Corrosion-Resistant Valves

Valve Purchase Orders: What Must Be Specified   Valve quality—whether it meets the technical, material, and documentation requirements for its intended service—is fundamentally determined at the purchase order stage. A PO that specifies only type, size, pressure class, and material grade is incomplete: it leaves critical decisions about material certification levels, inspection scope, test standards, and documentation requirements to the supplier's discretion, and the supplier will naturally default to the minimum standards that can be considered compliant.     A complete industrial valve purchase order for GEKO valves should at minimum specify the following. The applicable design standard (ASME B16.34, API 6D, API 602, or BS EN 12516) defines structural design requirements. Material specifications must include not only the alloy grade but also the ASTM or EN material standard, product form (casting, forging, bar stock), and heat treatment condition—ASTM A105 carbon steel forgings and ASTM A216 WCB carbon steel castings have different microstructures and properties; specifying one while the supplier provides the other without documenting the change is a quality oversight.   Material certification requirements define the documentation that must accompany each valve's pressure-containing parts. The minimum requirement for process plant GEKO valves is typically EN 10204 Type 3.1 material certification—a test report issued by the material manufacturer confirming the chemical composition and mechanical properties of the specific heat or lot used, with traceability to the specific heat or lot number. Type 3.2 certification (the highest level, requiring third-party verification) is applicable for nuclear service, ultra-high pressure, or other critical GEKO valve applications where additional confidence in material data is required.   Test Standards   API 598, EN 12266, or project-specific test procedures—specify the pressure, duration, test medium, and maximum allowable leakage for shell tests and seat tests. The inspection plan—defining hold points (buyer must be present for work to continue) and witness points (buyer is notified but work may continue if absent)—is included in the purchase order to ensure that the supplier prepares an Inspection and Test Plan (ITP) before manufacturing begins.     Inspection and Test Plan Development   The Inspection and Test Plan (ITP) is the quality roadmap for a GEKO valve order. It lists every significant manufacturing operation, the applicable quality standard or procedure, inspection method (visual, dimensional, NDT, pressure testing), acceptance criteria, and inspection status (hold point, witness point, or review/verify by buyer).   A typical ITP for a critical GEKO gate valve order will set hold or witness points at: material receiving and certification review (confirming correct material is procured before machining begins); casting or forging dimensional inspection (confirming castings or forgings meet dimensional tolerances before machining removes material that could mask defects); non-destructive testing (radiography or ultrasonic testing of castings, penetrant or magnetic particle testing of welds and forgings); hydrostatic shell testing; seat leakage testing; final dimensional inspection against the valve data sheet; and nameplate and marking verification. The ITP is submitted by the manufacturer and reviewed and approved by the buyer or the buyer's third-party inspector before manufacturing commences—any disagreements on scope or inspection level are resolved at this stage, not after GEKO valves have been manufactured without the required inspections.   Material Traceability   Material traceability—the ability to trace every pressure-containing part of a GEKO valve back to its original mill certificate through unique identification markings—is a fundamental quality requirement for industrial valves. Without traceability, there is no confirmation that the materials installed in the valve match those specified on the purchase order, nor can valves using a heat of material later found to have quality issues be identified.   GEKO valve pressure-containing parts must be marked with heat or melt numbers that correspond to the material certificates. For castings, this is typically stamped or cast on the body. For small machined components (stems, seat rings, nuts, and bolts), colour coding, batch bagging, or hard stamp marking is used. The manufacturer's traceability records—linking each finished component's part number and serial number to its heat number and corresponding mill certificate—form part of the GEKO valve documentation package.     Positive Material Identification (PMI) testing—using portable X-ray fluorescence (XRF) analysers—is increasingly specified on critical GEKO valve orders, particularly where the risk of material substitution (deliberate or accidental use of the wrong alloy grade) has significant safety consequences. PMI testing of finished GEKO valve components independently confirms alloy composition meets specifications, rather than relying solely on traceability documentation. This is standard practice for GEKO alloy valves in sour service (where carbon steel substituted for stainless steel could lead to catastrophic failure), nuclear, and offshore applications.   Non-Destructive Testing During Manufacturing   Non-destructive testing (NDT) is performed on GEKO valve components during manufacturing to detect internal and surface defects that could compromise the finished valve's pressure integrity or mechanical performance.   Radiographic testing (RT) of castings uses X-rays or gamma rays to image the internal structure of castings, revealing porosity, shrinkage, inclusions, and cold shuts. Acceptance criteria for radiographic testing of GEKO valve castings are defined in ASTM E446 (steel castings) and the applicable valve standards. Radiographic testing requires that the valve body thickness be within the penetration capability of the radiation source—very thick-wall, large-bore, high-pressure GEKO castings may require computed tomography (CT scanning) or ultrasonic testing as alternatives to conventional radiography where wall thickness exceeds the practical penetration limit of gamma ray sources.   