Derusting steps of steel pipe

With the continuous development of China's economy, the country to vigorously develop the energy industry, oil and gas pipeline is an important way of energy security, in the oil (gas) pipeline anticorrosion construction process, surface treatment of steel pipes is one of the key factors determining the service life of the pipeline corrosion, it is the premise of the anticorrosion layer and the steel pipe can be firmly combined with the. The research institutions of verification, except life depends on the type of coating, coating quality and construction of environmental factors such as anticorrosion layer, steel pipe surface treatment effect on coating life accounted for about 50%, therefore, should be strictly in accordance with the specification of anticorrosion layer on the surface of the steel tubes, constantly explore and summary, continuous improvement of surface treatment method of steel tube.

1, cleaning

The use of solvent, emulsion cleaning steel surface, in order to achieve the removal of oil, grease, dust, lubricants and other similar organic compounds, but it can't remove the rust, oxide skin, coating on the steel surface, so the production in anti-corrosion only as an auxiliary means.

2, cleaning tools

Mainly use wire brush tools such as grinding on the steel surface, can remove the loose or tilt of the scale, rust, welding slag etc.. Hand tools rust can reach Sa2 level, Powertool cleaning can reach Sa3 level, if the steel adhered on the surface of iron oxide solid, tool cleaning effect is not ideal, is not up to the requirements of the construction of anchor depth of corrosion

3, pickling

General use two methods to do chemical and electrolytic pickling treatment, pipeline corrosion only by chemical pickling, can remove oxide, rust, old coating, sometimes used as blasting after treatment. Chemical cleaning can make the surface reaches a certain degree of cleanness and roughness, but its anchor light, and easy to cause pollution to the environment.

4, spray (left) shot derusting

Spray (throw) shoot derusting by the high-power motor to drive the spray shot (impeller) blade to rotate in high speed, the steel grit, steel shot, wire section, minerals and other abrasive spraying on the surface of the steel pipe under the action of centrifugal force (left) injection treatment, not only can completely remove the dirt and rust, oxide, and abrasive role in the violent impact and the friction force of steel, can achieve the required uniform roughness.

(left) shoot derusting spray, can not only expand the physical adsorption on the surface of the pipe, but also can enhance the mechanical adhesion of coating and the pipe surface. Therefore, spray (parabolic) is an ideal way to shoot rust rust corrosion protection of pipeline. In general, shot peening (sand) is mainly used for surface treatment of pipe cleaning, shot blasting (sand) is mainly used for surface derusting pipe processing. (left) by spray derusting shot several problems should be paid attention to.

4.1 derusting grade

For the construction process, the steel commonly used epoxy vinyl, phenolic and other anti-corrosion coatings, the general requirements of steel tube surface reaches nearly white (Sa2.5). The practice proved that, the derusting grade removes almost all of the scale, rust and other dirt, anchor depth reached 40~100 mu m, fully meet the needs of the coating and adhesive steel, spray (CAST) operating costs shot derusting process at low and stable and reliable quality reaches nearly white (Sa2.5) technical conditions.

4.2 (left) shot abrasive jet

In order to achieve the ideal cleaning effect, should be chosen according to the steel abrasive surface hardness, corrosion degree, the original requirements of surface roughness, coating type, for single epoxy, two layer or three layer polyethylene coating, using mixed abrasive grit and steel more easily to the physical cleaning effect. A steel reinforced steel surface, and a surface steel grit etching effect. Mixed abrasive grit and steel in the steel (usually a hardness of 40 ~ 50 HRC, the steel hardness is 50 ~ 60 HRC can be used in all kinds of steel surface, even in the surface of steel C and D corrosion, rust removal effect is also very good.

4.3 abrasive particle size and proportion

In order to obtain better uniform cleanliness and roughness distribution, abrasive particle size and ratio design is very important. Roughness is too large to cause the coating in anchor lines thinning at the peak; at the same time as anchor lines too deep, in anti-corrosion coating process to form bubbles, seriously affecting the performance of anti-corrosion layer.

Roughness is too small will cause the decline of the coating adhesion and impact strength. For serious internal corrosion, not only large particles of abrasive high intensity shock, also must rely on small particles to polish the corrosion products to achieve the cleaning effect, at the same time reasonable proportioning design not only can slow the abrasive on pipeline and nozzle (blade) and abrasive wear, can greatly improve the efficiency. Usually, the shot size is 0.8 ~ 1.3 mm, steel grit size of 0.4 ~ 1 mm, with 0.5 ~ 1 mm as the main component. Sand pills than is generally 5 ~ 8.

It should be noted that in the actual operation, the ideal proportion of abrasive grit and steel in difficult to reach, the reason is hard and brittle steel is higher than the broken steel shot. Therefore, should be continuously sampling mixed abrasive in operation, according to the particle size distribution, to the incorporation of new abrasive derusting machine, and the incorporation of new abrasive grit, number of major.

4.4 derusting speed

Steel pipe rust on speed and abrasive in the abrasive type displacement, unit time that the abrasive is applied to kinetic energy total kinetic energy of steel tube and single abrasive particles. General should choose the loss rate lower abrasive, which helps to improve the cleaning speed and long life of the vane.

4.5 cleaning and preheating

In the spray shot (impeller) before treatment, remove the grease and the pipe surface fouling cleaning method, the tube body is preheated to 4 heating furnace