Quality control of WFGD anti-corrosion project

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(1) Inspection of raw materials upon arrival. The variety, quality, and shelf life of raw materials are key aspects in the incoming inspection. The acceptance criteria for rubber sheets include variety, thickness, hardness, electrical spark testing (to check for holes), and appearance. The storage temperature for the raw materials of glass flake should be below 20°C, with the relative humidity kept below 75%. (2) Quality control in the preprocessing process. The pre-treatment in anti-corrosion construction mainly includes patch welding and grinding of the substrate, as well as grinding of the rubber sheets in rubber lining installation. For the installation of rubber linings and glass flake coatings, the cleanliness of the substrate surface after sandblasting must reach Sa2(1/2) level, with roughness values of 50μm and 70μm respectively. Sandblasting quality is a mandatory inspection item; the sandblasted surfaces of various areas are inspected based on the standard samples for sandblasting quality. At the same time, strict monitoring is carried out on the quality of the compressed air used for sandblasting as well as the quality of the sand; oil and moisture in the compressed air are strictly prohibited. (3) Control of construction environmental conditions: At the construction site for the lining rubber and glass flake material, the temperature should be maintained between 10 and 35°C, while the relative humidity should be kept below 60%. (4) Construction process control 1) Material preparation. These include anti-corrosion materials such as rubber-lined primers, adhesives, glass flake primers, glass flake resins, fiberglass epoxy resins, epoxy paints, acid-resistant mortars, and brick-laying mortars, which need to be prepared on-site during construction. The ingredient preparation process mainly involves monitoring the accuracy of the ratios and the activation period. 2) Process coordination. For anti-corrosion treatment, the first and second coats of primer must be applied within 24 hours after sandblasting. There are specified minimum and maximum time intervals between the primer and the first coat of adhesive, between the two coats of adhesive, and between the second coat of adhesive and the adhesive-coated sheets. During construction, strict supervision and inspection of the time intervals for each process must be carried out in accordance with the process documents, to ensure that the sequence of processes meets the specified requirements. 3) Gasket lapping. The overlapping direction of the basic principle should be consistent with the flow direction of the medium, in order to prevent the medium from eroding the overlap seam of the adhesive sheet. The construction workers must determine the overlapping pattern of the rubber sheets based on the flow direction of the media in various parts of the equipment. During construction, the overlapping areas of the adhesive sheets must be carefully inspected to ensure the correct direction of the joints. 4) Lining rubber. The quality inspection items for the rubber lining of absorption towers and various tanks include: thickness, hardness, spark testing, appearance, and adhesion strength. Among these, thickness, hardness, electrical spark testing (no leakage at a specified voltage of 14 kV for 100% inspection), and visual inspection are carried out on the in-process products, while peel strength testing (specified value ≥ 4 N/mm) is conducted on product test samples. Visual inspection requirements: The direction of the overlaps is correct, with no cross-over joints; the type of rubber gasket used in each area meets the specified standards, and no serious defects such as bubbles, bulges, or large cracks are observed. 5) Glass flake resin lining coating. The quality acceptance criteria for glass flake coatings include: thickness, hardness, spark test, appearance, and adhesion strength. Regarding the thickness requirements: Before inspection, calibrate the thickness gauge using its standard plate to determine the thickness of the scale lining; use the thickness gauge to check 2–3 locations every 4 m2. Appearance requirements: 100% spark testing must be conducted on the scale-lined surfaces at a voltage of 4 kV/mm, to ensure no leakage of electricity; during testing, it is necessary to avoid excessively high voltages or prolonged exposure to the same area, and the voltage must remain stable. The tester should be used to scan all lined surfaces at a scanning speed of 300–500 mm/s. Check for any defects. Check the hardness (Brinell hardness, specified value 40) and bonding strength (specified value 7 MPa) on the product test plates. (5) Inspection of the flue gas desulfurization system after trial operation: Based on experience, most quality issues related to the anti-corrosion coating become apparent within the first year of operation; therefore, a thorough inspection of the anti-corrosion coating is necessary after the trial operation to check for cracks, bulging, peeling, or any other signs of damage. It is recommended to focus on checking the following areas. 1) Rubber lining layer at the spray section of the absorption tower. The key areas are the 1–2 meter section below the spray layer and the locations of the spray branch pipe brackets; these areas are lined with a double layer of rubber, are subject to the most severe erosion, and are most prone to problems. 2) Anti-corrosion coating at the raw tobacco inlet of the absorption tower. The media in contact with this area include flue gas, slurry, and various vaporized media, with large temperature fluctuations. Anti-corrosion measures such as rubber sheets, glass flake coatings, and acid-resistant tiles are generally used, and this area must be carefully inspected after trial operation. 3) Rubber lining layer at the connection point of the stirrer blades. The agitators for tanks and pits have blades that are installed on-site, with the joints sealed with rubber at the site; due to their complex shape and numerous overlapping seams, the blades are prone to cracking as a result of impact from the medium during operation.