamic performance.\u00a0 The most important of these limits include flow rate, power, temperature, pressure and speed.\u00a0 There are other design restraints which are not as commonly known but will also influence the compressor performance.\u00a0 Such factors are volume ratio, Mach number and Reynolds number.\u00a0 These limits were incorporated in the compressor design and are influenced by gas properties, operating conditions and the mechanical design.\u00a0 To verify the design and operating limits for a compressor, it is necessary to test the machine.\u00a0 For new machines, these tests are commonly performed in the manufacturer\u2019s facility; however, the testing is sometimes performed in the field.\u00a0 It may also be helpful to periodically test a compressor to trend the machine performance.\u00a0 Testing conducted during commissioning will establish a baseline of performance.\u00a0 Periodic field tests are often conducted to verify the overall performance and signal changes that may predict mechanical damage, internal fouling, or other deteriorating conditions.<\/p>\n

Summary of ASME PTC-10 \u2013 Performance Test Code <\/strong>
\nThe procedure presented in the Code provides a method of verifying the thermodynamic performance of centrifugal and axial compressors.\u00a0 This code offers two types of tests which are based on the deviation between test and specified conditions.\u00a0 A detail procedure is given for calculating and correcting results for differences in gas properties and test conditions.\u00a0 The following briefly describes the guiding principles of the Code.<\/p>\n