First, the
stainless steel pipe gap
Stainless steel pipe due to equipment, component structure on the gap or the presence of metal or non-metallic deposits on the surface, in the sediment and the surface of the stainless steel pipe to form a gap in the role of corrosive media, the gap will be preceded by point-like and ulcerous injury , This 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 stainless steel pipe surface accumulation. Selection of crevice corrosion of high chromium, molybdenum and high chromium, molybdenum, nitrogen stainless steel pipe, is to provide pitting corrosion and crevice corrosion selection of stainless steel tube of 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 corrosion
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 repetition of the passivation are the key factors that can affect the corrosion fatigue of the stainless steel tube under the action of the medium and the alternating stress.
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 is the preferred material.
