Based on the historical data of major petrochemical companies, it is evident that the quality of valves used in the petrochemical industry plays a crucial role in accidents, loss reduction, and elimination. Valve manufacturers conduct rigorous inspections to ensure product quality. However, even with these precautions, various issues still arise during on-site acceptance by purchasers.
█ Accompanying Documents.
The Accompanying documents mainly includes:
- Material certification for the main pressure-bearing parts of the valve (analysis of material chemical composition, mechanical performance testing, etc.)
- Manufacturing unit name and manufacturing license number
- Product name, model, specifications
- Product number, execution standard, and manufacturing date
- Applicable medium and temperature range
- Inspection conclusion and inspection date
- Valve inspection and test documents (may include valve supervision and inspection certificate when required)
- Signatures of inspectors and the manufacturer’s inspection seal
- Factory acceptance certificate
- Special materials and test documents as specified in the technical documentation (e.g., intergranular corrosion test, fire resistance test, oxygen valve, low-temperature valve, hydrogen sulfide resistance, low leakage, etc.)
█ Valve Body Marking
According to MSS SP25, the valve nameplate generally includes information about medium flow direction requirements, pressure end requirements, and for low-temperature valves, there should be corresponding clear markings on the valve body.
█ Valve Visual Inspection
The visual inspection of the valve considers factors such as the anti-corrosion condition of the valve assembly (including the actuator) paint, external defects of castings and forgings (cracks, shrinkage, looseness, sand holes, air holes, laminations, etc.), absence of foreign objects in the cavity (such as iron filings and dirt), and end face protection. The valves should generally be delivered in the following positions:
- Gate valves, globe valves, and similar valves should be in the fully closed position.
- Butterfly valves should be opened at 4°~5°.
- Plug valves and ball valves should be in the fully open position.
- Diaphragm valves should be in the closed position but not overly tightened.
- Check valve discs should be closed and secured (be sure to release the fixation before pressure testing).
█ Chemical Element Inspection
Verification of the main chemical element content of pressure-bearing components such as valve body, bonnet, stem, and connecting bolts made of alloy steel, stainless steel, various alloys (e.g., titanium alloy, copper alloy, nickel-based alloy, etc.) is carried out through spectral analysis. The inspection ratio should be based on technical requirements.
█ Valve Testing
Valve testing includes shell testing, sealing testing, and upper sealing testing. The test methods, test media, leakage requirements, etc., should strictly adhere to the corresponding category valve’s inspection standards or technical agreements. For valves with welding end connections in the CL900~CL2500 range, on-site pressure testing is not recommended. It is advised to conduct acceptance at the valve manufacturing factory. If on-site pressure testing is deemed necessary, appropriate tools and on-site protective measures should be prepared. For oxygen valves, construction sites typically do not have the conditions for pressure testing. It is recommended to conduct acceptance at the valve manufacturing factory.
Common Problems and Solutions for On-Site Acceptance Based on years of on-site valve acceptance experience in large-scale petrochemical projects, problems encountered during valve on-site acceptance have been summarized. Proposed solutions and responses are provided below, categorized by their level of importance.
█ Inconsistent Material
Chemical Composition of Valve Components On-site verification of critical valve components such as valve body, bonnet, stem, bolts, nuts, etc., should be conducted to analyze the main alloy elements specified in the material standard. In cases of non-compliance, acceptance is generally not recommended. Typically, there are no issues with the chemical composition of major pressure-bearing components like valve bodies and bonnets. However, externally purchased components like bolts and pressure caps often experience inconsistencies in material compared to buyer requirements. For instances of material substitution (using a higher-grade material in place of a lower-grade material), prior approval from the purchaser (or design unit) is required before execution.
█ On-Site Valve Pressure Testing Issues
Pressure testing is the most common and crucial issue encountered on-site, serving as the paramount criterion for evaluating valve quality. On-site valve pressure testing includes shell strength testing (at a pressure of 1.5 times the nominal pressure or the maximum allowable working pressure at 38°C), seal testing (at 1.1 times the nominal pressure), and safety valve adjustment testing. External leakage during shell strength testing is a common occurrence and is typically found at the connection between the valve body and bonnet, packing compression area, and pressure-bearing component defect areas. For certain mediums, external leakage requirements may be even stricter than internal leakage requirements, as direct discharge of the medium into the atmosphere can cause accidents or personal injuries. When external leakage occurs during on-site acceptance, inspectors should check gaskets and packing conditions at the corresponding locations. Pre-tightening bolts at the compression connection or replacing sealing gaskets and packing may be necessary. For cases where pressure-bearing component defects cause external leakage, the product should be returned and replaced, and the entire quality control process for that batch of products should be traced.
