In recent years, China's pipeline construction ushered in a new development of the peak. At the same time, the world market for steel pipe demand increases rapidly, so a large number of steel pipe exports. Behind the production and application of this prosperity, there has been some steel pipe quality issues.
Steel pipe surface quality
The surface quality problems is mainly in the thick surface oxide, surface cracking, surface re-skin, surface mechanical bumps. Hot-rolled carbon steel pipe in the finished or cold-rolled steel during the heat treatment after the formation of a layer of thick and strong adhesive force, high-temperature oxide. The presence of oxides is not only poor steel appearance quality will also affect the use of steel pipe, which is not allowed by the standard. Such oxides with the general sandblasting is difficult to remove, use pickling or mechanical polishing method to clear the construction site generally do not have the processing conditions. Operations, some Steel Plant has with such oxides steel pipe factory, a great deal of trouble to the scene Shi Ding. Therefore, before the steel pipe factory must Yan Geqing to get rid of such oxides.
Surface cracking occurred in the hot-rolled steel, which is common in carbon steel and alloy steel pipe, caused mainly due to the processing of residual stress caused by the huge surface tension, and after rapid cooling. Surface cracking does not belong to crack (not involving internal injuries), but it has some of the characteristics of the crack, in many conditions (such as heat, cold, stress corrosion cracking environment, etc.), it will be formed to some extent, notch sensitivity effects, which reduce the life of the steel pipe, and even steel pipe failure. Therefore, before the steel pipe factory, be sure to cracking cleared out. Surface re-skin is common in cold-rolled or cold drawn steel pipe, did not deal with due to the billet surface or abrasive. Re-skin the existence will seriously affect the appearance quality of the steel pipe, steel pipe was not cracking is severe, but in some situations will still have some impact. The improved approach is to strengthen production management, improve and control the billet surface quality and the abrasive quality. Mechanical bumps is one of the most common quality problems, mainly arising from the production, handling and transportation process. Steel pipe bumps Department will form a structural discontinuity in use is a source of stress concentration, but also notch sensitive. Compared with the crack, the clear outline of the mechanical bumps defects and does not involve the "internal injuries" of the metal, the standards allow a certain depth of the bumps, but in some of the more sensitive conditions, or bruise depth exceeds a certain value should be grinding to eliminate, making it a smooth transition.