Inspection &
Testing System
Every valve tested to API 598 / ISO 5208 before despatch. This page defines every test type, every standard applied, every measurement recorded — and how third-party inspection is co-ordinated.
Pressure & Leakage Tests — Applied to Every Valve
All five pressure tests below are conducted per the referenced standard. Results are recorded and reported. Tests marked as Critical are mandatory on every valve — no exceptions.
Hydrostatic Shell Test
API 598 / ASME B16.34 / API 6D
Purpose
Verifies the pressure-integrity of the valve body, bonnet, cover, and all pressure-retaining parts under test pressure exceeding the rated working pressure.
Procedure
- Test pressure: 1.5× rated pressure per ASME B16.34 pressure-temperature table for the material group
- Test medium: water (with or without rust inhibitor) or kerosene for hydrophobic applications
- Test duration: minimum 60 seconds (Class 150–600), 120 seconds (Class 900–2500) per API 598 Table 4
- Valve position: gate valves — disc partially open; ball/plug/butterfly — partially open during shell test
- Acceptance: zero leakage from body, bonnet, gland packing (no visible seepage or pressure drop)
Leakage Criteria
Zero — no visible leakage permitted
Report Contains
- Test pressure (MPa / bar / psi)
- Test duration (seconds)
- Test medium
- Valve position during test
- Result: Accept / Reject
- Tester name and date
- Inspector / witness signature
Seat Leakage Test
API 598 / ISO 5208 / API 6D
Purpose
Verifies the sealing capability of the valve seat under operating pressure — confirms the valve will isolate flow when closed in service.
Procedure
- Test pressure: rated working pressure (API 598) or as specified — lower pressure air test at 0.6 MPa (6 bar) also common
- Test medium: water (liquid seat test) or nitrogen / clean dry air (gas seat test)
- Test duration: 15–60 seconds depending on valve size and class per API 598 Table 4
- Valve position: fully closed — both upstream and downstream seat tested for bidirectional valves
- Leakage measurement: drops per minute or cc per minute collected at downstream port
Leakage Criteria
- —API 598 Class IV (default): 0.18 × DN cc/min for liquid; 1.8 × DN cc/min for gas
- —Class V (tight shutoff): 0.0006 × DN × ΔP cc/min
- —Class VI (bubble-tight, soft seats): zero leakage or bubbles per ANSI/FCI 70-2
Report Contains
- Test pressure and medium
- Duration
- Leakage measured (cc/min or drops/min)
- Leakage class achieved
- Upstream and downstream results
- Result: Accept / Reject
Backseat / Stem Seal Test
API 598 / BS 5146
Purpose
Verifies the backseat sealing in gate and globe valves — confirms stem seal integrity when valve is in fully open position, allowing packing replacement under pressure.
Procedure
- Applicable to: gate valves, globe valves with backseat provision
- Valve position: fully open — backseat engaged
- Test medium: water or gas as per shell test medium
- Test pressure: same as shell test pressure (1.5× rated)
- Gland packing loosened to allow leak detection from backseat
- Duration: minimum 60 seconds
Leakage Criteria
Zero — no leakage past backseat when gland is loose
Report Contains
- Test pressure
- Duration
- Gland condition (loosened)
- Result: Accept / Reject
Low-Pressure Seat Test (Pneumatic / Air Test)
API 598 / ISO 5208 / Client spec
Purpose
Detects small seat leakages at low differential pressure — represents operating conditions in gas service where small leakage rates matter.
Procedure
- Test pressure: 0.6 MPa (6 bar) nitrogen or clean dry air
- Applied to: soft-seated ball valves (PTFE/PEEK seats), butterfly valves with elastomer seats
- Bubble detection: downstream immersed in water — bubbles counted over timed period
- Leakage rate reported in bubbles/minute per API 598 Table 5
Leakage Criteria
Zero visible bubbles (bubble-tight) or within API 598 Class VI limits
Report Contains
- Test pressure (6 bar air)
- Duration
- Bubble count / leakage rate
- Result: Accept / Reject
Functional / Operational Test
API 598 / API 6D / Client spec
Purpose
Confirms the valve operates correctly through full travel — open to close to open — under controlled conditions before despatch.
