With the rapid development of the domestic energy industry, application of stainless steel tube is rapidly increasing, the corrosion in oil and gas pipeline construction process, surface treatment of stainless steel tube is one of the key factors determining the service life of the pipeline corrosion, but also an important prerequisite for the anticorrosion layer and stainless steel pipe can be firmly combined with the. By the certification authority, in addition to life depends on the kinds of coating, coating quality and construction of environmental factors such as anticorrosion layer, surface treatment of stainless steel pipe influences on life accounted for about half, so must be strictly in accordance with the specification requirements of tube surface coating on stainless steel surface treatment technology, the continuous optimization of stainless steel tube.
At present, the common stainless steel pipe surface treatment methods are cleaning, derusting, pickling and so on, the following will introduce these methods.
The use of solvent, emulsion cleaning stainless steel surface, can remove oil, grease, dust, lubricants and other similar organic compounds, but this method cannot remove welding rust, oxide skin, stainless steel surface, so the corrosion production is only an auxiliary means.
The general use of steel wire brush and other tools to polish the surface of stainless steel, which can remove loose or tilted oxide skin, rust, welding slag and so on. Hand tools rust can reach Sa2 level, Powertool cleaning can reach Sa3 level, if attached to the surface of stainless steel iron oxide solid tool, derusting effect is not ideal, can not meet the construction requirements of the anchor depth of corrosion.
There are usually two kinds of chemical and electrolytic method for pickling, stainless steel pipe anticorrosion only by chemical pickling, can remove the scale, rust, old coating, sometimes also used this method as sand blasting after treatment. Although the chemical cleaning can make the surface reach a certain degree of cleanliness and roughness, but the anchor is shallow, and easy to pollute the environment.
Spraying (throwing) derusting
Spray (throw) shoot derusting by the high-power motor to drive the spray shot (impeller) blade rotating speed, the steel grit, steel shot, iron wire, minerals and other abrasive spraying on the surface of the steel pipe under the action of centrifugal force (left) radiation treatment, not only can completely remove dirt and rust, oxide, and stainless steel tubes in heavy abrasive the impact and friction force, but also can achieve the required uniform roughness.
Spraying (throwing) and derusting can not only expand the physical adsorption of stainless steel pipe surface, but also enhance the mechanical adhesion between the anti-corrosion layer and the pipe surface. Therefore, spraying (throwing) is an ideal rust removal method for pipeline corrosion protection. Generally speaking, shot peening (sand) rust removal is mainly used for inner surface treatment of tubes, shot blasting (sand) rust removal is mainly used for outer surface treatment of tubes. Several problems should be paid attention to using jet (shot) derusting.
For stainless steel pipe commonly used epoxy, ethylene, phenolic and other anti-corrosion coating construction process, usually require stainless steel pipe surface to near white level (Sa2.5). Practice has proved that the derusting grade removes almost all of the scale, rust and other dirt, anchor depth reached 40~00 mu m, fully meet the adhesion of anticorrosion layer and stainless steel tube, and the spray (throw) operation cost shoot derusting process at low and stable and reliable quality reaches nearly white (Sa2.5 technical conditions).
Jet (throwing) abrasive
In order to achieve the ideal cleaning effect, should be chosen according to the steel abrasive surface hardness, corrosion degree, the original requirements of the surface roughness, the type of coating, 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.
Cleaning and preheating
In the spray (throw) shot before removing the pipe surface grease and fouling by cleaning method, the tube body is preheated to 40 60 C heating furnace, the steel tube surface to keep dry state. In the spray (throw) shoot, because the surface of the steel pipe does not contain grease and dirt, can enhance the cleaning effect, is conducive to the separation of steel shot and steel grit and rust and oxide skin of the steel surface is dry, make the steel surface derusting cleaner.
In the production process of stainless steel tube to focus on its surface treatment process, process parameters and strictly control the scale removal, in the actual construction, the peeling strength of stainless steel pipe anticorrosion layer value is far higher than the standard requirements, ensure the quality of the anticorrosive coating, based on the same equipment, greatly improve the technological level, reduce production cost.
Source: China Stainless Steel Pipes Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)