I. Introduction to Large-Scale Riveted and Welded Components
Large riveted and welded components serve as the "skeleton" of industrial heavy-duty equipment and infrastructure. At their core lie the judicious selection of materials—primarily low-alloy high-strength steel—and precision manufacturing, particularly in welding and assembly. Quality control is rigorously implemented throughout the entire process, including material inspection, process monitoring, and non-destructive testing. Post-weld heat treatment and anti-corrosion treatments are critical to ensuring long-term reliability under service conditions. Moreover, design must comprehensively account for factors such as strength, stiffness, fatigue resistance, manufacturability, transportation and installation requirements, as well as the specific environmental conditions the components will face. A thorough understanding of the material properties and the intricate manufacturing processes is essential for guaranteeing product quality, performance, and durability.
II. Main Materials
Materials commonly used for large riveted and welded components typically include steels that are core-resistant to corrosion, high temperatures, and low temperatures—and are also the most widely used.
Corrosion-resistant steels: 316/316L austenitic stainless steel, 2205 duplex stainless steel
High-temperature-resistant steels (operating temperature > 350°C): 310S (0Cr25Ni20) austenitic heat-resistant stainless steel, Incoloy 800/800H high-alloy special heat-resistant steel
Low-temperature-resistant steels (operating temperature < -20°C): 16MnDR low-temperature carbon-manganese steel, nickel-based low-temperature steel, and austenitic stainless steel
Room-temperature steels (temperature range: -20°C to 350°C): Q235B carbon structural steel, Q355 series low-alloy high-strength steel (HSLA), and Q355NH (national standard) weathering steel.
III. Key Processes in Welding Technology
Pre-weld preparation: Material cutting, forming, and beveling (with precision control).
Strict cleaning: Remove oil, rust, water, oxide scale, and other contaminants from the bevel and surrounding areas.
Assembly tack welding: Use the same welding materials and processes as for the final welds to ensure high-quality tack welds of appropriate length and spacing. Also, inspect assembly gaps and misalignment.
Preheating (if required): Heat evenly to the specified temperature and monitor and record accordingly.
Welding process:
Weld strictly according to the WPS and welding sequence.
Control interlayer temperature (monitor and record).
When performing multi-pass, multi-layer welding, carefully clean away interlayer slag and spatter. Ensure proper fusion of each weld pass to prevent defects.
Monitor key parameters (current, voltage, speed, gas flow rate, etc.).
Welding Process |
Application scenarios |
Material preparation process |
Flame cutting (CNC cutting), plasma cutting, laser cutting, shearing, and sawing. High-precision bevel machining (such as edge milling and bevel cutting machines). |
Forming process adopted |
Rolling (cylindrical and conical shapes), bending (using a bending machine), pressure forming (with large-scale presses), and roll forming. |
Assembly and Alignment |
Using large-scale tooling fixtures and platforms—such as welding positioners and roller stands—ensures the precise positioning and dimensions of each component. This is a critical step in quality control. |
Common Welding Methods |
Application scenarios |
Submerged Arc Welding |
Suitable for long straight welds and circumferential seams (such as longitudinal and circumferential seams of cylindrical shells). |
Gas-shielded welding |
MAG (CO2 or mixed gas), MIG (inert gas). Widely used and highly versatile (manual, semi-automatic, automatic), suitable for various positions and joint types. |
Shielded Metal Arc Welding |
Suitable for positions that are difficult to automate, short welds, and repair welding. It is less efficient and relies heavily on the welder's skill. |
Electroslag Welding |
Vertical welding for extra-thick plates (e.g., box-beam diaphragms). |
Narrow-Gap Welding |
Designed for butt welding of ultra-thick plates, it offers high efficiency and minimal deformation. |
Post-weld treatment |
|
Stress Relief |
Large components generally require post-weld heat treatment—either overall or localized (typically stress-relief annealing)—to remove weld slag and spatter, followed by grinding of the weld seam and its surrounding area. This process helps relieve residual welding stresses, preventing deformation, cracking, and enhancing the material's toughness. |
Orthopedic |
Flame straightening and mechanical correction (using presses and jacks) are employed to control welding deformation. |
Mechanical Processing |
Perform precision machining operations such as milling, boring, and drilling on critical mating surfaces and hole locations. |
We will conduct non-destructive testing, inspection, and testing on the products:
| Project | Content |
Visual Inspection |
Surface defects (cracks, undercut appearance inspection (VT), porosity, arc craters, etc.). |
Ultrasonic Testing (UT) |
Detecting internal defects (such as lack of fusion, incomplete penetration, slag inclusions, and cracks) is especially critical for thick plates. |
Radiographic Testing (RT) |
Intuitively displays internal defects and is commonly used for critical butt joints. |
Magnetic Particle Testing (MT) |
Detection of Surface and Near-Surface Defects (Ferromagnetic Materials) |
Penetrant Testing (PT) |
Detecting surface opening defects (non-magnetic materials). |
Destructive Testing (Sampling) |
Such as tensile testing, bending tests, impact tests, hardness tests, and metallographic analysis (typically conducted during process qualification or random inspections). |
Dimensional Inspection |
Check whether the overall structural dimensions and dimensions of key components meet the drawing requirements. |
Pressure/Leak Test (if required) |
Such as hydraulic tests, pneumatic tests, and air-tightness tests. |
IV. Typical Application Scenarios
Industry |
Product Cases |
Key Solutions |
Mining machinery |
Crusher frame, ball mill drum, mine car chassis, kiln body, furnace body, and more |
Impact-resistant structural design + locally reinforced welding |
Energy Equipment |
Wind turbine tower sections (diameter Φ4.5m), hydropower station pressure steel pipes |
Automatic circumferential welding + 100% radiographic inspection |
Engineering Vessels |
Dredger cutterhead frame, port crane boom |
Salt Spray Environment-Resistant Welding (C5-M Level Protection) |
Chemical equipment |
Reactor vessel shell (thickness ≥ 80 mm), hydrogenation reactor |
High-Temperature and High-Pressure Welding (PED 2014/68/EU Certified) |
V. Quality Assurance System
1. Certification Standards:
① EN 1090-2 EXC3 (EU's highest-grade steel structure)
②ASME Section VIII Div.1 (Pressure Vessel Code)
③ISO 3834-2 (Welding Quality Management System)
Specialized material standards:
① The ISO 15614 series of standards, "Welding Procedure Specifications and Qualification for Metallic Materials" (e.g., ISO 15614-1 for steel arc welding, -8 for pipe welding, etc.), supports weld material compatibility testing and verification of process parameters.
②GB/T 19867.1 "Welding Procedure Specifications and Assessment" (China National Standard) is equivalent to ISO 15614, mandating the preparation of detailed Process Specification Sheets (WPS) and specifying clear requirements for assessment test methods in domestic projects.
3. Inspection and Defect Acceptance Criteria:
① ISO 5817 "Quality Grades for Defects in Fusion Welded Joints of Steel, Nickel, Titanium and Their Alloys"
② GB/T 11345 "Manual Ultrasonic Testing Methods and Acceptance Criteria for Steel Welds" (China National Standard)
Core Standard for Nondestructive Testing (UT) of Large Structures
Note: Large riveted and welded components often involve dissimilar steel welding (e.g., Q355B with 316L), requiring additional compliance with ISO 18274 (the nickel-based welding consumables standard) or AWS A5.11 (the stainless steel electrode specification).
Keywords
Large Riveted and Welded Components
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