Chemical prefabricated welded components are assemblies or modules manufactured in a factory workshop according to construction drawings, through processes such as cutting and forming, beveling, fit-up and welding, inspection and pressure testing of pipes, profiles, and steel plates, then transported to the site for integral hoisting and assembly. Compared with on-site piece-by-piece construction, factory prefabrication can shorten on-site construction time by 30%~50%, provide more stable weld quality, and is less affected by weather. It is widely used in petroleum, chemical, natural gas, coal chemical, nuclear power, municipal pipeline networks, and other facilities.
II. Main Product Categories
Table
| Category | Typical Form | Application Scenario |
|---|---|---|
| Pipe Spool Prefabricated Components | Straight pipe + elbow + tee + flange welded pipe rack | Process piping, utility piping |
| Steel Structure Welded Modules | Pipe rack supports, equipment frames, operating platforms, equipment bases | Plant pipe racks, steel structure frames |
| Pressure Vessel Components | Cylinder shells, heads, nozzle flanges, manholes, reinforcing rings | Reactors, heat exchangers, storage tanks, towers |
| Non-standard Equipment Shells | Silos, chimneys, flues, equipment enclosures | Environmental protection, storage and transportation, auxiliary systems |
III. Commonly Used Materials
- Carbon Steel: Q235B, Q355B (Q345B), 20# seamless pipe, Q345R vessel plate
- Stainless Steel: 304/304L, 316/316L, 321, 310S
- Alloy Steel: 15CrMo, 12Cr1MoV, P91/P22 (high-temperature and high-pressure service)
- Clad Plate: Stainless steel + carbon steel explosion-bonded clad plate (corrosion resistance + pressure-bearing economy)
IV. Manufacturing Process and Technical Parameters
Table
| Item | Content |
|---|---|
| Welding Method | GTAW argon arc welding (root pass), SMAW manual arc welding, FCAW flux-cored gas-shielded welding, SAW submerged arc automatic welding |
| Beveling | Machining / flame cutting, V-type, double V-type or U-type bevel, root face and angle per WPS |
| Welder Qualification | Certified welders, working per NB/T 47014 Welding Procedure Qualification (PQR) + Welding Procedure Specification (WPS) |
| Non-destructive Testing | RT radiographic, UT ultrasonic, MT magnetic particle, PT penetrant; pressure-containing welds generally Grade II acceptance per design requirements |
| Surface Treatment | Sandblasting to Sa2.5 grade, anti-rust primer + topcoat; stainless steel parts pickled and passivated |
| Size Range | Piping DN15 ~ DN1200; plate thickness 3 ~ 80 mm; single module up to tens of tons |
| Design Parameters | Design pressure vacuum ~ 42 MPa; design temperature -196 ℃ ~ 600 ℃ (depending on material grade) |
| Flange Standards | GB/T 9119, HG/T 20592, SH/T 3406, ANSI B16.5, JIS B2220 |
| Applicable Standards | GB 50235 "Code for Construction of Industrial Metallic Piping", GB 50236 "Code for Construction of Field Equipment, Industrial Pipe Welding Engineering", GB 150 "Pressure Vessels", NB/T 47014 |
V. Quality Control Key Points
- Material Traceability: Base materials and welding consumables all have material certificates, with transferred identification numbers traceable throughout the entire process.
- Pre-weld Preheating / Interpass Temperature: Alloy steel and thick plates preheated per WPS, interpass temperature controlled.
- Weld Inspection: 100% visual inspection + proportional RT/UT, stainless steel additionally subjected to PT dye penetrant testing.
- Pressure Testing: Pressure-containing components subjected to hydrostatic / pneumatic testing before delivery per design (per drawing requirements).
- Document Delivery: As-built documentation includes material certificates, welding records, heat treatment records, NDT reports, pressure test records, as-built drawings.
