MEP · 14 checks

Process Pipework
QA inspection checklist

Industrial and process pipework installation quality audit.

Every check below carries what good looks like, when it passes, the standard it comes from and the defects that usually fail it. That guidance is what turns a tick-box into an inspection.

Materials & Fabrication

  1. 1.
    Pipe material and grade match specification
    What to look forPipe stamped with material grade (e.g. P235GH, 316L, A106 Grade B) matching spec. EN 10204 Type 3.1 mill cert traceable to heat number on each pipe length. Material type-tested per process fluid compatibility.
    Acceptable whenPer PD 5500 / ASME B31.3: material grade per process design. EN 10204 Type 3.1 inspection certificate mandatory for pressure systems. CE/UKCA / PED Category III+ requires Type 3.2 (third-party witnessed).
    StandardPD 5500:2024 — Specification for unfired pressure vessels. ASME B31.3 — Process piping. BS EN 10204:2004 — Inspection documents. PSSR 2000 (Pressure Systems Safety Regulations).
    Common defectsType 2.2 cert supplied where 3.1 specified — not traceableWrong grade — incompatible with process fluidHeat number rubbed off — cannot verifyMill cert covers different cast than supplied pipeNo certification for fittings / flanges
  2. 2.
    Pipe wall thickness correct for pressure rating
    What to look forPipe schedule (Sch 40, 80, 160, XS, XXS) per spec. Wall thickness verified by ultrasonic gauge or caliper at multiple points. Schedule stamp visible on pipe. Corrosion allowance included.
    Acceptable whenPer ASME B31.3 / PD 5500: wall thickness ≥ design (pressure + corrosion allowance + manufacturing tolerance). Tolerance per BS EN 10216 (seamless) / 10217 (welded). UT verification on heavy-wall.
    StandardASME B31.3 / PD 5500. BS EN 10216 / 10217.
    Common defectsWrong schedule — pressure rating below designManufacturing tolerance ignored — thinnest point below specCorrosion allowance not includedThinning at induction bends not checkedNo UT records
  3. 3.
    Weld procedures qualified (WPS/PQR)
    What to look forWelding Procedure Specification (WPS) and Procedure Qualification Record (PQR) for each weld type — material/thickness/process/position. Reviewed and approved by inspecting authority. Used welders qualified to specific WPS.
    Acceptable whenPer BS EN ISO 15614 (qualification) / BS EN ISO 15609 (specification): WPS approved before any production weld. PQR demonstrates compliance with mechanical / NDT acceptance. ASME IX equivalent in US-spec systems.
    StandardBS EN ISO 15614-1:2017 — WPS qualification by procedure test. BS EN ISO 15609-1:2019 — WPS. ASME Section IX.
    Common defectsNo WPS — welder making it upPQR missing — process not validatedWPS does not cover the actual material thicknessWrong welding position certified vs usedWPS approved by wrong authority
  4. 4.
    Welders hold valid qualifications
    What to look forWelder qualifications per BS EN ISO 9606 (steel) / ASME IX. Coverage of process (TIG/MMA/MAG), material group, thickness, position, joint type. Card / certificate in date — typically 2-3 years validity. Welder identification stamp on weld root.
    Acceptable whenPer BS EN ISO 9606-1 / ASME IX: welder qualified for the actual joint configuration. Validity 2-3 years subject to continuity (welder must produce welds within scope every 6 months).
    StandardBS EN ISO 9606-1:2017 — Welder qualification (steel). ASME Section IX.
    Common defectsWelder card expired — re-qualification neededWrong process / material qualificationNo continuity record — qualification lapsedWelder ID stamp missing on weldsOne welder qualifying for whole team

