Screw Compressor Testing 

This article provides you sample Screw Compressor Testing and Inspection Procedure. This content also covers the Screw Compressor mechanical running test and performance test or what is named screw compressor factory acceptance test.

1. Screw Compressor Testing - General

1-1 Scope of Application

This document covers procedures and methods of tests, examinations and inspections to be performed to the Screw Compressor which has been manufactured and supplied by screw compressor vendors.

1-2 Purpose of Examination and lnspection

The purpose of the examinations and inspections mentioned herein is to control manufacturing process of the compressors, as well as to recognize accordance with the related specifications and the fulfillment of the designated function and safety.

Furthermore, these manufacturing examination/inspection records will be helpful in routine maintenance or in the event of machine troubles.

1-3 Method of Examination and Inspection

1-3-1 The examination and inspection shall be performed according to the specifications presented in purchase order approved inspection and test plan.

1-3-2 The examinations and inspections shall principally be carried out by the staffs of the quality control and assurance of screw compressor manufacture, and may be, if required, witnessed or observed by Purchaser, Client or appointed third-party inspection agent.

Such witness or observation in Screw Compressor Testing shall, in principle, be effected in a range not opposing or affecting manufacturing processes.

The term witnessed means that a hold shall be applied to the production schedule and that the inspection or test will be conducted with the purchaser or his agent in attendance.

The term observed means that the purchaser requires notification of the timing of the inspection or test.

The screw compressor testing or inspection is performed as scheduled, however, if the purchaser or his agent is not present the vendor can proceed to the next step.

1-3-3 Notifications to the witness tests shall be forwarded to the customer not less than 14 days in prior to the scheduled date of the shop tests. The one week period will be informed to the customer on 3 weeks in prior to the expected date of the mechanical running test.

1-4 Reports to be Submitted

1-4-1 After examinations and inspections, screw compressor testing records shall be submitted according to the inspection and test plan document. The test records shall include the following descriptions:

(1 ) Name Of Purchaser

(2) Job No., Item No., and Equipment Name

(3) Name of Manufacturer

(4) Date of Manufacture and Examination/Inspection

(5) Records of Tests And Examinations/Inspections

1-4-2 The Screw Compressor testing records shall be written in English language. Pipe sizes shall be indicated in inches.

2. Screw Compressor Testing - Tests and Inspections of Compressor

2-1 Genaeral

General description on examinations/inspections to be performed on the compressor proper and the related parts are mentioned in this chapter.

The inspection items of each major part are shown in inspection and test plan.

2-2 Material Inspection

2-2-1 As for the major parts, test pieces shall be sampled therefrom, and shall be subjected to various tests according to ASTM material or other pertinent standard. These tests may be substituted for mil sheets or material certificates of material suppliers.

2-2-2 Criteria

As per material specifications of ASTM, or other pertinent standards, if the material is based on the other standard.

2-3 Nondestructive Examination and Inspection

Parts of high importance should be subjected to non-destructive examinations and inspections.

The nondestructive examinations and inspections imply magnetic particle examinations.

Appropriate and practical examinations shall be employed therefrom and Carried out in accordance with approved NDE procedures.

2-3-1 Rotor & Shaft

The rotors shall be subjected to ultrasonic examination according to the approved procedure.

2-3-2 Casing

The compressor casing shall be subjected to magnetic particle examination for repair welded portions based of approved procedure.

Repairs and Repair Welds

The repair will be performed without Customer's approval except the below 'major' defect:

(1) It entails the removal of more than 50% of wall thickness.

(2) It extends over a length of more than 150mm in one or more directions.

(3) The total surface area of all repairs exceeds 10% o,f the original surface area.

All defects defined as above and proposed repair procedures shall be submitted to Customer for approval. Repair work shall not be started until approved by Customer.

2-4 Hydrostatic Test

2-4-1 The hydrostatic test pressure shall be, as a minimum, 1.5 times the maximum allowable working pressure with a tolerance of non-negative and plus 5%.

Painting shall not be performed until the hydrostatic and the air leak test have completed.

2-4-2 Fluid used for the hydrostatic test is industrial water. Max. chloride contents of the test water will be 250 ppm for carbon steel and 25 ppm for stainless steel.

