CHEVRON Compressors - Inspection and Testing

600 Inspection and Testing

AbstractThis section contains information on the purpose of and general principals for inspecting and testing compressors. It covers several quality-control tests, giving general guidance on when the respective tests may be cost-effective and appropriate.

Contents Page

610 General Comments 600-2

620 Non-Witnessed, Witnessed, and Observed Tests 600-2

630 Centrifugal Compressor Inspections 600-3

640 Centrifugal Compressor Tests 600-5

641 Four-Hour Mechanical Test

642 Assembled Compressor Gas Leakage Test

643 Performance Test

644 Complete-Unit Test

645 Full-load, Full-pressure, Full-speed Test

646 Other Tests

650 Reciprocating Compressor Inspections 600-13

660 Reciprocating Compressor Tests 600-15

661 Mechanical Running Tests

662 Bar-over Test

Chevron Corporation 600-1 December 1998

600 Inspection and Testing Compressor Manual

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610 General CommentsInspection at the point of manufacture is normally done by the CRTC Quality Assurance (QA) Team, or by a qualified inspector who is contracted for the work by the QA Team. The purpose of shop inspection is to obtain reasonable assurance that the equipment meets specification and order requirements, displays good workman-ship, and is free of significant defects or damage before it ships.

Inspection is warranted for all process gas compressors. Inspection coverage may also involve a Company machinery engineer and/or a mechanical specialist from the customer’s maintenance organization. Coverage should be agreed upon as earpossible and communicated to the vendor. Typically, the machinery engineer ormechanical specialist would always witness mechanical run or performance teslarge machines, and one of them might also witness:

• Final rotor balancing (centrifugals)• Final assembly• Dismantling after mechanical or performance testing and reassembly• Operational and cleanliness tests on lube and seal oil systems

620 Non-Witnessed, Witnessed, and Observed TestsInspection and testing of a compressor or parts of a compressor by the manufaturer may be “non-witnessed”, “witnessed”, or “observed”.

Non-Witnessed. This means that the manufacturer does the required test and certi-fies the results; the test results are reviewed by the Purchaser’s inspector during other inspection visits. Production is not stopped as it is for “witnessed” tests.

Witnessed. This means that a hold is applied to the production schedule and thecarried out with the Purchaser's inspector present. This may result in a double The vendor will include in his bid a cost extra for witnessing a test.

Observed. This means that the Purchaser requires notification of the test's timinHowever, the test is performed as scheduled, and if the Purchaser's inspector ipresent, the vendor may proceed with the test. A hold is not placed in the prodution schedule. Since only one test is scheduled, the Purchaser's inspector can to be in the factory longer than for a witnessed test, while set up is completed odebugging test equipment is done. The vendor will include a cost extra for observing a test that is less than the cost for witnessing a test.

The differential cost between observed and witnessed tests can be more than oby increased inspector's time for observed tests; observed tests may also be mbecause of insufficient advance notification by the vendor. Specifying an observtest is therefore not recommended.

If a test is important enough to warrant the presence of an inspector or engineewitnessed test should be specified. When a test is to be witnessed, it must be son the compressor data sheet or elsewhere in the order documents.

December 1998 600-2 Chevron Corporation

Compressor Manual 600 Inspection and Testing

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630 Centrifugal Compressor InspectionsThe principal inspection points are listed below in the normal manufacturing sequence. The cost of testing is usually added to the purchase cost in a compressor quotation.

1. Pre-Inspection Meeting. Held to review specifications and order requirements at the point of manufacture to verify there will be compliance. This visit should always be made at the compressor manufacturer’s plant and normally at the manufacturing plants for:

– Lube- and seal-oil consoles– Overhead seal oil tank (pressure vessel)– Gear (speed changer)– Driver (prime mover)

The Pre-inspection meetings will help resolve ambiguities that may delay fishipment or result in equipment that is not what the user specified. They alverify that manufacturers understand our inspection and testing requiremenand are aware of the required witness points. These meetings should be heall except small utility compressors.