Procedure
- Manual operation: handwheel or wrench — confirmed full travel with reasonable force
- Gear-operated: gear operator torque checked against design torque
- Actuated valves: full open/close cycle under rated actuator supply pressure/current
- Positioner calibration: span, zero, input signal confirmed (4-20mA / on-off)
- Limit switch function: open/close indication confirmed correct
- Solenoid valve function: energise/de-energise cycle confirmed
Leakage Criteria
N/A — operational functionality confirmed
Report Contains
- Operation method (manual/gear/actuator)
- Torque or operating force
- Full travel confirmation
- Limit switch / positioner calibration results
Inspection Scope — Material, Visual & NDT
Positive Material Identification (PMI — XRF)
Standard: ASTM material specifications / Client spec
Scope
All stainless steel (SS 316, 316L, 304), duplex, super duplex, Hastelloy C-276, Inconel 625, Monel 400, Titanium Gr2, and alloy trim components
Method
X-ray fluorescence (XRF) spectrometry — non-destructive, no surface damage
What We Check
- Element-by-element composition reading: Cr, Ni, Mo, Mn, Si, Cu, Co
- Comparison against ASTM minimum and maximum specification limits
- Pass / Fail per specification for each element
- PMI performed on: body, bonnet, disc/ball/gate, stem — all wetted alloy parts
- Instrument calibration reference on report
Why It Matters
Eliminates wrong-alloy risk — critical for chemical, sour service, cryogenic, and high-temp applications where alloy substitution could cause catastrophic failure.
Dimensional Inspection
Standard: ASME B16.5, B16.10, B16.47 / EN 558, EN 1092-1 / API 6D
Scope
Every valve — all pressure classes
Method
Calibrated measuring instruments: vernier callipers, bore gauges, thread gauges, surface plate
What We Check
- Face-to-face dimension per ASME B16.10 / EN 558 Series 1/2
- Flange OD, bolt-circle diameter, bolt hole count and diameter per ASME B16.5 / B16.47
- Bore diameter: full bore (FB) or reduced bore (RB) per API 6D / datasheet
- Stem diameter and thread form verification
- ISO 5211 actuator mounting flange centreline and bolt pattern
- Thread gauging: NPT, BSP, BSPT per ASME B1.20.1 / ISO 7-1
Why It Matters
Ensures valve fits the piping system as designed — dimensional non-conformances are a common source of field installation failures.
Visual Inspection
Standard: MSS SP-55 / API 598 / ASTM A488
Scope
Every valve — body, bonnet, disc/ball, handwheel, painting, identification markings
Method
Trained inspector visual assessment against acceptance criteria
What We Check
- Casting surface quality per MSS SP-55 Type I-VIII defect classification
- No cold shuts, misruns, hot tears, or open shrinkage above acceptance limit
- Paint / coating coverage, adhesion, colour per specification
- Identification marking: valve size, pressure class, material designation, flow direction arrow, manufacturer mark
- End protections: bore caps and flange/thread protectors correctly fitted
- Handwheel / actuator assembly — no physical damage
Why It Matters
Surface defects on castings can mask internal porosity or reduce wall thickness below minimum. Identification marking errors cause specification-traceability failures at site.
NDT Co-ordination (RT / UT / MT / PT)
Standard: ASME B16.34 / API 6D / ASTM E165 / ASTM E709
Scope
On request or per project specification — not standard unless specified
Method
Co-ordinated with approved NDT service provider — third-party NDT agencies
What We Check
- RT (Radiographic Testing): detects internal casting defects (porosity, inclusions, shrinkage) — critical for Class 900 and above
- UT (Ultrasonic Testing): detects sub-surface laminations and thickness verification
- MT (Magnetic Particle Testing): detects surface and near-surface defects in ferromagnetic materials
- PT (Liquid Penetrant Testing): detects surface-breaking defects in non-ferromagnetic and ferromagnetic materials
- Acceptance criteria per ASME Section VIII / API 6D / client spec
Why It Matters
Required for critical service: ASME B16.34 Class 900+, sour service, high-temperature high-pressure applications where casting defects could cause in-service failure.