2-4-3 For corrosive materials, rust inhibitor may be added to the test water.

2-4-4 The hydrostatic test shall admit neither leakage nor abnormal deformation.

2-4-5 The hydrostatic test pressure shall be held for a minimum of thirty (30) minutes while neither any leakage nor any other apparent defects are observed.

2-4-6 For parts which passed the hydrostatic tests, the test pressure and testing date shall be die-stamped.

2-5 Leak Test

2-5-1 The test pressure shall be the maximum allowable workin pressure. (-0, +5%)

Leak test shall be performed in casing chamber without mechanical seal. Leak test for mechanical seal will be performed individually.

2-5-2 The leak test shall be carried out in the following manner:

(1) Charge the portion so as to gradually increase the pressure to 50% of the test pressure.

Precautionary measures should be taken to protect personnel.

(2) Thereafter, increase the pressure in steps by approximately 10% of the test pressure until the required test pressure is reached.

(3) Hold it for minimum 30 minutes to inspect.

(4)Apply bubble solution to the casing generally.

2-5-3 The acceptance criterion for this leak test is no deformation and no leakage.

2-6 Pneumatic Test

As the silencers are internally packed with stainless steel wool and can not be readily dried, pneumatic test is used instead of the hydrostatic test. All inspection items required prior to pneumatic test shall be completed and confirmed.

Prior to testing, the equipment shall be thoroughly cleaned to be free from all dirt, weld spatter, loose scale, oil, paint and all other foreign matters.

Pressure retaining parts shall not be painted until the pneumatic test is completed.

The pneumatic test will be carried out in the following manner:

(1)The test shall be performed in accordance with ASME Sec. VIII, Div. 1, UG-100

(2) Pneumatic test with air or nitrogen shall be carried out by soap bubble method at 1.1 MAWP and held for at least 30 minutes.

(3) It shall be confirmed that the pressure vessels are free from any abnormalities such as local bulging or elongation, and leakage during the pneumatic test.

2-7 Balancing Test

2-7-1 Unbalance shall be corrected at the rotor end planes by means of a drilling machine or other appropriate means. (two-plane correction)

(a) The rotating elements shall be balanced in the following assembly by means of a dynamic balancing machine:

1) Timing Gear + Male Rotor + Coupling Hub

2) Timing Gear + Female Rotor

(b) Accessories to be mounted on the shafts such as thrust collars and etc. shall be installed.

2-7-2 Criteria

API 619 4th edition, 2004 ( provides that maximum balance shall be per grade G2.5 of ISO 1940/ANSI S2.19.

2-8 Dimensional Check

2-8-1 The dimensional check shall be based on the manufacturing drawings to ensure perfect fitness for assembling and servicing.

The following dimensional check records of the major parts necessary for installation, maintenance and alignment shall be submitted:

(1) External fit dimensions

(2) Relative dimensions necessary for assembly and maintenance

(3) Relative dimensions necessary for installation and alignment

(4) Terminating points

2-8-2 Criteria

As per dimension tolerances indicated on manufacturing drawings, and applicable standard.

2-9 Clearance Check

2-9-1 Compressor

The following clearances shall be measured to check on assembling the compressor:

  • Carbon rings
  • Journal bearings
  • Thrust bearing clearance
  • Timing gear backlash
  • Specified additional value for Casing-Rotor dischar end plane

2-9-2 Rotor clearance

(1) Rotor setting clearance ratio shall be measured.

(2) Inter-lobe clearances shall be measured.

2-10 Visual Check

The visual check shall be carried out under the self-check system from time to time in the course of manufacture from raw materials and processing of parts, to the final assembly.

(1) Compressor Casing

The visual check for the casing shall be carried out. No cracks or hot tears are permitted.

(2) The following shall be visually checked :

Welding bead and heat affected zone, if any.

Quality of finished parts.

Review of heat treatment records, if any.

(3) The number of furnished parts and fitting conditions shall be checked.

2-11 Screw Compressor Mechanical Running Test

2-11-1 General

The compressor shop running test will be performed by the procedures described herein.