Installation

  1. 5.
    Pipework routed per isometric drawings
    What to look forPipe routing matches the latest revision of the isometric drawings. Spool numbers / weld numbers cross-reference to the iso. Route accommodates expansion, drainage, venting, and access for valves / instrumentation.
    Acceptable whenPer ASME B31.3 / project specification: route as design. Slope to drain/vent points typical 1:200 minimum. Access for maintenance per spec. Each weld assigned a unique number.
    StandardASME B31.3. PD 5500. Project Engineering Standards.
    Common defectsSite routing varies from iso — no engineering re-checkPipe traps (no drainage) — water hammer / cavitationNo access to valve handleWelds not numbered — NDT records cannot be linkedSpool fabrication misaligned with site supports
  2. 6.
    Supports and hangers at correct centres and type
    What to look forSupports per design — pipe shoes, U-bolts, spring hangers, sliding plates per stress analysis. Spacing per ASME B31.3 Table 121.5 (or design). Cold-set per stress isometric. No rigid restraint where flexibility required.
    Acceptable whenPer ASME B31.3 Table 121.5: support spacing function of pipe size and material — typical NPS 4 carbon steel ~ 5 m (water service). Spring hangers cold-set per pipe stress design.
    StandardASME B31.3. MSS SP-58 — Pipe hangers and supports. PD 5500.
    Common defectsSpacing exceeds Table 121.5 — pipe sagsWrong support type (rigid where flexible needed)Spring hanger not cold-setNo allowance for thermal movementSupport seats damaged / corroded
  3. 7.
    Expansion loops / bellows installed where required
    What to look forExpansion loops, expansion bends, or bellows installed per stress design at high-temperature service. Bellows fitted with tie rods / lateral guides per manufacturer. Anchor and guide positions per design.
    Acceptable whenPer ASME B31.3 / EJMA Standards (bellows): expansion devices sized for thermal range. Bellows installed in correct orientation; tie rods removed only after pressure test if "shipping" type. Anchors and guides positioned per design.
    StandardASME B31.3. EJMA Standards (Expansion Joint Manufacturers Association). PD 5500.
    Common defectsBellows installed without tie-rod removal — no movement allowedAnchor missing — pipe walksGuide too far from bellows — bellows squirm under pressureBellows orientation wrong (axial vs lateral)No expansion device on long hot run — failure on first thermal cycle
  4. 8.
    Flanged joints torqued to specification
    Record: Torque (Nm)
    What to look forFlanged joints made up with calibrated torque wrench, in correct sequence (cross-pattern, multiple passes). Bolt/nut/washer per spec. Gasket type / thickness per process. Torque values per ASME PCC-1 / manufacturer.
    Acceptable whenPer ASME PCC-1 Appendix K: torque per bolt material / size / gasket / system pressure. Cross-pattern tightening in 3-4 passes. Tightening witnessed and recorded. Hot-bolting after thermal cycle for high-temp service.
    StandardASME PCC-1:2019 — Pressure boundary bolted flange joint assembly guidelines. ASME B16.5 (flanges).
    Common defectsBolts torqued in linear sequence — gasket compressed unevenlySingle-pass torque to final value — no relaxationNo torque recordWrong bolt grade (B7 substituted with mild steel)No hot-bolting after start-up
  5. 9.
    Valves correct type and orientation
    What to look forValve type (gate, globe, ball, check, butterfly) per process. Body material / pressure rating per spec. Flow arrow on body matches design flow direction. Stem orientation accessible. Tag matches P&ID.
    Acceptable whenPer process spec / ASME B16.34 (valves): valve type, material, and rating per design. Flow direction correct (especially for check valves). Tag matches P&ID. Bonnet / stem accessible.
    StandardASME B16.34:2020 — Valves: Flanged, threaded and welding end. API 600/602/603 (specific valve types).
    Common defectsCheck valve installed reversed — no flowValve tag does not match P&IDWrong material body — corrosion in serviceStem horizontal — cannot operate without ladderGlobe valve with flow opposite to stem closure — chatter