Coating / DFT Inspection
Standard: ISO 12944 / SSPC / Client paint specification
Scope
For painted, coated, and FBE-coated valves
Method
Calibrated digital DFT gauge (dry film thickness), holiday detector for FBE
What We Check
- Surface preparation grade confirmed: Sa 2.5 (near-white blast) / St 3 (power tool clean)
- Primer DFT measured — minimum specified per paint system
- Intermediate coat DFT measured — minimum specified
- Finish coat DFT measured — minimum specified, total DFT calculated
- Holiday test for FBE: DC high voltage, 100V per 25 micron DFT
- Paint colour confirmation against RAL code or client standard
Why It Matters
Coating failures are a leading cause of external corrosion in plant environments. Correct DFT and adhesion prevent in-service failures, particularly for buried, offshore, and chemical plant valves.
TPI Co-ordination
Third-party inspection at any stage — material receiving, in-process, pressure testing, dimensional, or pre-despatch — is fully welcomed and co-ordinated by our quality team.
For TPI orders, an Inspection Test Plan (ITP) is prepared before production commences, submitted to the client and TPI agency, and agreed with designated witness (W) and hold (H) points before any test is conducted.
Hold Point enforcement: No production stage advances past a Hold (H) point without written release from the TPI inspector. This is operationally enforced — not a policy statement.
TPI Agencies We Co-ordinate With
Inspection Co-ordination Includes:
- ITP preparation and submission (before production)
- Inspector notification and scheduling
- Facility access and test equipment provision
- Test records presented to inspector at witness points
- Punch list compilation and closure
- Inspection Release Note (IRN) co-ordination
- All TPI costs managed (unless otherwise agreed)
Inspection & Testing FAQ
What is API 598 valve testing?
API 598 is the American Petroleum Institute standard for valve inspection and testing. It specifies test pressures (1.5× rated for shell, rated for seat), test durations (15–120 seconds depending on size and class), acceptable leakage rates by valve size and leakage class, and documentation requirements. API 598 is the primary production testing standard for ball, gate, globe, butterfly, check, and plug valves. Vajra applies API 598 to all production testing as standard.
What leakage class is standard, and how do I specify a different class?
API 598 Class IV is the default leakage class for most valve types — this allows a small measured leakage rate acceptable for most process applications. For tight shutoff applications (control valves, steam service), Class V or Class VI (bubble-tight, soft-seat valves) should be specified at RFQ stage. The leakage class is confirmed in the quotation and tested and recorded on the seat leakage test report.
What is PMI and on which valves is it performed?
PMI (Positive Material Identification) uses XRF spectrometry to verify alloy composition against the material specification. Vajra performs PMI on all alloy valves as standard: SS 316/316L, Duplex 2205, Super Duplex 2507, Hastelloy C-276, Inconel 625, Monel 400, and Titanium Gr2. PMI is available on CS valves on request. Results are element-by-element with pass/fail against ASTM specification limits.
Can I specify NDT (radiography, ultrasonic) on my valve order?
Yes. RT (radiographic testing), UT (ultrasonic testing), MT (magnetic particle), and PT (liquid penetrant) are available as part of the inspection scope — specified at RFQ stage or in the purchase order. Acceptance criteria are agreed per ASME Section VIII, API 6D, or client specification. NDT adds to lead time and cost — include in your RFQ for a quotation with NDT scope included.
Specify Inspection Requirements in Your RFQ
Include your TPI agency, leakage class, PMI requirements, NDT scope, and documentation needs in your RFQ. We confirm the full inspection scope in the quotation.