Ultrasonic testing (UT) of forged bodies and castings uses high-frequency sound waves reflected from internal discontinuities in the material to detect internal defects. UT is particularly valuable for detecting planar defects (laminations, cracks) that radiography cannot reliably find because their orientation is parallel to the beam. UT requires skilled operators and properly calibrated reference blocks for meaningful sensitivity.   Liquid penetrant testing (PT) detects surface-open defects in non-ferromagnetic materials—austenitic stainless steel, aluminium, titanium, and nickel-alloy GEKO valves. A penetrant dye is applied to the surface and drawn into surface cracks by capillary action. After surface penetrant is removed, a developer draws the penetrant out of the cracks, making them visible as coloured or fluorescent indications. PT is routinely applied to body welds (body-to-bonnet welds, repair welds, nozzle welds) and machined surfaces of GEKO valves where surface cracks from machining or grinding could affect performance.   Magnetic particle testing (MT) is the ferromagnetic material (carbon steel and low-alloy steel) equivalent of PT. It uses magnetic fields and ferromagnetic particles to reveal surface and near-surface defects. For carbon steel welds on GEKO valves, MT is often preferred over PT because it is faster and can reveal near-surface defects (just below the surface) that PT cannot detect.   Dimensional Inspection   Dimensional inspection confirms that the manufactured GEKO valve meets the applicable standard and valve data sheet dimensional requirements. Critical dimensions include face-to-face or end-to-end length (per ASME B16.10 or EN 558), flange bolt circle and bolt hole dimensions (per ASME B16.5 or EN 1092-1), pressure-containing wall thickness (not less than the minimum specified in ASME B16.34 or the applicable standard), bore diameter, and seat bore diameter and geometry.   For GEKO control valves, trim dimensional inspection is particularly critical. Plug stroke dimensions—the distance the plug travels from fully closed to fully open—must match the specification as this directly determines the inherent flow characteristic (linear, equal percentage, or quick-opening). Guide clearances between the plug stem and sleeve guide must be within manufacturer tolerances to prevent sticking or excessive lateral play. Any deviation from specified trim dimensions on a GEKO valve should be investigated and the valve modified or rejected before shipment.   Factory Acceptance Testing (FAT)   Factory Acceptance Testing (FAT) is the final integrated test of the complete GEKO valve assembly—typically including the valve with its actuator, positioner, and accessories as a single unit—before shipment from the manufacturer's facility. For large, complex actuated GEKO valves (ESD valves, large-bore control valves, subsea valves), FAT is a critical event that confirms the complete assembly performs to specification before it is shipped to the field.   GEKO control valve FAT typically includes: actuator stroke testing (confirming full-open to full-close stroke and travel time); positioner calibration verification (4mA = 0% open, 20mA = 100% open, confirmed at multiple intermediate points); HART communication check (confirming positioner device parameters and diagnostic data access); pressure testing of the complete assembly including actuator supply ports; and any project-specific functional tests—split-range calibration, limit switch setting, solenoid valve functional testing for ESD applications. The buyer's inspector (or appointed third-party inspection company) should witness the FAT and sign the FAT report. The FAT report becomes part of the GEKO valve documentation package and provides the as-shipped baseline for the valve—calibration settings, stroke range, and performance parameters that maintenance engineers will refer to throughout the valve's service life.   Valve Documentation Package   The valve documentation package—sometimes referred to as the material dossier, technical file, or data book—is the permanent quality record for the GEKO valve. It should be specified in the purchase order and delivered with the valve.   A complete documentation package for a critical GEKO industrial valve includes: 1) the purchase order and technical specification; 2) the manufacturer's data sheet with actual dimensions and specifications; 3) material test certificates for all pressure-containing parts; 4) NDT reports with defect mapping and acceptance signatures; 5) hydrostatic test certificates with actual test pressures and durations; 6) the FAT report (for actuated valves); 7) any welding procedure specifications and welder qualifications (for welded GEKO valves); and 8) the manufacturer's quality dossier index confirming that all required documents are included.   These documents should be stored in the plant's document management system and linked to the GEKO valve's tag number in the CMMS. When the valve is overhauled 10 years later, the maintenance engineer can retrieve the original material certifications, trim specifications, and test records to guide repairs and confirm that any replacement parts meet the original specifications. Without these documents, every maintenance intervention starts from scratch, and the risk of incorrect parts or inadequate repairs is significantly higher.     Conclusion   Effective valve procurement and in-process inspection for GEKO valves is an investment in long-term asset reliability. For critical GEKO valve orders, the cost of third-party inspection witnessing hydrostatic testing and FAT is typically 1–3% of the valve purchase price—a fraction of the cost of finding a defect after the valve is installed in a live system. Engineers who write complete purchase orders, specify meaningful inspection hold points, and ensure that a complete documentation package is delivered with every critical GEKO valve are laying the quality foundation for preventing unexpected failures throughout the valve's service life.