2. Review of Compressor-Casing Fabrication Drawings (by Purchaser’s inspector prior to start of fabrication). This visit should always be made for compressors with fabricated casings. The casings are pressure containing but compressor manufacturers may use joint designs and materials that domeet normal minimum requirements for pressure vessels or pressure pipin(required by API 617).

3. Visual Inspection of Fabricated or Cast Casings Before Machining. This visit should always be made for fabricated casings, even when sound joint designs are on the fabrication drawings. Actual weldments frequently havemajor flaws that can be found visually; weld repairs must be made before machining since some distortion from welding is inevitable. Cast casings should be visually examined prior to machining to verify that they do not hasignificant visible defects.

4. Non-Destructive Examination of Fabricated or Cast Casings (liquid pene-trant, magnetic particle, ultrasonic, radiographic). Company compressor specifications will usually require some degree of NDE in addition to visualexamination and a successful hydrostatic test. Supplementary NDE beyondcontained in the specification should not be added unless it is clearly justifieby the service conditions, material characteristics, or established specificatrequirements. A materials engineer, QA engineer, or both should be consulsupplementary NDE is being considered for other reasons. NDE in itself is frequently inexpensive; it is the resulting repairs to upgrade castings which have been subjected to NDE that can be very expensive. When some form of supplementary NDE is specified, an acceptance standard must always be fied as well. Whenever NDE is specified, it should always be witnessed (ra



graphs interpreted when radiography is specified) and should be identified as a witness point on the compressor data sheet. (See Section 620 for definitions.)

5. Visual Inspection of Welded Baseplates Before Machining. This visit should always be made for large, or critical compressor baseplates. Weld quality and inadequate weld size have been problems on large baseplates.

6. Hydrostatic Test. A casing hydrostatic test is always performed. Witnessing the test is always warranted. Helium testing, if specified, should also be witnessed. (See item 4, Section 650.)

7. Visual Inspection of Welded or Cast Impellers Before Heat Treatment and Machining. This is warranted in most cases. Welding the impellers is difficult. The customer does not specify a quality standard, and the compressor manufac-turer will not be likely to initiate weld repairs on completed impellers since another round of heat treatment and machining would be required. Cast compressor impellers frequently have significant defects but the compressor manufacturer may be inclined to use them anyway.

8. Overspeed Test and Subsequent NDE of Impellers. Both should always be witnessed to check for cracks and distortion. Impellers are made from high-strength alloys and often have hub stresses close to the material yield point.

9. Stacking and Incremental Balancing of Rotor. This is usually not witnessed. It can require days of inspector time since the rotor is balanced several times during the course of assembly. If witnessing incremental balancing is being considered, consult a machinery specialist.

10. Final Balancing of Rotor. This should normally be witnessed along with dial indicator measurement of runouts at bearing journals, thrust bearing faces, and all points along the rotor with close clearances. Impeller wobble caused by warpage during weld repair is also checked at this time.

11. Runout Checks for Proximity Probes. This should be done before the compressor is assembled and should be witnessed. Its purpose is to verify that mechanical and electrical runouts of the rotor surfaces are low enough for the vibration monitoring system to operate satisfactorily without electronic compensation. (See the General Machinery Manual for additional information.)

12. Final Assembly of Compressor. This should usually be witnessed to verify internal clearances are correct, parts do not have significant visible flaws, and internal damage is not done during assembly. This will require a resident inspector for one week or more.

13. Mechanical Run and Performance Tests. One of these is usually specified to verify that the compressor is mechanically sound and to prove it will meet performance requirements. A mechanical test is often required by the manufac-turer’s own internal specifications. These tests should always be witnessed by a machinery engineer or mechanical specialist.

14. Dismantling After Test. As a minimum the bearings and seals are removed and inspected when the mechanical run or performance test is completed.



Inspection is done by the machinery engineer or mechanical specialist who witnessed the mechanical run or performance test.

15. String Test of All Job Equipment. A string test is a mechanical running (and sometimes performance) test of all the ordered equipment assembled together on the job baseplates to make sure everything operates satisfactorily. Consult a machinery specialist if a string test is being considered. A string test should always be witnessed.

