I think our requirements for corrosion prevention and insulation are quite simple. I wonder what others think?
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1. For ordinary applications (equipment pipes, supports, platforms, etc.), the requirement for metal corrosion protection is rust removal, which is generally achieved through mechanical grinding and manual grinding. The weld area is a key focus for rust removal. The rust removal grade is level 3. It is required to apply the primer (epoxy zinc-rich primer or epoxy iron oxide primer) once each, the epoxy etching primer once, and the chlorosulfonated topcoat twice. Quality requirements: Rust removal must be thorough and complete; no areas should remain untreated. The next coat of paint can only be applied after the previous coat has dried. Work must not be carried out in rainy weather. According to **(or industry) standards, various process pipelines are painted with a certain color of topcoat. 2. Anti-corrosion requirements for special applications 2.1 Buried pipes: The rust removal requirements are the same as those mentioned above. Painting: Three layers of fabric and five layers of coating; the fabric used is glass fiber fabric, and the coating is epoxy resin (or epoxy coal tar pitch). Construction method: Apply one coat of primer ； Apply the first coat thoroughly, then apply the second coat of oil ； Apply the second coat, then brush on the third layer of oil ； Coat it for the third time, then apply oil for the fourth time ； Apply the fifth coat of paint (topcoat). The next step of work can only be carried out after the previous coat of paint has dried. 2.2 Heat insulation and corrosion protection: The rust removal requirements are the same as above. Painting: It is required to apply a primer (epoxy zinc-rich primer or epoxy iron oxide primer) once each. 2.3 Pipes or facilities in water (concrete): Metal requirements for casting are the same as above ； The concrete needs to be leveled and dried. Painting: Four coats of paint, meaning four applications of epoxy resin or epoxy coal tar pitch. Requirements for insulation construction: insulation materials such as aluminum silicate needle-punched fabric and tubes, insulation mortar, as well as rubber and plastic sheets and tubes ； Outer protection: aluminum sheet, glass fiber cloth + paint, etc. 1. Thermal insulation: 1.1 Reactor vessel: Apply insulation paste (thickness of 1–2 cm); after it dries, apply protective glue + paint. 1.2 For the insulation of equipment and pipelines, aluminum silicate needle felt or tube shells are generally used. Insulation thickness: 50–120°C, thickness of 5 cm. (Layer 1): 120–200°C, thickness 10 cm. (Layer 2): 200–280°C, thickness 15 cm. (Three layers) 280-400°C, thickness 20 cm. (In the fourth layer,) due to high heat losses in outdoor areas, the insulation thickness can be increased appropriately. When carrying out outdoor insulation work, attention must be paid to waterproofing; in particular, the quality of the outer protective layer must be solid and reliable in order to reduce energy loss. General construction requirements: When constructing more than two layers, each layer must be tied securely; gaps should be filled, and the seams should be offset or overlapped. For those with a greater vertical height, thermal insulation nails or strips should be welded in order to prevent them from falling. The connection of the outer aluminum shielding requires rivets or self-tapping screws, with a spacing of 20-30 centimeters. 2. Cold insulation: Before applying insulation, carry out anti-corrosion treatment on the two bases first. Materials: Generally, BL-grade rubber-plastic panels or rubber-plastic pipe shells are used. Insulation thickness: for temperatures from 6 to 0°C, the thickness is 3 centimeters. (Layer 1): 0 to -10°C, thickness 6 cm. (Layer 2) – 10 to -20°C, thickness 9 cm. (Three layers) – 20 to -30°C, thickness 12 cm. (4 layers) General construction requirements: The glue must be applied thoroughly, ensuring a strong bond; when more than two layers are used, the gaps must be filled, with the joints aligned in an overlapping manner. The outer protection is aluminum sheet or glass fiber cloth + as required. I wonder if everyone will check the quality of rubber-plastic boards and aluminum silicate needle-punched felts? Discussion is welcome
There’s nothing wrong with this entire setup; as long as the inspections and sign-offs are carried out at each stage as required, there’s no issue with these types of concealed works. However, the key to the issue is that there are standards for ensuring the quality of the paint, as well as procedures for inspecting and verifying the rust removal on site; there are many tricks involved, but as long as everything is organized properly, there should be no problems. The key is how to manage it.
For manual rust removal, there are grades such as ST3, ST2.5, and ST2; for shot blasting, there are grades like SA2.5 and SA2. As for primers, inorganic zinc-rich primers and epoxy zinc-rich primers are available, with the choice depending on the specific circumstances.
Polishing to St-3 level for rust removal, followed by applying an epoxy zinc-rich primer – this combination isn’t very effective. Firstly, when a new steel structure is polished to St-3 level, its surface becomes too smooth, which hinders the adhesion of paint. Secondly, zinc-rich primers are meant to be used on steel surfaces that have been sandblasted to remove rust; it is only in direct contact with the steel that the advantages of such primers become apparent. If the oxide layer cannot be removed through polishing, it’s better to use an epoxy iron-red primer. When constructing buried pipes, the first four layers of oil and the three layers of fabric must be applied simultaneously; after they have dried, the topcoat can be applied. In my opinion, it is best to apply two layers of topcoat, as this yields better results. In my opinion, for cold-insulated pipes, it is more reasonable and cost-effective to apply two to three coats of epoxy coal tar pitch directly. For pipes submerged in water, applying four coats of coal tar pitch is not a problem; however, applying four coats of epoxy resin may lead to peeling and cracking over time. If epoxy resin is to be used, it is best to apply a layer of fabric first
“Polishing and rust removal, applying St-3 grade coating, followed by epoxy zinc-rich primer – this combination isn’t very good. This statement is very accurate; using zinc-rich paint for such a level of metal surface treatment is not suitable, as the roughness required isn’t achieved, adhesion is poor, and peeling occurs.
A careful analysis of such requirements shows that, if construction is carried out according to them, the quality of corrosion protection may not be sufficient. It is best to compare the requirements with relevant national and industry standards. Then, the requirements will be determined based on the actual usage of the equipment and other factors.