| Compressor Type and Process Duty |
| Compressor configuration | Reciprocating, centrifugal, axial, diaphragm, or screw design | API 618 for reciprocating compressors; API 617 for axial, centrifugal, and expander-compressors | Approved compressor data sheet, process flow diagram, compressor performance map, and operating philosophy | Match the compressor design to gas composition, pressure ratio, flow variation, pulsation sensitivity, and required turndown | Required |
| Gas composition | Component analysis, molecular weight, compressibility, corrosive contaminants, toxicity, and flammability | Process safety specification; material compatibility and hazardous-area requirements should be included in the purchase specification | Current gas analysis, safety data sheet, contaminant limits, and design-case composition | Use the worst credible gas composition for mechanical, thermal, sealing, and power calculations | Required |
| Capacity and pressure | Inlet pressure, discharge pressure, flow rate, suction temperature, discharge temperature, and allowable pressure fluctuation | API 618 or API 617, depending on compressor type; local pressure-equipment legislation may also apply | Guaranteed operating points, rated flow basis, pressure-ratio calculation, and performance test procedure | Check normal, minimum, maximum, start-up, shutdown, recycle, and emergency cases | Required |
| Continuous versus intermittent operation | Annual operating hours, start-stop frequency, load cycles, and expected service life | Vendor design basis and applicable API inspection, testing, and documentation requirements | Lifecycle calculation, maintenance intervals, expected component life, and spare-parts recommendation | Frequent cycling can affect valves, seals, bearings, couplings, and control-system sizing | Recommended |
| API 618 Verification for Reciprocating Compressors |
| Mechanical design | Frame, cylinders, crankshaft, connecting rods, distance pieces, pulsation bottles, and lubrication systems | API 618 | Compliance statement, mechanical design calculations, materials list, stress analysis, and inspection plan | Confirm the offered configuration is designed for the specified gas and all stated operating cases | Required |
| Pulsation and vibration control | Allowable pulsation, piping forces, acoustic response, structural response, and skid vibration limits | API 618 pulsation and vibration study requirements | Preliminary and final pulsation study, mechanical response analysis, piping-load report, and field measurement plan | Require the study to cover the complete compressor, bottle, piping, support, and operating-speed system | Required |
| Lubrication and contamination control | Lubricated or oil-free cylinder operation, lubricant type, oil carryover target, and separation equipment | API 618; product cleanliness may also require ISO 8573-1 | Oil carryover guarantee, lubricant compatibility statement, separator performance data, and cleanliness test method | For oxygen, hydrogen, food, pharmaceutical, or catalyst-sensitive service, confirm whether oil-free compression is mandatory | Conditional |
| API 617 Verification for Centrifugal and Axial Compressors |
| Aerodynamic performance | Flow range, head, efficiency, surge margin, choke limit, speed range, and operating envelope | API 617 | Performance map, guaranteed efficiency, surge-control philosophy, test code, and correction methodology | Evaluate the complete operating range, not only the design point; confirm stable operation during start-up and recycle | Required |
| Rotor dynamics | Critical speeds, stability, unbalance response, bearing design, and torsional behavior | API 617 | Rotor-dynamics report, critical-speed separation margins, stability analysis, and torsional analysis where applicable | Review the driver, gearbox, coupling, compressor train, and control system as one rotating train | Required |
| Sealing system | Dry gas seal, oil seal, labyrinth seal, buffer gas, separation gas, and vent arrangement | API 617 with project-specific seal-system requirements | Seal datasheet, seal-gas quality requirements, leakage limits, vent routing, and failure-mode response | For toxic or flammable gases, define containment, vent recovery, detection, and emergency isolation requirements | Required |
| ISO 8573-1 Compressed-Gas Purity and Contamination Control |
| Particle purity class | Specify the required ISO particle class at the defined measurement location | ISO 8573-1, Particles Class 0 through Class 5 | Particle-count test report identifying particle-size ranges, sampling location, instrument, and calibration status | Do not state only “clean gas”; specify the class and the point of compliance | Conditional |
| Water purity class | Pressure dew point or liquid-water limit | ISO 8573-1: Class 1 pressure dew point not higher than −70°C; Class 2 not higher than −40°C; Class 3 not higher than −20°C; Class 4 not higher than 3°C; Class 5 higher than 3°C; Class 6 liquid water not exceeding 10 mg/m³ | Dew-point test report, pressure and temperature at sampling, dryer data, and condensate-management method | Select the class according to downstream valves, instruments, catalysts, pipelines, and ambient conditions | Conditional |