16. Final Inspection. This is always done after compressor, driver, piping, and instrumentation are installed on the baseplate, but before painting is finished. Final inspection includes but is not limited to:

a. Review of equipment against specifications and data sheets line by line.

b. Dimensional check against reviewed outline drawings.

c. Verification that all required piping and appurtenances are present.

d. Visual inspection for defects or damage.

The following are inspection points for auxiliary equipment and drivers.

17. Drivers. (See the Driver Manual.)

18. Gears. Degree of testing and inspection will vary with speed and load carrying requirements. The following are usually witnessed.

a. Gear contact and backlash check in contact-checking stand.

b. Gear contact and backlash check in casing.

c. Mechanical run test (unloaded or loaded) if run test is specified.

19. Overhead Seal Oil Tanks. Checked for a high degree of internal cleanliness. (Also see the Pressure Vessel Manual for information on inspection of vessels.)

20. Lube and Seal Oil Consoles. The following are usually witness points:

a. Visual inspection of components prior to assembly for weld quality and cleanliness.

b. Pressure tests of completed systems.

c. Operational and cleanliness tests per API 614.

d. Final inspection before finish painting.

640 Centrifugal Compressor TestsNote This is a lengthy section. Nevertheless, these are typically expensive machines that are critical to large process plants, and they warrant considerable attention.



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641 Four-Hour Mechanical TestThe four-hour mechanical spin test is a standard test for most vendors. It is also specified in API 617 and in Company Specification CMP-MS-1876. The purpose of this test is to:

1. Check the vibratory behavior of the rotor-bearing system during acceleration and at maximum continuous speed.

2. Check for proper assembly and running clearances.

3. Prove that the bearings and seals operate satisfactorily under running conditions.

This test is considered to be strictly “mechanical.” No part of the aerodynamic performance of the compressor is measured during the test. The test is usuallyconducted with the compressor operating in a closed piping loop at a relatively pressure (100-200 psi discharge is common). An open piping loop could also bused. Although tests with the rotor running in a vacuum in its casing are sometiproposed, the Company's Specification CMP-MS-1876 prohibits the practice oftesting without flow through the casing. Vacuum-type tests are disallowed beca

1. The lack of significant gas density inside the casing can have an influence rotor dynamics.

2. The casing heats up abnormally from the churning of residual gas in casing(vacuum is not perfect).

3. The operation of oil-film type seals cannot be tested concurrently with the vacuum-type spin test.

For “flexible” rotors (those operating above the first critical), the location of the fcritical speed is verified during acceleration and/or deceleration when possible.the rotor system is highly damped, and if the rotor is dynamically balanced to aextremely low level of residual unbalance, it is not always possible to discern thfirst critical speed from plots of X or Y filtered vibration amplitude versus speedPlots of phase angle versus speed also may not provide a reliable indication offrequency of the first critical for the same reasons. For these rare occasions, thvendor's calculations are usually relied on for the location of the first critical. If other unusual phenomena were observed during the test, it might be advisabledeliberately unbalance the rotor or coupling to make the critical more distinguisable. Engineering judgment must be employed in such cases, and it is stronglysuggested that a mechanical specialist be consulted.

The inner seal leakage of the contract oil-film seals should be measured duringfour-hour spin test. As pointed out in API 617, it may not be possible to use thecontract outer seal bushing(s) during the test if the pressure in the test loop is tlow to cause an adequate oil flow rate through these bushing(s). In this case, stest bushing(s) with greater clearance is used. The inner seal ring, however, shhave proper differential pressure such that the inner seal leakage may be evaluCMP-MS-1876 includes some acceptance limits, the principal one being that on



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seal cannot have a leakage rate greater than 70% of the combined leakage of both seals.