Testing & Inspection

  1. 10.
    Pressure test completed and held
    Record: Test pressure (bar)
    What to look forHydrostatic test at 1.5× design pressure (or 1.25× for retest), held for 30 minutes minimum. Calibrated test gauge. No measurable drop after thermal correction. Vents and drains clear before test. Test water quality per spec.
    Acceptable whenPer ASME B31.3 Section 345 / PD 5500: hydrostatic 1.5× design × (Sa/Sb) ratio; minimum 30-minute hold; no leaks. Pneumatic only by exception with safety case (compressible energy hazard).
    StandardASME B31.3 Section 345. PD 5500 Section 5. PSSR 2000.
    Common defectsPressure drop > permitted — leak somewherePneumatic test without safety case — risk to personnelTest gauge uncalibratedHold time cut shortTest water dirty / chlorinated for stainless — pitting corrosion
  2. 11.
    NDT (radiography/UT) completed on welds
    What to look forNDT per project NDT plan — typically radiography (RT), phased array UT (PAUT), magnetic particle (MT), or dye penetrant (PT). Coverage % per service category (typically 10-100% RT for high-pressure / aggressive service). Reports per weld with images.
    Acceptable whenPer ASME B31.3 Table 341.3.2 / PD 5500: NDT coverage and acceptance criteria per service category — Normal Fluid Service typically 5% RT random; Severe Cyclic / Category M / High Pressure 100%. NDT operators PCN / ASNT certified.
    StandardASME B31.3 Section 341 / Table 341.3.2. PD 5500 Annex T. BS EN ISO 17636 (RT). BS EN ISO 17640 (UT).
    Common defectsNDT coverage below project requirementOperator not certified (PCN / ASNT)Films / images not stored — disputesWeld defects identified but not repaired / re-shotRadiography density / sensitivity inadequate
  3. 12.
    Visual weld inspection — no defects
    What to look forVisual inspection of every weld — face profile, cap reinforcement, undercut, root concavity (where accessible), spatter, arc strikes. Reinforcement smooth, no sharp toe undercut. Root pass verified by NDT or boroscope where 100% required.
    Acceptable whenPer ASME B31.3 Table 341.3.2 / BS EN ISO 5817 (quality levels): Level B for severe service, Level C standard, Level D non-pressure. Weld profile within tolerance. Cap reinforcement ≤ 3 mm typical.
    StandardBS EN ISO 5817:2014 — Welding quality levels. ASME B31.3 Section 341. BS EN ISO 17637 (visual testing).
    Common defectsToe undercut > 0.5 mm — stress concentration, fatigue crackArc strikes outside weld zoneCap reinforcement excessive — flow disturbanceSpatter not removedCrater pipe at weld stop — no fill
  4. 13.
    Flushing and cleaning completed
    What to look forSystem flushed with appropriate medium (water, air, steam) at design velocity to remove construction debris. Filter mesh / screen on pump suction caught debris. Cleanliness verified by visual inspection / particle count where critical.
    Acceptable whenPer ASME B31.3 / project commissioning: flushing velocity to achieve turbulent flow (typically Re > 4000); duration until cleanliness criterion met. Particle count for clean / hydraulic systems per ISO 4406. Acid pickle / passivation for stainless if needed.
    StandardASME B31.3 Section 350. ISO 4406:2021 — Particulate cleanliness. Manufacturer commissioning procedures.
    Common defectsFlushing velocity below turbulent — debris not liftedNo cleanliness target — disputesStrainers not removed after flushing — high pressure drop in serviceStainless not passivated — surface contamination, future corrosionDebris from flushing dumped to drain without permit
  5. 14.
    Insulation applied to specification
    What to look forInsulation type (mineral wool, calcium silicate, foam glass, aerogel) per process temperature. Thickness per BS 5422 / project. Vapour barrier on cold service. Cladding (aluminium, stainless) sealed against weather. Hot/cold service segregated.
    Acceptable whenPer BS 5422 / PIP INTG1000: insulation thickness function of process temp, ambient, surface temp limit (typically 60°C for personnel protection). Vapour barrier sealed on cold service to prevent ice / condensation.
    StandardBS 5422:2009 — Specifying thermal insulation. PIP INTG1000 — Insulation general guidelines. CINI Manual.
    Common defectsInsulation thickness below spec — heat loss / surface temp too highNo vapour barrier on cold service — ice / corrosion under insulationCUI (Corrosion Under Insulation) not protected againstCladding gaps — water entryHot and cold service insulation mixed up

Questions people ask

What is a process pipework QA inspection for?

To record that the work was checked against the specification before it was covered up or handed over: a pass or fail against each item, a measurement where one matters, and a photo where it failed. It is the evidence a client's quantity surveyor or clerk of works asks for, and the thing that settles the argument at final account.

What standards does this checklist check against?

Each item names its reference. On this checklist that includes PD 5500:2024, ASME B31.3 / PD 5500. BS EN 10216 / 10217., BS EN ISO 15614-1:2017, BS EN ISO 9606-1:2017, ASME B31.3. PD 5500. Project Engineering Standards., ASME B31.3. MSS SP-58. The contract specification and the approved drawings always take precedence over a general standard; where they say something stricter, inspect to that.

Who signs a QA inspection off?

The person who carried out the check, named and dated, and where the contract calls for it the client's representative as a witness. The signature records that the check was done and what was found. It is not a warranty of the work.

How many items are on it, and do I have to use them all?

14 checks across 3 sections. Delete what does not apply to the job and add anything the specification asks for that is not here. A checklist that has plainly been thought about carries more weight than a long one nobody read.

Is this useful for a subcontractor as well as a main contractor?

More so. The subcontractor is the one who gets asked to come back and open something up. A signed inspection sheet with photos at the time is the cheapest insurance on a construction site.

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