| Oil purity class | Total oil, including liquid oil, aerosol, and vapor | ISO 8573-1: Class 1 ≤0.01 mg/m³; Class 2 ≤0.1 mg/m³; Class 3 ≤1 mg/m³; Class 4 ≤5 mg/m³; Class 0 is user- or equipment-defined; Class X is above Class 4 | Total-oil test report, sampling procedure, oil-separation specification, and lubricant details | Oil-free compression does not automatically guarantee a stated ISO oil class; require measured evidence at the specified outlet | Conditional |
| Point of compliance | Compressor discharge, aftercooler outlet, dryer outlet, or final user connection | ISO 8573-1 classification must identify the measurement location and test conditions | Sampling plan, sample-line design, test date, operating load, pressure, temperature, and laboratory or instrument details | Purity can change through piping, receivers, filters, dryers, and condensate drains; define one or more control points | Required |
| ATEX and Hazardous-Area Compliance |
| Equipment intended for explosive atmospheres | Equipment group, category, gas or vapor zone, gas group, temperature class, and protection concept | ATEX Directive 2014/34/EU for equipment and protective systems intended for use in potentially explosive atmospheres | EU Declaration of Conformity, ATEX marking, certificate number where applicable, technical file reference, and instructions | ATEX is an EU market requirement; confirm the destination-country legislation and the site hazardous-area classification | Required |
| Hazardous-area suitability | Zone 0, 1, or 2; gas group IIA, IIB, or IIC; temperature class; ambient-temperature range | ATEX equipment category and protection marking must be suitable for the classified area and gas hazard | Area-classification drawing, equipment marking, certificate scope, surface-temperature data, and ambient limits | Equipment selected for Zone 2 is not automatically suitable for Zone 1 or Zone 0 | Required |
| Electrical and instrumentation package | Motors, junction boxes, transmitters, switches, solenoid valves, analyzers, and control panels | ATEX conformity for each applicable item; installation may also require national electrical and wiring rules | Component certificates, complete equipment schedule, wiring diagrams, cable-gland approvals, and inspection certificates | Verify the complete package, not only the compressor body; mismatched components can invalidate the installation | Required |
| Ignition-source control | Maximum surface temperature, hot-gas discharge, mechanical sparks, static electricity, bearings, seals, and overspeed protection | ATEX risk assessment and applicable protection concept | Ignition-hazard assessment, temperature-rise data, grounding and bonding test, overspeed trip test, and alarm/trip matrix | Review abnormal conditions such as blocked discharge, loss of cooling, seal failure, reverse rotation, and high vibration | Required |
| Reliability, Testing, and Documentation |
| Factory acceptance testing | Mechanical run test, performance test, overspeed test where applicable, vibration test, and control-system test | Applicable requirements of API 618 or API 617 and the approved project inspection and test plan | Signed test procedure, calibrated-instrument list, raw test data, vibration spectra, deviation log, and final test certificate | Define witness and hold points before purchase order placement | Required |
| Materials and inspection | Pressure-containing materials, weld procedures, non-destructive examination, hardness, and traceability | API 618 or API 617 plus project material and inspection specifications | Material certificates, welding records, NDE reports, heat-treatment records, dimensional reports, and positive-material-identification records where required | Use enhanced inspection for toxic, hydrogen, oxygen, high-pressure, or highly corrosive service | Recommended |
| Control and protection system | Anti-surge control, recycle control, shutdowns, vibration monitoring, temperature monitoring, pressure trips, and emergency-stop logic | API project requirements, API 617 or API 618, functional-safety specification where applicable, and hazardous-area requirements | Cause-and-effect matrix, logic diagrams, alarm and trip set points, proof-test procedures, and cybersecurity requirements | Set points should protect the machine without causing unstable operation or unnecessary trips | Required |
| Documentation package | Operating manuals, maintenance manuals, drawings, certificates, spare-parts lists, and commissioning procedures | Purchase specification, API documentation requirements, ISO 8573-1 test records where specified, and ATEX documentation where applicable | Final certified drawings, data book index, compliance matrix, recommended spare parts, training records, and as-built documents | Make document delivery and approval a contractual milestone before shipment | Required |
| Lifecycle support | Critical spares, service response, local maintenance capability, obsolescence plan, and training | Project reliability and maintainability requirements | Recommended-spares list by operating year, maintenance schedule, tooling list, training plan, and service contact procedure | Compare total cost of ownership rather than purchase price alone | Recommended |