642 Assembled Compressor Gas Leakage TestThis test comes after the four-hour spin test, and is conducted at maximum seal design pressure (usually settling-out pressure) at zero speed with the seal system operating. The purpose is to check for gas leaks at all joints and connections. Also, the test is applied to compressors handling hazardous or flammable gases. If the compressor has oil film seals, it is a good idea to have the seal oil leakage rate measured in this static condition, because this condition will often exist at the compressor installation during startups and shutdowns. The static leakage rate will be somewhat higher than that when the rotor is turning since the inner seal ring could be in an eccentric position (leakage varies approximately with the square of eccentricity). Very high static leakage could indicate an O-ring problem or some other fault that might not be apparent when the shaft is rotating.

If during the four-hour spin test, the seal oil leakage rate was not measured, or if the complete contract seal assemblies (both inner and outer rings) were not installed, a low-speed seal leakage test should be conducted at maximum seal design pressure. The complete contract shaft seals should be used, and the rotating speed should be at least 1000 RPM. This test will provide more meaningful seal leakage rates than those that can be obtained using non-contract outer seal rings. In fact, the low-speed leakage test should be the acceptance test. It is often not possible to spin the machine faster than 1000 RPM for this test because of test stand power or discharge temperature limitations.

Alternatively the seal leakage can be measured during the full-pressure, full-speed test if this optional test is specified.

643 Performance TestThe aerodynamic performance of a stage, of a section, or of a complete casing can be evaluated with an optional test using the procedures covered in the ASME Power Test Code (PTC-10, 1965), Compressors and Exhausters.

Aerodynamic performance refers to the shape of the head-versus-capacity character-istic curve. The ASME test is conducted to determine whether the compressor meets the quoted power and head at one operating point on the curve for one speed. This point is usually the normal operating point, but can be any other point as specified. The surge point is determined during the test, and at least four other points are taken along the speed line including one at a capacity beyond that of the point in ques-tion. Specification CMP-MS-1876 calls for additional points to be taken for vari-able speed machines. These additional points result in a higher cost for the performance test, but experience has shown that the added cost is justified.

Acceptance criteria are given in API 617 and CMP-MS-1876. Note that some vendors use the term “head rise-to-surge (head RTS),” and that this term is notnumerically equal to “pressure RTS.” RTS is an important factor as it can have



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major influence on the operating stability of the machine, and on the design of the anti-surge system. RTS tends to become a problem with gases that are heavier than air and have relatively low acoustic velocities. Propane and propylene are examples of gases that can have a very flat characteristic from the normal operating point to the surge point. Accordingly, a small change in the system resistance would effect a major change in capacity causing a potentially unstable situation. CMP-MS-1876 requires a guarantee on the RTS quoted by the vendor.

There are three classes of ASME loop tests as follows:

Class I TestsThe test gas used is the same as the actual gas specified. The pressures are essen-tially the same as those specified. In general, this class of test can be applied only to air compressors with an atmospheric suction for strict conformance to the ASME code. The test piping would be an open loop with an atmospheric inlet and the discharge vented to atmosphere downstream of a control valve. The test conditions of Class I tests more closely duplicate actual operating conditions than do the test conditions used in the other two classes of ASME tests. Modified open-loop Class I tests that do not meet the Code are sometimes run to quickly approximate the performance.

Class II TestsThe test gas is different than the specified gas, and in the reduction of test data it is assumed that the test gas and the specified gas behave in accordance with perfect gas laws. The test piping is a closed loop.

Class III TestsThis test is the same as Class II except that compressibility factors are applied along with changes in “k” value from suction to discharge.

In Class II and III tests, the test speed and test pressures and temperatures aregreatly different than the specified values. The ASME code includes tables shothe allowable deviations for volume reduction, Q/N, machine Mach number, andmachine Reynolds number for Class II and III tests. Similarly, permissible depature from specified conditions for Class I tests are listed including pressure, tematures, specific gravity of the gas, speed, and capacity. See Figure 600-1.

