What Is The Corrosion Of The Seamless Pipe Crevice?
What is the corrosion of the Seamless Pipe crevice?
First, Seamless Pipe gap
Seamless Pipe due to the existence of gaps in the structure of the equipment, the existence of metal or non-metallic deposits on the surface, in the sediment and Seamless Pipe surface to form a gap in the role of corrosive media, the gap will be given priority in the point and ulcers Like injury, which is crevice corrosion. In the presence of Cl- and other aqueous media, the localized destruction of the passivation film due to the acidification of the medium solution in the gap (Cl-concentration increase, decrease in the pH value) and oxygen deficiency (oxygen concentration cell, gap oxygen deficiency).
Elimination of the gap is the most fundamental from the structural design to avoid the existence of the gap to start, the heat transfer equipment tube and tube plate joints at the gap, the flange, washers, bolts, rivets clearance, to take appropriate measures to prevent. Regular cleaning and in the sea and other environments to maintain the flow rate ≥ 1.5m / S, to prevent dirt (including marine organisms) in the seamless tube surface accumulation. Selection of crevice corrosion of high chromium, molybdenum and high chromium, molybdenum, nitrogen Seamless Pipe, is to provide pitting corrosion and crevice corrosion selection of Seamless Pipe the general idea. At the same time, it can be seen that in order to solve the crevice corrosion, starting from the selection is more difficult than solving the pitting and the economic cost will be higher.
Second, the phenomenon of seamless tube
In the alternating dynamic stress and medium under the action of the stainless steel Seamless Pipe caused by local corrosion. In the mechanics (dynamic stress) and electrochemical (corrosive media) under the joint action caused by the destruction of corrosion fatigue, many reasons, has yet to reach a consistent conclusion. In the case of its mechanism, a pitting stress concentration model is proposed, a preferential model of the metamorphic metal, a metal film rupture model and an active substance adsorption model. However, under the action of alternating stress, the rupture of the passivation film, the dissolution of the sliding step and the re-passivation of the passivation film under the combined action of the medium and the alternating stress are the key factors that can affect the corrosion process of the Seamless Pipe The
To prevent and reduce the stainless steel Seamless Pipe equipment and components received by the alternating stress, including the elimination of structural stress concentration to eliminate stainless steel Seamless Pipe surface defects; selection of high fatigue strength, corrosion resistance and fine stainless steel seamless tube, double Seamless stainless steel seamless is the preferred material.
Fire Seamless Pipe first clean up the welding mouth of the oil, paint, water, rust, and then according to the wall thick groove, thick to open some large, thin to open a small (angle grinder), and then is the goods Of the gap, usually the electrode or wire diameter of 1 - 1.5 times, if you do not care to open a large groove can be appropriate to stay smaller. Point welding at least three points, generally four points better work.
When the fire Seamless Pipe should be half of the welding, the starting point is better than the bottom of a centimeter or so, so from the opposite good joints. If the steel pipe wall thickness, it should be layered, at least two layers, the first layer of the whole circle welding can be welded second layer.
Fire-resistant Seamless Pipe surface with hot-dip plating or galvanized layer of welded steel pipe. Galvanized steel pipe can increase the corrosion resistance, extend the service life. Seamless use of a wide range, in addition to water, gas, oil and other general low-pressure fluid pipeline, but also for the oil industry, especially offshore oil wells, oil, chemical coking equipment, oil heater, condensing cooling Pipe, coal waste detergent oil pipe, as well as the bridge piers, mine tunnel support pipe and so on. Hot-dip galvanized steel pipe is widely used in various types of modern manufacturing industry.