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How to prevent back oxidation of stainless steel pipe during welding?

During the welding of stainless steel pipe in petrochemical construction, the surface of weld bead and heat affected zone are easy to be oxidized and discolored. In order to ensure the corrosion resistance of stainless steel, pickling and passivation treatment is carried out on the weld after welding to form a dense oxide film on its surface, but the inner wall of stainless steel pipe is unable to be pickled and passivated, which seriously reduces the corrosion resistance of the inner wall of stainless steel pipe. However, general welding process and construction measures are difficult to ensure the welding quality […]

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Explosion accident analysis of UNS S32205 duplex stainless steel pressure pipe……

Based on the analysis of a deflagration accident of a UNS S32205 duplex stainless steel pressure pipeline, the nondestructive testing, composition analysis, hardness testing, ferrite content testing, metallographic examination and mechanical property test were carried out on the UNS S32205 elbow. The influence of ferrite content of duplex stainless steel plate on the steel performance was studied. It was pointed out that hot forming was not considered in the design of 50% ferrite and 50% austenite respectively Or the effect of welding hot working on the decrease of microstructure and properties caused by the increase of ferrite content. It is suitable […]

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Causes of flange gasket failure and precautions

Generally, there are four types of leakage phenomenon of flange gasket: interface leakage, penetration leakage, diffusion leakage and damage leakage. Combined with many years of engineering construction, maintenance and manufacturing experience, the author thinks that the main reasons for seal failure are as follows: uneven distribution of compression force, stress relaxation, unsuitable surface roughness of sealing surface and temperature change. Uneven distribution of pressing force The uneven distribution of the pressing force will cause the gap of the flange gasket, which will cause the leakage. The uneven compaction force is caused by many factors. 1. It is man-made factor, asymmetric […]

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Detection and judgment of bending crack in angle bar

The angle bar in the transmission line tower needs the processing technology of opening angle, closing angle, bending and so on. In the production process, due to improper processing, the angle bar has cracks, and it is detected by ultrasonic according to the standard provisions. When the straight probe is used for detection, the detection direction of the straight probe sound beam is single, which is easy to form missed detection; when the oblique probe is used for detection of the diagonal steel edge, the ultrasonic wave produces the phenomenon of end angle reflection, and it is difficult to judge […]

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Effect of external potential on stress corrosion behavior of 316L stainless st……

316L austenitic stainless steel is a kind of ultra-low carbon stainless steel with carbon content less than 0.03%. Its material properties are equivalent to 00Cr17Ni14Mo2 steel in China [1,2]. 316L stainless steel, as the main material of PWR primary pipe and core components [3], has excellent mechanical properties and corrosion resistance, and is widely used in nuclear power field. 316L stainless steel flange is prone to stress corrosion cracking under the condition of stress and corrosive medium at the same time. This kind of corrosion is mainly caused by the destruction of the passivation film on the surface of 316L […]

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Analysis on the perforation of eccentric reducer behind the outlet valve of 1 ……

In recent years, with the increase of sulfur-containing crude oil import and the deterioration of crude oil quality, the corrosion problem of atmospheric and vacuum distillation unit, as the first process of crude oil processing, has become increasingly serious. Corrosion not only shortens the service life of the equipment and causes huge waste of energy, but also leads to disastrous accidents [1,2]. Therefore, the safety and reliability of atmospheric and vacuum unit equipment is more prominent. The atmospheric and vacuum distillation unit mainly distills crude oil by physical methods to generate gasoline, diesel oil, residue and other components, which provide […]

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Design idea of heat exchanger

What is a heat exchanger? Heat exchanger is a kind of equipment that transfers part of heat from heat fluid to cold fluid, also known as heat exchanger. Heat exchanger plays an important role in chemical, petroleum, power, food and many other industrial production. It can be used as heater, cooler, condenser, evaporator and reboiler in chemical production. Classification of heat exchanger: Shell and tube heat exchanger can be divided into the following two types according to the structural characteristics. 1. Shell and tube heat exchanger with rigid structure: this kind of heat exchanger is also a fixed tube plate, […]

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A complete set of pressure test methods for gate valve, globe valve and other ……

Generally, industrial valves are not subject to strength test in use, but after repair, the valve body and bonnet or the valve body and bonnet damaged by corrosion shall be subject to strength test. For safety valve, its constant pressure, reseating pressure and other tests shall conform to the specifications and relevant regulations. Before valve installation, valve strength test and valve sealing test shall be conducted on the valve hydraulic test bench. Spot check 20% of low-pressure valves, 100% of unqualified ones; 100% of medium and high-pressure valves. The commonly used media for valve pressure test are water, oil, air, […]

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How to carry out quality control when installing process pipeline in chemical ……

If the chemical plant is compared to a person, the equipment must be the “heart part”; the process pipeline for transporting raw materials, water, gas, finished products, etc. is the “artery”, which plays an important role in the production process. Therefore, at the beginning of project construction, it is necessary to strictly control the quality of process pipeline installation. If the quality is not good, it will greatly affect the normal production in the future. As a chemical construction unit, controlling the quality of process pipeline installation is the key to the survival of the installation enterprise, and also the […]

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Installation and inspection of high strength bolts

I. Preface The high-strength bolts for steel structure produced by domestic high strength bolts manufacturers mainly include A325 and A490 of American ASTM specification, f10t and s10t of Japanese JIS specification. Domestic high strength bolts manufacturers will produce bolts of Japanese and American specifications at the same time, because of the design specifications used in China, mainly referring to American AISC specifications; while the manufacturing and construction of steel structure factories mostly follow Japanese standards. Therefore, most of the steel structures of buildings use the torque control high-strength bolts of Japanese specifications, but the bolts used in bridge engineering are […]

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