The iron shell modification and maintenance units for glass-lined pressure vessels should obtain the corresponding modification and maintenance license. Specific requirements should be implemented in accordance with Section 5 of the TSGR0004-2009 "Safety Supervision Regulations for Fixed Pressure Vessels."
2 Patching of Local Ceramic Burst in Glass Lining Reactor of the Fritted Glass Equipment
2.1 Local porcelain repair on the glass-lined reactors in glass-lined equipment involves applying a corrosion-resistant coating over the damaged porcelain surface. The repair layer must meet the following requirements: it should not affect the reaction of the medium inside the equipment and should comply with the reaction process requirements. Methods include: corrosion-resistant metal packing, corrosion-resistant metal sheet repair, coating repair, PTFE sleeve repair, and thermal spraying ceramic powder repair, among others. If it is necessary to enter the glass-lined tank for repair, the following work must be done:
Comprehensively clean the reaction vessel to prevent the hazards posed by gases and remaining materials generated from the decomposition of materials to human health.
(2) Close all incoming material valves and disconnect them from the incoming material pipes, adding blind plates to prevent material from entering the tank during filling.
(3) Disconnect the power to the motor that drives the stirrer and assign a dedicated person to supervise, or remove the V-belt. This is to prevent accidental re-energizing of the stirrer, which could injure personnel operating inside the tank.
(4) Measure and replace the air inside the tank with non-flammable and non-toxic gases to prevent residual hazards from remaining in the reaction tank that could harm humans. In case of necessity, enter the tank wearing a respirator and ensure forced ventilation.
Tank entry construction requires constant supervision by a guardian, with the entrants wearing safety belts. In case of any adverse symptoms, the guardian must immediately pull the tank entry personnel out.
(6) Always wear protective eyewear during polishing and avoid the front of the repair area to prevent the glass frit from shattering and damaging the eyes and face.
(7) Prior to repair, any perforations or corrosion pits in the pot wall must be welded; operators performing the repair on the iron mold must possess the relevant qualifications for welding pressure vessels.
(8) During welding, it is necessary to protect the porcelain surface outside the welding area to prevent the porcelain from being damaged by weld slag. Additionally, welding should be intermittent; if the iron substrate temperature is found to be high, stop immediately and wait for the welding area to cool before resuming welding to prevent the porcelain layer from cracking due to excessive temperature. After welding, use an angle grinder to smooth the welded area, and then perform a hydrostatic test according to the technical parameters specified in the completion drawings. The weld area is considered passable if it does not leak. The equipment should be left undisturbed for one day after welding repairs to release welding stress.
2.2 Corrosion-Resistant Metal Filling Method: When there are micro-pores in the glaze surface of glass-lined equipment, it is often possible to use corrosion-resistant metals like gold and tantalum to make plugs that can be directly inserted into the small holes. The advantages of this repair method are: due to the sufficient stability of corrosion-resistant metals against certain media, the lifespan is longer if used appropriately. The disadvantages include: high cost, limited repair area, suitability only for small hole repairs, complex construction techniques, and the risk of plug detachment and leakage if the repair technique is not up to par. Some media are not suitable, such as gold against aqua regia, bromic acid, iodic acid, and nitric acid mixtures, alkaline cyanides and sulfides, and instability against chlorine, bromine, and iodine. Tantalum is used to repair equipment that is not resistant to fuming sulfuric acid. Additionally, if the equipment contains lead, zirconium, or stainless steel components, it can also cause corrosion of tantalum. Moreover, alkalis can promote the embrittlement of tantalum, and as temperatures rise, its erosion rate increases. Currently, the corrosion-resistant metal filling method is rarely used for on-site repairs.
2.3 Corrosion-Resistant Metal Sheet Repair Method: Primarily, use corrosion-resistant metal sheets that can withstand the medium in question to cover the locally damaged areas of the porcelain surface, then secure them tightly with screws made from the same metal. Specific methods are illustrated in Figure 1. Corrosion-resistant metal materials include S31608 (06Cr17Ni12NO2), S31603 (022Cr17Ni12MO2), and S31668 (06Cr17Ni12MO2Ti).
2.4 Coating Repair Method: This method involves applying corrosion-resistant coatings over the damaged surface. Its characteristics are: simplicity. It can repair various shapes of damaged ceramic surfaces with good corrosion resistance. Disadvantages: The quality of application significantly affects the service life, and different coatings should be chosen for different media. The following are the repair requirements for several types of coatings:
Bellzona: Import repair coatings, product name BELZONA 1311 (Ceramic-R-Metal) is used for repairing metal systems damaged by chemical corrosion (suitable for repairing localized porcelain cracks in enamel equipment). The manufacturer, Bellzona DNC 1311, blends high molecular weight reactive polymers with silicon steel alloys to form a repair system consisting of two raw materials. This system, specially designed, is used for repairing damaged metal and has anti-chemical corrosion properties. The material is non-machinable and can only be ground. After full curing during the repair process, the application includes: carbonic acid, 10% hydrobromic acid, 10% nitric acid, 5% phosphoric acid, etc. Refer to the Bellzona product manual for specific usage instructions.
Inorganic Paint Repair: This involves mixing binder fillers with a certain amount of hardening accelerators, primarily using acid-resistant mortar. Its characteristics include resistance to both concentrated and dilute inorganic and organic acids, fatty acids, aqua regia, mixed acids, as well as organic solvents like alcohols, ketones, and fats. It also withstands halogen (except F) acidic and neutral salt solutions, but is not resistant to alkaline or alternating acidic-alkaline mediums. The acid-resistant mortar component binder: water glass with fillers such as acid-resistant ash, green basalt powder, diatomite, quartz powder, ceramic powder, and barium sulfate, etc. When water glass is mixed into mortar, its proportion is about 27-30% of the total material weight, while for slurry, it is 40-50%.
(3) Organic Coating Repair: It is made by using various resins as binders and mixing them with a certain amount of filler. Its features include: it can be used in places where inorganic coatings cannot be applied, such as when toxic substances are not allowed in the medium. For instance, organic coatings remain stable in alkaline solutions. However, phenolic mortar, furan resin mortar, and epoxy mortar are widely used both domestically and internationally.
(4) Paint Repair: Currently, Bellzona 1311 is commonly used, while inorganic and organic paints are rarely used due to the higher requirements for formulation and application techniques, as well as their specific application areas. The general procedure for applying inorganic and organic paints is: rust removal, sandblasting and roughening the iron substrate, and removing damaged glass frit to ensure a strong bond between the paint and the lined surface. Layer-by-layer application, the coating area of the mortar should overlap the edge width of the glass frit by more than 10mm. Acid Treatment: After the mortar coating dries, it is treated with acid to form a silica gel film on the surface. Coating Surface: Once the paint application and treatment are complete, cover with a resin to prevent acid penetration.