Class II tests are seldom used for compressors in the petroleum industry. Classtests are the most common. Test gases for Class III tests include carbon dioxidnitrogen, Refrigerant 12 or 22, and mixtures of helium and nitrogen. Generally, preferred to run the test with a pure unmixed gas. With a mixture of helium andnitrogen, it is sometimes difficult to maintain a constant gas composition for theduration of the test. If makeup is required in the loop during the test, it is not eaadd the correct proportions of the two gases. In such cases, it may be advisablrequire the compressor vendor buy an adequate quantity of certified pre-mixedfrom a specialty gas manufacturer.

Some Class III tests are run with a sub-atmospheric suction to reduce power rements during the test. This procedure invites air leakage into the loop which wil



upset the gas composition. Therefore, flange tightness should be carefully checked prior to test startup.

Figure 600-1 shows some typical test gases used for various specified gases in Class III closed-loop tests. In general, the heavier test gases are used for heavy specified gases. Helium/nitrogen mixtures are used for hydrogen-rich gases such as ammonia synthesis and refinery recycle gases.

Note that the equivalent speed, capacity-speed ratio, and volume ratio, at which a Class III test is run, are generally compromises between the various departures allowed by the PTC-10 code (see Figure 600-2). CMP-MS-1876 requires that the test speed has a safe margin from the rotor’s critical speed.

The subject of Reynold’s Number corrections of the results usually comes up when the performance test agenda is being developed by the vendor and purchaser. The corrections suggested by ASME PTC-10 have been proven to be very misleading, and are inclined to favor the vendor. Depending on conditions, the ASME correc-tions could allow a specious improvement in efficiency of 6% or more. Most purchasers have disallowed any correction, and some vendors voluntarily decline to make corrections. In some special cases, 50% of the corrections would be allowed.

The effects of flow in different regimes of Reynolds Number is well known, and some correction should logically be applied. The problem is in developing suitable correlations of the complex flow path in the compressor.

In the early 1980’s, a group of eight major compressor manufacturers in the United States and Europe got together under the auspices of the International Compressor and Allied Machinery Committee (ICAAMC) to develop a new correction method. Test data were pooled, and good correlations between measurements and predic-tions were established. The ICAAMC method includes the friction factor concept that is used in the analysis of flow in piping. The method has been proposed to ASME for possible adoption in the next revision of the PTC-10 Code. It has already been used successfully on several compressors. The ICAAMC method should be considered for cases where the ratio of Reynolds Numbers for test and specified conditions are in the range of 0.01 to 100.

Modified closed-loop Class I tests have been run on high-pressure machines with discharge pressures ranging from about 3000 to over 9000 psi. Such machines are used for injection of natural gas into an oil field formation. For these tests, the test gas is formulated by blending several hydrocarbon gases and other gases to closely approximate the composition of the actual gas. The test is run at full pressure and full load. Sometimes the main objective of such a test is to determine mechanical behavior at high-pressure levels, and aerodynamic performance may be of secondary importance. A Class III test is usually run in addition to the modified Class I test. The full pressure test along with the Class III test will provide good data for predicting gas properties.

Performance tests are ordinarily specified for all machines in critical service where the process flow and pressure is crucial, or where the service is troublesome and unpredictable such as gas injection. If some components of the machine are


600 Inspection and TestingCom

pressor Manual

December 1998

600-10Chevron Corporation

Fig. 600-1 Typical Test Gases and Equivalence Values (Courtesy of the Elliot Company)


Fig. 600-2 Allowable Departures From Specified Design Parameters ASME PTC-10 (1965) Test (From ASME PTC-10 (1965). Courtesy of the ASME)



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unavoidably unproven, the machine should have a performance test. The perfor-mance test will often shake out mechanical problems.

The performance test is generally good insurance for machines in tough duty, since it is far less expensive and time consuming to modify a machine at the factory than at the jobsite.

When it is decided that a performance test is required, merely specifying an ASME test is seldom sufficient to obtain the desired results. The objective of the tests should be stated in order that the vendor and purchaser can work out an appropriate test procedure. In this regard, consultation with a mechanical specialist is strongly recommended.

