1、 Stainless steel pipe clearance.
Due to equipment reasons, there are gaps in the structure of stainless steel pipes, there are metal non-metallic deposits on the surface. A gap is formed between the deposit the surface of the stainless steel tube. Under the action of corrosive medium, pitting ulcerative damages will occur preferentially in the crevice. This is crevice corrosion. In the aqueous medium containing Cl -, due to the acidification of the medium solution in the crevice (the concentration of Cl - increases the pH value decreases), the passive film is partially destroyed due to lack of oxygen (oxygen concentration battery, the gap is low oxygen).
The basic method to eliminate the gap is to avoid the existence of gap in structural design. Appropriate measures should be taken to prevent the gap between tube tube sheet of heat exchange equipment, as well as between flange, gasket, bolt rivet. Clean regularly maintain flow rate ≥ 1.5m/s in seawater other environments to prevent dust (including marine life) accumulating on the surface of stainless steel pipe. Choose high chromium, molybdenum high chromium, molybdenum, stainless steel nitrogen stainless steel tubes with crevice corrosion resistance. The general idea of using stainless steel pipe to resist pitting corrosion crevice corrosion is provided. At the same time, it can be seen that in order to solve the crevice corrosion, it is more difficult to materials than pitting corrosion, the economic cost will be higher.
2、 It's a seamless tube phenomenon.
Under the joint action of stress medium alternation, the local corrosion of stainless steel seamless pipe is caused by the combination of mechanical (dynamic stress) electrochemical (corrosive medium). There are many reasons for corrosion fatigue. A consistent conclusion has been reached. According to the formation mechanism, the pitting stress concentration model, the preferential dissolution model of type changed metals, the rupture model of metal film the adsorption model of active substances were proposed. However, under the action of alternating stress, repeated action of passive film rupture, dissolution of sliding step re passivation are the key factors affecting corrosion fatigue. Stainless steel pipe processing process.
To prevent reduce the alternating stress of stainless steel seamless pipe equipment stainless steel seamless pipe factory components, including eliminating stress concentration surface defects on the structure of stainless steel seamless pipe, high fatigue strength, excellent corrosion resistance fine grain stainless steel seamless pipe duplex stainless steel seamless pipe are materials.
1. The size of casting should be too large: precision casting is suitable for casting small medium-sized castings several grams to more than ten kilograms. In recent years, although great progress has been made in the research production of large precision castings, Bijing still has its limitations. It's like sand casting.
2. Complex process: the precision casting process is various, the process is complex, the production cycle is long. The quality of bag casting has many factors. The production requirements of materials processes are relatively strict.
3. The cooling speed of casting is slow: the solidification cooling speed of investment casting is slow, the crystal structure is coarse. In addition to directionally solidified columnar crystals single crystal mussels, the properties of 304 stainless steel tubes for general alloy casting machine are comparable. The casting performance of the same material is low. In addition, the phosphor steel is easy to decarbonize.
It should be pointed out that any treatment method can only exert its advantages under specific conditions, so does precision casting. Here, it is important to meet the requirements of product quality performance. In addition, factors such as material energy consumption, production cost, price, service life reliability should be ignored. Stainless steel investment casting is a complex process in all blank forming methods, the casting cost is also high. However, if the products are correctly selected the parts are designed reasonably, the high casting cost is due to the reduction of processing, assembly saving of cutting metal materials. If compensation is made, investment casting has good economy, especially for the products of high melting point alloy with complex shape, high precision difficult to process shape, investment casting has advantages in technology economy, which is undoubtedly incomparable to other processes.