The appearance treatment of the three links is one of the key elements to determine the pipeline anticorrosive life, and it is the premise of whether the anticorrosion layer and the three links can be separated firmly. Research institutes have proved that the service life of anti-corrosion layer depends on the coating type, coating quality, construction environment and other factors. The effect of the appearance of the three-way treatment on the service life of the anti-corrosion layer accounts for about 50%. Therefore, it is necessary to strictly follow the requirements of the three-way surface anti-corrosion coating specifications, from time to time to explore and summarize, and constantly improve the three-way surface treatment methods.
1. Cleaning
Cleaning the steel surface with solvents and emulsions to remove oil, grease, dust, smoothing agents and similar organic matter, but can not remove the rust, oxide scale, solder, etc. on the steel surface, can only be used as an auxiliary wrist to prevent corrosion.
2. Derusting things
The first choice is to use steel wire brushes and other things to stop the appearance of the steel, remove loose or warped scales, rust, welding slag, etc., manual rust removal reaches SA2 level, electric rust removal reaches SA3 level. If solid oxide scale is attached to the surface of the steel, the rust removal effect is not aspirational and the anchorage depth required for anti-corrosion construction cannot be achieved.
3. Pickling
Generally, chemical pickling and electrolytic pickling are used for pickling. The anti-corrosion tee only uses chemical pickling to remove scale, rust and old coating. Sometimes it can be used as reprocessing after sandblasting. Chemical cleaning can make the surface reach a certain degree of cleanliness and roughness, but its anchor pattern is shallow, which simply pollutes the environment.
4. Spray (throw) rust
Not only can rust, oxides and dust be completely removed, but the tee can also reach the required average roughness under strong impact and abrasive friction. After spraying (spraying) to remove rust, it can not only expand the physical adsorption of the pipe surface, but also enhance the mechanical adhesion between the anticorrosion layer and the pipe surface. Therefore, spraying (spraying) is an aspiring method of removing rust. Generally speaking, shot blasting (sand) is mainly used for surface treatment of pipes, and shot blasting (sand) is mainly used for pipe surface treatment. Several issues that should be noted when spraying (throwing) rust.
(1) Derusting level
Regarding the construction technology of three general-purpose epoxy, vinyl, phenolic and other anticorrosive coatings, it is generally requested that the appearance of the three-way reaches the near self-level (Sa2.5) theory that this rust removal level can remove all scales, rust, etc. The depth of the dirt and anchor pattern reaches 40-100μm, which fully satisfies the adhesion requirements of the anticorrosion layer and the tee, and the spraying (spraying) skills can reach the near-white level (Sa2.5) skill conditions, the running cost is low, and the quality is stable and reliable .
(2) Spray (spray) abrasive
In order to achieve the rust removal effect of aspiration, the abrasive should be selected according to the appearance hardness of the tee, the original corrosion degree, the required surface roughness, the type of coating, etc., single-layer epoxy, double-layer or three-layer polyethylene coating, steel sand and Steel shot mixed abrasives are more likely to achieve aspirational rust removal. Steel shots can strengthen the appearance of steel, while steel grit can corrode the appearance of steel. The mixed abrasive of steel grit and steel shot (general steel shot hardness is 40-50hrc, steel sand hardness is 50-60hrc) can be used for the appearance of various steels, even if it is used for the appearance of grade C and D corroded steel, the derusting effect is also very good .
(3) Abrasive particle size and share
In order to achieve better average cleanliness and roughness distribution, the planning of abrasive particle size and share is very important. If the roughness is too large, the anticorrosion layer will become thinner at the peak of the anchor lines; together, due to the deeper anchor lines, the anticorrosion layer simply forms bubbles during the anticorrosion process, which severely affects the performance of the anticorrosion layer.
If the roughness is too small, the adhesion and impact strength of the anticorrosion layer will decrease. Regarding severe internal pitting corrosion, it is not only the high-strength impact of large abrasive particles, but also the cleaning effect of small abrasive particles to grind away corrosive products. Together, a reasonable ratio planning can not only reduce the wear of the abrasives on the pipes and nozzles (blades), but also greatly improve the use rate of abrasives. The particle size of steel shot is generally 0.8-1.3mm, the particle size of steel grit is generally 0.4-1.0mm, and the primary component is 0.5-1.0mm. The shot-blasting ratio is 5-8.