644 Complete-Unit TestThe complete-unit test is also called a “String” test. It consists of coupling up alcomponents and auxiliaries of a compressor train, and running them together inmechanical spin test. This test is strictly mechanical, and can be performed in pof or in addition to separate mechanical tests of individual components. The purof the test is to confirm the mechanical compatibility of the components and auries. The auxiliaries can include the contract couplings, the lube and seal oil system(s), and the basic instrument and control systems. If the compressor traincludes a gearbox, the test agenda may include torsional vibration measuremeverify the vendor's analysis.

Sometimes it is impossible to test the actual driver with the rest of the componeowing to its size or lack of power or fuel in the shop. In this case a shop driver mbe used. Although this test is not as informative as a complete string test, it stillmerit when the compressor train is complex.

645 Full-load, Full-pressure, Full-speed TestA full-load, full-pressure, full-speed (FLFPFS) test is often called for when the compressor train is in gas injection service or other services where the dischargpressure exceeds 2000 or 3000 psi. There is no hard-and-fast rule for the preslevel at which such a test should be specified. Much depends on the Companythe vendor's experience. A compressor handling natural gas at a discharge preof 4000 psi should undergo a FLFPFS test. As mentioned previously in regard performance tests, such a machine would also be a likely candidate for a modifASME Class I test to be run concurrently with the FLFPFS test.

A FLFPFS test for a compressor delivering a hydrogen-rich gas at 3000 psi proably would not be justifiable. The appropriateness of the FLFPFS test is relatedthe density of the gas in the compressor casing. Extremely dense gases can caexcitation of the rotor resulting in destructive levels of sub-synchronous vibratioThe high pressure level in the casing can cause the oil film seals to partially actbearings resulting in a shorter effective length of the rotor. Thus, the frequency the sub-synchronous vibration is usually higher than that of the first critical speebut lower than the frequency of running speed. Sub-synchronous vibration has



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This sub-synchronous phenomenon is known as aerodynamic whirl, and is too complex to adequately cover in this manual. When high-pressure centrifugal compressor applications arise, it is recommended that a mechanical specialist become involved in the specifications for the machinery as well as for the testing.

646 Other TestsThe helium test, sound-level test, auxiliary-equipment test, and other optional tests listed in API 617 are self-explanatory. Refer to CMP-MS-1876 for other requirements.

650 Reciprocating Compressor Inspections1. Pre-Inspection Meeting. Held to review specifications and order requirements

at the point of manufacture to verify there will be compliance. This visit should always be made at the compressor manufacturer’s plant and normally at the manufacturing plants for:

– Lube-Oil System– Pulsation Dampers (pressure vessels)– Gear (speed changer)– Driver (prime mover)

The Pre-Inspection meetings will help resolve ambiguities that may delay fishipment or result in equipment that is not what the user specified; Pre-Instion meetings also verify that manufacturers understand our inspection andtesting requirements and are aware of the required witness points. These mings should be held for all except small utility compressors.

2. Non-Destructive Examination of Cylinders (liquid penetrant, magnetic particle, ultrasonic, radiographic). Cylinders are normally accepted on the basis of visual examination and successful hydrostatic tests. SupplementarNDE should not be added unless it is clearly justified by the service conditimaterial characteristics, or established specification requirements. A materengineer, QA engineer, or both should be consulted if supplementary NDE being considered for other reasons. NDE in itself is frequently inexpensive;it is the resulting repairs to upgrade castings which have been subjected to NDE that can be very expensive. When some form of supplementary NDE isspecified, an acceptance standard must always be specified as well. Whenis specified, it should always be witnessed (radiographs interpreted when radography is specified) and should be identified as a witness point on the compressor data sheet. (See Section 620 for definitions.)

3. Hydrostatic Tests. Cylinder hydrostatic tests are always performed and shoualways be witnessed. The purposes of the hydrostatic test are to prove thetural integrity of the cylinder, to reveal leaks caused by material flaws that



extend through the cylinder wall, and to reveal leaks caused by machining errors or damage to machined surfaces. The gas side of the cylinder and cylinder heads are tested separately from the cooling water side to verify there is no leakage from one side to the other.