The compressor will be tested with the inlet and discharge lines open to the atmosphere, using screw compressor manufacture shop test facilities including a speed-up gear, driver, shaft coupling, lube oil system and silencers etc. The test will be carried out at one point around the normal operating speed.

The contract bearings and the seals will be used during the shop running test, but the seal portion will be open to the atmosphere. The oil conditions will be so adjusted that they meet the normal operating values recommended by screw compressor manufacture.

The running test will be made in the following manner:

2-11-2 Running-in

The running-in will be carried out to confirm a safe start-up.

2-11-3 Heat Run

For a minimum of 30 minutes after running conditions have stabilized, the compressors will be operated at a specified discharge temperature.

2-11-4 Mechanical Run

After completion of the heat run, the compressor will be kept running for a minimum of four hours after running conditions have stabilized, while the mechanical performance is checked.

The pressure ratio will be as near to the normal operating conditions as possible whenever the discharge temperature limitation permits.

As for the Heat Run, the suction and discharge pressures shall be so adjusted that the discharge temperature will meet the specified value.

During the Mechanical Run and the Performance Check, the suction may be throttled to obtain as near as the specified pressure ratio.

Heat run temperature must be in sspecified value with specific tolerance

During the Mechanical run, the discharge temperature should be within the limitation.

During the test, the shaft seal portions except seal gas supply nozzles of the compressor will be open

to atmosphere.

2-11-5 Performance Check

The performance check will be done in the course of the mechanical run. The capacity will be measured in accordance with IS0 1217 with discharge emperature meets the trip setting temperature.

Because performance will be checked on air, the results will be converted to the actual gas operating conditions.

During the Performance Check, the discharge temperature will be varied according to inlet conditions.

3. Screw Compressor Testing - lnspection After Running Test

After completion of the test, the rotors and the rotor chamber will be visually inspected through the discharge nozzle. (The discharge side is under most severe conditions, and the visual inspection of the discharge side is a normal practice to check a rotor contact. )

Acceptance Criteria For Rotors

Judgment of acceptance will be done based on screw compressor manufacture experiences, when scratch marks are seen on the rotors. ( Slight scratch marks on the rotor sealing strips are normally expected to see. )

4. Screw Compressor Testing - Screw Compressor Shop Test Araangement

Following componenets are used for test from Shop Facilities:

  • Driver( Motor)
  • Couplings
  • Baseplate
  • Suction Filter
  • Suction Silencer
  • Discharge Silencer
  • Lube Seal Oail Unit (Include Oil Reservoir)
  • Piping
  • Instruments
  • Thrust Bearing T em perature Monitor
  • Casing Vibration Monitor

Following Components are used from job components:

  • Speed-up Gear
  • Thrust Bearing T em perature Thermocouple
  • Casing Vibration Detector

5. Screw Compressor Testing - Measurement Items

Following Items are measured in Heat Run, Mechanical Run and Performance Test:

  • Atmospheric Pressure
  • Atmospheric Temperature
  • Relative Humidity (Only in Performance Test)
  • Inlet Pressure
  • Inlet Temperature
  • Discharge Pressure
  • Discharge Temperature
  • Capacity (Orifice), (Only in Performance Test)
  • Up-Stream Temperature (Only in Performance Test)
  • Differential Pressure (Only in Performance Test)
  • Up-Stream Pressure (Only in Performance Test)
  • Lube and seal Oil Supply Pressure
  • Lube and seal Oil Supply Temperature
  • Lube and seal Oil Supply Drain Temperature
  • Compressor speed
  • Thrust Bearing temperature
  • Journal Bearing temperature
  • Casing Vibration
  • Noise Level

Measurement shall be made after bearing, lube oil and gas temperature have stabilized, and thereafter, at 30 minutes intervals for the duration of the test.

The shop instruments used for the tests receive periodic calibration and examination based on manufacture Quality Assurance System.

6. Screw Compressor Testing - Conversion Procedure Of Performance Test Data

As operating conditions in performance tests may not agree with those specified in the specification, conversion is required to estimate performance of compressors in the specified service at site. The screw compressor manufacture will submit performance calculation and conversion procedure of test data.


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