What are the common defects in tank fabrication and how to avoid them?

Tank fabrication involves multiple complex processes, and improper operation or inadequate control in any link may lead to quality defects. Understanding common defects and corresponding avoidance measures is crucial to ensuring the safety, durability and performance of tanks. The following summarizes the most common defects in tank fabrication and practical prevention methods.

1. Material Defects

Defect Performance: Common material defects include surface rust, cracks, scratches, uneven thickness, and unqualified mechanical properties. In some cases, the material specification may not match the design requirements, which directly affects the structural strength of the tank.

Avoidance Measures: Strictly select steel materials that comply with national and industrial standards (such as AWS D1.1, GB 50205-2020) and design drawings. All materials must be accompanied by complete quality certificates, including material composition, mechanical properties and inspection reports, with traceable batch numbers for quality tracking. Before processing, conduct a comprehensive inspection: check the appearance for rust, cracks and scratches, verify dimensional accuracy and thickness uniformity, and conduct sampling inspection of mechanical properties and chemical composition for key materials to reject unqualified materials.

2. Cutting and Blanking Defects

Defect Performance: These defects mainly manifest as uneven cutting surfaces, burrs, oxide scales, and cracks on the cutting edge. In addition, dimensional deviation exceeding the allowable range and irregular bevel shape (for welding) are also common, which affect subsequent assembly and welding quality.

Avoidance Measures: Select the appropriate cutting method (flame cutting, plasma cutting, mechanical cutting) according to the material type and thickness. Regularly calibrate cutting equipment to ensure processing precision. Train operators to standardize operations, including adjusting cutting parameters and cleaning the cutting surface in time. After cutting, immediately inspect the cutting surface and dimensions; rework unqualified parts promptly to avoid affecting subsequent processes.

3. Welding Defects (Most Common)

Defect Performance: Welding is the core link of tank fabrication, and its defects are the main hidden dangers affecting tank safety. Common welding defects include pores, slag inclusion, incomplete fusion, cracks, undercut, excessive weld reinforcement, and uneven weld seams. These defects reduce the bearing capacity of the weld and may lead to leakage or structural failure.

Avoidance Measures: Ensure welders hold valid qualification certificates and strictly implement the approved Welding Procedure Specification (WPS). Dry welding materials (welding rods, wires, fluxes) according to requirements to prevent moisture absorption, which can cause pores. Strictly control welding parameters (current, voltage, welding speed, interpass temperature) to avoid defects. Conduct visual inspection and non-destructive testing (ultrasonic, radiographic testing) after welding; handle unqualified welds in a timely manner. For key welds, perform post-weld heat treatment to eliminate internal stress and improve welding quality.

4. Forming and Assembling Defects

Defect Performance: Forming defects include deformation of components after stamping or rolling, such as tank body ovality, irregular head shape, and uneven wall thickness. Assembling defects mainly include inaccurate positioning, excessive gaps between components, and poor fit of connecting parts, which affect the overall structure and sealing performance of the tank.

Avoidance Measures: Follow design drawings to carry out forming processes, and use professional forming equipment that is regularly calibrated. Adopt precise positioning tools (such as positioning jigs) during assembly to control component gaps and avoid assembly deviation. After forming and assembling, inspect the shape, size and assembly accuracy of the tank; correct deformation or adjust positioning in time to ensure indicators such as roundness and straightness meet requirements.

5. Surface and Corrosion Defects

Defect Performance: These defects occur in the finishing stage, including surface rust, scratches, and paint peeling after anti-corrosion treatment. Insufficient anti-corrosion coating thickness or missing coating will reduce the tank’s corrosion resistance and shorten its service life.

Avoidance Measures: Conduct thorough derusting before painting to ensure the surface is clean and dry. Select anti-corrosion coatings suitable for the use environment (such as anti-corrosion coatings for chemical tanks) and standardize the painting process to ensure uniform coating thickness and no missing coating. Avoid scratches during component handling and packaging. Take anti-corrosion protection measures during storage and transportation to prevent rust.

6. Dimensional and Shape Defects

Defect Performance: The overall dimensions of the tank (such as length, diameter), roundness, straightness, and wall thickness exceed the allowable range of the specification. These defects affect the tank’s installation and use, and may reduce its structural stability.

Avoidance Measures: Strictly follow design drawings for processing and regularly calibrate processing equipment (rolling machines, bending machines) to ensure precision. Use professional measuring tools (such as tape measures, level gauges) to conduct dimensional inspection at each key process. If deviations are found, adjust the processing parameters or equipment in time to ensure all indicators meet the standard.