Production Process Quality Control

I. Technical Control

Familiarize with design drawings, carefully review and make records, promptly contact the design unit for written replies upon discovering issues. Prepare construction organization design, construction plans, welding processes, and welding quality management guidelines. Ensure adequate pre-construction preparations. Develop material budgets, prepare material procurement plans, conduct layout sizing, and procure materials based on the sizing.

Draw detailed drawings for further design; create part drawings, unit component drawings, and trial assembly drawings according to process requirements. Additionally, create process flowcharts covering the entire process from parts to unit components to segment units, including cutting, assembly, welding, and trial assembly. Organize technical personnel and workers to conduct technical and quality briefings for key processes, techniques, and locations.

II. Material Quality Control

The processing and manufacturing of steel structures is the core link in the entire construction process, directly determining the applicability and structural performance of the steel structure. Therefore, strict control is required from material inspection to the final coating application. During material inspection, verify the selected models, specifications, and material quality. Once materials meet requirements, proceed with setting out and cutting. During setting out and marking, clearly indicate assembly marks, bolt hole markings, stiffener positions and directions, tilt marks, centerlines, baselines, and inspection lines. If necessary, create templates. Before marking, correct any bends or deformations in the material. Prior to cutting, thoroughly clean the cutting surface of rust and dirt. After cutting, promptly remove slag and spatter, strictly control cutting errors, and eliminate surface cracks and delamination.

III. Setting Out and Cutting Quality Control

The quality of setting out and cutting directly impacts subsequent processes, potentially leading to the scrapping of all parts. Therefore, strict quality monitoring during this process is crucial. Common quality issues include severe deformation of long and thin parts, uneven cutting surfaces due to cutting gas or material impurities, oversized parts due to overlooking post-process shrinkage, and batch scrap due to incorrect process documentation. Common quality control measures include:

Strengthen process monitoring, strictly implement the "three-inspection system" (operator self-inspection, mutual inspection by team leaders, and special inspection by quality inspectors), keep process records, and ensure the system is not merely a formality.

Conduct spot checks before batch part setting out to avoid irreparable issues. For complex part templates, adopt a supervision and inspection system to address issues before cutting.

Maximize the use of automatic and semi-automatic processes to reduce manual operations and minimize human error.

IV. Welding Quality Control

Welders must be certified and operate within their certified scope. Unauthorized personnel are prohibited from welding.

Welding materials must be dried according to regulations and stored in insulated containers for easy access.

Before welding, thoroughly clean the interface area within 50mm of both sides, remove rust, oil, and other impurities. Inspect the assembly quality. If unsatisfactory, repair or adjust before welding. After welding, promptly remove weld spatter and stamp the welder's mark near the weld.

For multi-layer welding, perform continuous welding and promptly remove slag after each layer. If defects are found, use carbon arc gouging to thoroughly remove the defective area, grind clean the decarburized layer, and re-weld.

If weld cracks occur, welders are prohibited from unauthorized repairs. Report to the technical director for investigation, determine the cause, and develop a repair plan. The same location should not be repaired more than twice.

Strictly prohibit striking arcs on the base metal outside the weld area.

Submerged arc welding is preferred for plate jointing and H-beam main welds.

When welding T-joints and butt joints, install lead-in and lead-out plates at both ends. Start and stop welding on these plates to ensure weld quality as voltage and current are unstable during arc striking and extinguishing.

For welds with quality grades 1 and 2, the quality department must strictly monitor the welding process and assign dedicated personnel to perform ultrasonic flaw detection to ensure the welds meet design requirements.

Post-weld deformation correction can be achieved through mechanical straightening or flame straightening. When using flame straightening, heating the same area should not exceed twice, and the temperature should not exceed 900°C. When manual hammering is used, take measures to prevent dents and damage to the base metal. Q345 steel should not be water-cooled after flame straightening.

For components with significant deformation, apply anti-deformation measures before welding, select a reasonable welding sequence to minimize deformation. For plates less than 8mm thick, prioritize the use of CO2 gas shielded welding to reduce deformation.

V. Anti-Corrosion Quality Control

Raw material or component inspection: Ensure raw materials or components are qualified and visually meet standards, with no cracks, severe rust, or other defects.

Component or raw material derusting: The derusting method and grade of component surfaces must comply with design drawings or specifications. For example, Sa2 grade refers to industrial spray derusting, removing loose oxide scales, loose rust, and other contaminants. Welding spatters and slag must be thoroughly cleaned. Sa2.5 grade refers to near-white spray derusting, leaving only slight spots or stripes on the metal surface. The surface should be cleaned with compressed air or other tools, appearing silver-gray.

Paint Application

The type, name, color, and expiration date of the paint must match the quality certificate and product qualification certificate. There should be no signs of skinning, caking, gelling, etc. Before painting, the site supervisor must inspect the rust removal of the components, and only proceed to the next construction step if the requirements are met. During painting, attention should be paid to the construction temperature, and the paint film should be fully dried. Ensure the time interval between each coat of paint, and the paint film must be naturally dried for 7 days before use. Painting should not be performed outdoors during windy, sandy, rainy, foggy, or snowy weather.

During paint application, quality inspections should be conducted after each coat. If defects or damage such as pinholes, bubbles, sagging, or missed areas are found in the coating, remedial measures must be taken before the next coat of paint. The following provisions should be followed: If the paint film has defects such as missed areas or pinholes, directly apply another coat; if there are bubbles or sagging, remove that portion of the coating and repaint.

The number of paint coats and the paint film thickness should comply with design and specification requirements. If no requirements are specified, at least 3 coats of paint should be applied. The paint film thickness should be 150μm for outdoor applications and 125μm for indoor applications, with an allowable deviation of ±25μm. The allowable deviation for the dry paint film thickness of each coat is ±5μm. After painting, the component surface should have no incorrect or missed painting, and the coating should be free from peeling and rusting. The coating should be uniform, with no obvious wrinkles, sagging, pinholes, or bubbles. The total paint film thickness should not be less than 0.2mm.

After each coat of paint, the site supervisor should inspect the paint film thickness and adhesion. Instruments for paint film thickness measurement: coating thickness gauge; method for paint film adhesion testing: cross-cut test.

Ⅵ. Finished Product Control

The finished product storage yard should be flat and have a good drainage system. Components should be raised 300 mm from the ground to prevent rainwater and mud from adhering to them. Protective measures should be taken during the handling and stacking of finished components to prevent damage to the coating quality. Do not walk or step on the components, as this could damage the coating. Packaging should be done after the coating has dried, and measures should be taken to protect the coating from damage. If the coating is damaged during transportation or installation, timely repairs should be made. Reinforcement measures should be taken during the transportation of components to prevent deformation and damage.

In summary, quality control in steel structure fabrication is a systematic project, and the quality of each process will affect the overall quality of the project. Only by satisfying the quality control requirements of each process can the quality control objectives be achieved, and qualified steel structural components produced to meet the specifications and requirements of the owner.