█ Valve Actuator and Operating Mechanism Issues
Valve drive units are generally categorized as gear, worm gear, chain wheel, pneumatic, hydraulic, electric, and mechanical interlock. Common problems occur during operation due to obstruction, chain detachment, incomplete switching, and remote control failures. During on-site inspections, inspectors should first check the engagement of rotating components, bearings, valve stems, and other transmission components. For electric, pneumatic, and hydraulic-driven valves, considerations should be given to wiring, pistons, hydraulic cylinders, air supply, etc., to ensure compliance with requirements. For valves with remote control capabilities unable to achieve proper switching, the valve manufacturer should be contacted for adjustments. In cases where valve stem bending renders the valve inoperable, the stem should be replaced, and the technical parameters of the new stem should be re-checked. Additionally, pressure testing and adjustments should be re-performed.
█ Valve Structural Length, End Connection Dimensions, Minimum Wall Thickness, Minimum Passage Size, and Appearance Issues
This mainly involves situations where the valve’s structural length, end connection dimensions, minimum passage size, and minimum wall thickness deviate from the specified technical standards set by the purchaser (excluding special non-standard products). In general, structural length, end face connection dimensions, valve minimum passage size, and minimum wall thickness should adhere to the technical standards specified by the purchaser. A certain proportion of valves of the same specification should be selected for checks on structural length, end connection dimensions, valve minimum wall thickness, and minimum passage size. Valves that exceed standard data (including tolerances, with wall thickness only considering positive tolerances) are generally not reparable on-site. Such valves can only be replaced.
█ Valve Entirety Anti-Corrosion, Paint Peeling, and Other Issues
This issue is commonly encountered during on-site acceptance inspections, especially in regions along the southeast coast where valves are heavily affected by climate and subjected to salt spray corrosion. Paint peeling is a severe issue. Both the manufacturing factory and on-site storage may have certain problems. In cases where paint peeling is severe, a visual inspection should be conducted to determine if on-site touch-up painting is necessary. If this problem is widespread across multiple products, it is recommended to return the products to the factory for treatment. The purchaser should review the manufacturer’s spray process, paint selection, and inspection processes to determine whether to continue using the products.
█ Valve Main Pressure-Bearing Components Exhibiting Defects
Inspection of the valve’s entire machine and the surface of cast and forged components of the valve body and bonnet should be visually examined. The external appearance quality of cast steel parts should comply with the B grade requirements of MSS SP-55 or JB/T 7927. If there are penetrative cracks, severe cold separation, honeycomb-like air holes, extensive areas of looseness, or defects that cannot be cleared, the product should be scrapped. For defects like scarring, folding, and slag inclusion that do not affect the minimum wall thickness and have a defect depth less than 10% of the design wall thickness, grinding and removal are acceptable. However, the remaining wall thickness after defect removal should not be less than the minimum wall thickness. For products with radiographic testing requirements, the evaluation of internal quality of castings should follow the provisions of ASME A16.34. Specific requirements should be in accordance with the technical specification book’s grade requirements.
█ Valve Nameplate and Body Marking Issues
Generally, the manufacturer’s name or trademark, valve model, nominal pressure, nominal size, valve body material, valve core, and valve seat material should be indicated on the valve body or nameplate. This complies with the requirements specified in the valve manufacturing standard and contract. However, issues like nameplate detachment or lack of markings may arise. If the nameplate has fallen off or does not meet requirements, the manufacturer should replace it. If the valve body marking is incomplete, the purchaser should use information provided by the manufacturer to check the foundry heat number (forging batch number), material, pressure, special equipment marking, etc., to trace the product’s entire quality control process. After confirming accuracy, it is recommended that the manufacturer supplements the valve body marking in a clear, indelible manner (such as through printing, engraving, or steel stamping). The marking should be affixed (printed, engraved, or stamped) in a clearly visible and neat manner.
In the petrochemical industry, valves play a critical role due to the variety, high procurement volume, and stringent technical requirements. Despite purchasers’ efforts to strengthen on-site inspections, numerous issues continue to arise during on-site acceptance and service.
♢ For valve suppliers, comprehensive quality process management in production is essential. This especially applies to material retesting, as it should not solely rely on factory pressure testing.
♢ For valve purchasers, it is crucial to request reasonable delivery cycles and reasonable procurement prices. Delivery cycles must align with the valve’s normal manufacturing and inspection period. The “lowest price” procurement approach should be avoided to ensure the quality of valves.
When quality issues arise during valve operation, whether for valve suppliers or end users, the consequences can be enormous and incalculable.