4. Helium or Air Pressure Test. API 618 or the job specification may require helium or air pressure tests in addition to the hydrostatic tests. Gas tests are more likely to find small leaks than hydrostatic tests; gas tests are made with the cylinder submerged in water (a helium probe is sometimes used for helium tests instead of submergence). Since compressed gas has a great deal of stored energy, high-pressure gas tests should always be preceded by a successful hydrostatic test for safety. When a helium or air test is required, it should always be witnessed.

5. Compressor Valve Leak Test. This test measures the amount of time for a fixed volume of gas behind a valve to drop from one defined pressure to another. Special fixtures are required for this test which is sometimes specified for all of the compressor valves. If the test is required, it should be witnessed.

6. Alignment of Cylinders to Frame. Concentric and axial alignment of frame, crosshead guide, distance piece, and cylinder are carefully measured. Witnessing the alignment check should be considered for large machines; consult a machinery engineer to determine if it is warranted. Note that if these alignments are not done correctly in the shop, then field alignment will be much more difficult. Although the vendor would still be liable, getting them to take care of it could be very troublesome. Manufacturers will usually resist fitting the distance pieces and cylinders on large units.

7. Piston Rod Runout and Piston/Head Clearance. These measurements on the assembled compressor provide assurance that cylinder alignment is satisfac-tory, machining/assembly of crosshead/piston rod/piston are correct, and that the manufacturer’s specified head clearance is in fact present. These measure-ments should always be witnessed. Dimensional check of the compressor against the outline drawing, and visual inspection for defects and damage are done at this time. These steps would also be difficult in the field, as would getting the vendor to correct any problems. The vendor might claim some external factors.

8. Mechanical Run Test. This test is usually run without pressure-loading the cylinders to verify that the compressor is mechanically sound. Cylinder heads are removed after the test for inspection of the cylinder liners. This test (and post-test inspection) should always be witnessed. For very large compressors, manufacturers do not have the facilities to make mechanical run tests.

9. Final Inspection. This may not be required if the compressor is shipped disas-sembled as many are. For compressors that ship assembled, final inspection is similar to item 16, Section 630.

The following are inspection points for auxiliary equipment and drivers.

10. Drivers. (See the Driver Manual)



11. Gears. (See item 18, Section 630)

12. Pulsation Dampers. (See the Pressure Vessel Manual). Checks are made for:

a. A high degree of internal cleanliness and adequate preservation of cleanliness.

b. Flange faces being in the same plane for nozzles in a single bottle that connect to two separate cylinders.

13. Lube-Oil System. (See item 20, Section 630)

660 Reciprocating Compressor Tests

661 Mechanical Running TestsAPI 618 reciprocating compressors are almost never run at full speed in the factory. Packaged and skid-mounted units are sometimes run unloaded at the compressor factory or at the packager’s shop. Alarms, shutdowns, gages, lube systems, and overspeeds may be functionally tested at this time to avoid problems in the field. This test is described in API 618. Shops often lack power or fuel to conduct such tests. The mechanical running test is not as meaningful for the reciprocating machine as it is for the centrifugal compressor. Although the running test would check mechanical compatibility and the workability and heat loads of the lube system, generally the test is not cost-effective.

Class B machines going offshore tend to be considered for mechanical testing more often, but again the test facilities may limit the sizes of machines and types of drivers that can be tested. Mechanical testing of Class B machines is still not a common occurrence.

Because of their smaller size and rating, Class C and D compressors can be given a mechanical running test more easily. For the same reason, such a test may be more difficult to justify unless the service is semi-critical or offshore.

The vendors should be consulted regarding their testing capability before speci-fying a mechanical running test for reciprocating machines.

662 Bar-over TestThe bar-over test is usually a manufacturer’s standard test. Its purpose is to check the end clearances of the pistons, and to measure the cold vertical and horizontal piston rod runout. A complete description of rod runout is included in the Appendix of API 618.


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CHEVRON Compressors - Inspection and Testing