
1. Introduction to Large Riveted and Welded Components
Large riveted and welded components are the "skeleton" of industrial heavy equipment and infrastructure. The core lies in reasonable material selection (mainly low-alloy high-strength steel) and precision manufacturing (especially welding and assembly). Quality control runs throughout the process (material inspection, process control, non-destructive testing). Post-weld heat treatment and anti-corrosion treatment are key to ensuring long-term service reliability. The design must comprehensively consider strength, stiffness, fatigue, manufacturability, transportation and installation, and service environment. Understanding the material properties and complex process flow is crucial to ensuring product quality, performance, and service life.
2. Main Materials
Materials used for large riveted and welded components are usually selected for corrosion resistance, high temperature resistance, low temperature resistance, and commonly used steels.
Corrosion-resistant steels: 316/316L austenitic stainless steel, 2205 duplex stainless steel.
High-temperature steels (operating temperature > 350°C): 310S (0Cr25Ni20) austenitic heat-resistant stainless steel, Incoloy 800/800H high-alloy special heat-resistant steel.
Low-temperature steels (operating temperature < -20°C): 16MnDR low-temperature carbon manganese steel, nickel-based low-temperature steel, austenitic stainless steel.
Normal temperature steels (temperature -20°C ~ 350°C): Q235B carbon structural steel, Q355 series low-alloy high-strength steel (HSLA), Q355NH (Chinese standard) weathering steel.
3. Key Welding Process Steps
Pre-welding preparation: material cutting, forming, groove processing (precision control).
Thorough cleaning: oil, rust, water, scale, etc., on the groove and adjacent areas.
Assembly positioning weld: use the same welding materials and processes as formal welding to ensure positioning weld quality, with appropriate length and spacing. Check assembly gaps and misalignment.
Preheating (if needed): uniformly heat to the specified temperature and monitor and record.
Welding process:
Strictly follow the WPS and welding sequence.
Control interpass temperature (monitor and record).
For multi-layer and multi-pass welding, carefully clean interpass slag and spatter. Ensure good fusion of weld beads and avoid defects.
Monitor key parameters (current, voltage, speed, gas flow, etc.).
Welding Techniques |
Application Scenarios |
Cutting processes used |
Flame cutting (CNC cutting), plasma cutting, laser cutting, shearing, sawing. High-precision groove processing (such as milling edges, groove cutting machines). |
Forming processes used |
Plate rolling (cylinders, cones), bending (press brake), pressure forming (large press), rolling. |
Assembly and fitting |
Use large tooling fixtures and platforms (such as welding positioners, roller racks) to ensure precise position and dimensions of each part. This is a key quality control step. |
Common Welding Methods |
Application Scenarios |
Submerged Arc Welding |
Suitable for long straight welds and circumferential welds (such as cylinder longitudinal and circumferential seams). |
Gas Shielded Welding |
MAG (CO2 or mixed gas), MIG (inert gas). The most widely used, highly flexible (manual, semi-automatic, automatic), suitable for various positions and joint types. |
Shielded Metal Arc Welding (SMAW) |
Suitable for positions difficult to automate, short welds, and repair welding. Lower efficiency, relies on welder skill. |
Electroslag Welding |
Used for vertical welding of ultra-thick plates (such as box beam diaphragms). |
Narrow Gap Welding |
Used for butt welding of ultra-thick plates, high efficiency, minimal deformation. |
Post-weld Treatment |
|
Stress Relief |
Large components generally require overall or local post-weld heat treatment (usually stress relief annealing), removal of slag and spatter, grinding of welds and surrounding areas to release residual welding stress, prevent deformation and cracking, and improve toughness. |
Straightening |
Flame straightening, mechanical straightening (press, jack) to control welding deformation. |
Machining |
Precision machining such as milling, boring, drilling on key mating surfaces and hole positions. |
We conduct non-destructive testing and inspection of products:
Item | Content |
Visual Inspection | Surface defects (cracks, undercut appearance inspection (VT), porosity, arc pits, etc.). |
Ultrasonic Testing (UT) |
Detect internal defects (lack of fusion, lack of penetration, slag inclusion, cracks, etc.), especially important for thick plates. |
Radiographic Testing (RT) |
Directly displays internal defects, commonly used for important butt joints. |
Magnetic Particle Testing (MT) |
Detect surface and near-surface defects (ferromagnetic materials). |
Penetrant Testing (PT) |
Detect surface open defects (non-ferromagnetic materials). |
Destructive Testing (Sampling) |
Such as tensile, bending, impact, hardness, metallography, etc. (usually conducted during process evaluation or spot checks). |
Dimensional Inspection |
Check whether the overall structural dimensions and key part dimensions meet the drawing requirements. |
Pressure/Leakage Test (if needed) |
Such as hydraulic test, pneumatic test, airtightness test. |
4. Typical Application Scenarios
Industry |
Product Cases |
Key Solutions |
Mining Machinery |
Crusher frames, ball mill drums, mining truck chassis, kiln bodies, furnace bodies, etc. |
Impact-resistant structural design + localized reinforced welding |
Energy Equipment |
Wind power tower (diameter Φ4.5m), hydropower station pressure steel pipes |
Circumferential automatic welding + 100% radiographic inspection |
Engineering Ships |
Dredger cutter frames, port crane booms |
Salt spray environment anti-corrosion welding (C5-M level protection) |
Chemical Equipment |
Reactor shells (thickness ≥80mm), hydrogenation reactors |
High temperature and high pressure resistant welding (PED 2014/68/EU certification) |
5. Quality Assurance System
1. Certification Standards:
① EN 1090-2 EXC3 (Highest grade of steel structure in the EU)
② ASME Section VIII Div.1 (Pressure Vessel Code)
③ ISO 3834-2 (Welding Quality Management System)
Material-specific Standards:
① ISO 15614 "Specification and Qualification of Welding Procedures for Metallic Materials" series standards (e.g., ISO 15614-1 for steel arc welding, -8 for pipe welding, etc.) support filler material compatibility tests and process parameter verification.
② GB/T 19867.1 "Welding Procedure Specification and Qualification" (Chinese National Standard) equivalent to ISO 15614, mandatory for domestic projects with clear requirements for WPS preparation and qualification test methods.
3. Inspection and Defect Acceptance Standards:
① ISO 5817 "Quality Levels for Imperfections in Welds in Steel, Nickel, Titanium and Their Alloys"
② GB/T 11345 "Manual Ultrasonic Testing Method and Acceptance Levels for Steel Welds" (Chinese National Standard)
Core Standards for Nondestructive Testing (UT) of Large Structures
Note: Large riveted and welded parts often involve dissimilar steel welding (e.g., Q355B with 316L), requiring additional compliance with ISO 18274 (Nickel-based filler metal standard) or AWS A5.11 (Stainless steel electrode specification).
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