What is the cause of valve corrosion failure?

What is the cause of valve corrosion failure?

In order to adapt to the use of pneumatic tools for maintenance, the pipe diameter and cut-off valve of compressed air pipe in the public station can be appropriately increased, for example, DN25 is increased to DN50 equipment, and the pipe joint matching the public station can be shared with the exhaust vent of the equipment pipe; For large installations, a common material connection port (U.C) may be provided on the equipment. The connection port and the vent valve shall be located at the lower and upper part of the vertical equipment or at both ends of the length direction of the horizontal equipment respectively. When the common material pipeline may be contaminated by process fluid backflow, check valves shall be set downstream of the common material pipe cut-off valve.
Connecting: Basic setting of valve
Chemical process system professional in the design of high pressure waste heat boiler and steam system, can refer to the executive power
Relevant provisions of the Ministry of Industry and Power Construction Bureau:
Technical Regulations for Design of Steam Water Pipes in Thermal Power Plants (DLGJ 233-81)
Article 7~7 1: Pg≥40 pipe drainage and water should be set in series with two stop valves.
Article 7~8 1:Pg≥40 “for the vent device of the pipeline, two stop valves shall be set in series.
The unit of off pressure is kg /cm2(table).
When using, please pay attention to the provisions of the *** version.
For hydrocarbons, toxic and harmful chemicals and other materials and other process materials connection upstream and on the vent, vent pipe set double valves, can refer to Table 2.0.3
Table 2.0.3 temperature and pressure conditions for dual valves
Public material station (public engineering station) The public material station (common station for short) in the chemical plant can be set up according to the area covering a radius of about 15m, while the public station outside the plant area can be set up according to the design needs. The cut-off valve specification of each medium from DN15 to DN50 depends on the characteristics of the device.
The valves and joints of the public materials on the station can be intentionally inconsistent, and the order of the media in each public station should be consistent, so as to avoid the expansion of the accident of the wrong medium in the case of emergency.
The water pipes of outdoor public stations in cold areas can be done as follows:
(1) Multi-layer frame: according to the conventional pipe setting valve, cut off near the bottom ground and set a quick joint, when using water from the nearby water valve well. If fixed pipe and drain valve are used, the drain valve should be located in the valve well.
(2) In storage tank area or loading and unloading platform, the position of the valve well can be adjusted properly through consultation with water supply and drainage professionals, and the water supply valve can be located in the valve well.
(3) Heat preservation with steam pipe.
In order to adapt to the use of pneumatic tools for maintenance, the pipe diameter and cut-off valve of compressed air pipe in the public station can be appropriately increased, for example, DN25 is increased to DN50 equipment, and the pipe joint matching the public station can be shared with the exhaust vent of the equipment pipe; For large installations, a common material connection port (U.C) may be provided on the equipment. The connection port and the vent valve shall be located at the lower and upper part of the vertical equipment or at both ends of the length direction of the horizontal equipment respectively. When the common material pipeline may be contaminated by process fluid backflow, check valves shall be set downstream of the common material pipe cut-off valve.
tower
Keep the condensing steam pressure in the condenser on the top of the tower as much as possible as the same as the pressure on the top of the tower, the pressure drop of the pipe on the top of the tower to the minimum, except for the special needs of process control, no cut-off valve is set on the pipe from the top of the tower to the condenser. The connecting pipe between the reboiler (including the intermediate reboiler) and the tower body shall not be equipped with a cut-off valve, except for those required for process control or cleaning during the operation of the device.
When a valve is installed on the connecting pipe of the thermal siphon reboiler and the tower body, a gate valve with the same diameter as the connecting pipe shall be used. An 8-figure blind plate shall be installed between the valve and the reboiler, and the reboiler shall be equipped with their respective drain valves, as shown in Figure 2.0.5-1. Once through thermal siphon type reboiler should be in the reboiler material inlet and tower bottom discharge port between connecting pipe and set off valve,
What is the cause of valve corrosion failure?
Valve is commonly used control equipment, there are anticorrosive valve and non-anticorrosive valve, valve usually control the size of liquid or gas flow rate and switch, valve corrosion is one of the main reasons for valve failure, there are several forms of corrosion or the cause of corrosion, generally can be divided into six forms of corrosion. Corrosion is the natural and wasteful way of getting metals into their ores.
The chemistry of corrosion emphasizes the basic corrosion reaction of M0M + electrons, where M0 is a metal and M is a positively ionic metal, so long as the metal (M0) retains electrons, he remains a metal. Otherwise it will corrode. Physical forces Most of the time physical and chemical forces will work together to make the valve fail. There are many common varieties of corrosion, mainly overlapping. The corrosion resistance mechanism is due to the formation of a thick protective corrosion film on the metal surface. Then the reasons for the valve corrosion failure are listed below to make an introduction;
1, the pitting corrosion
Local corrosion or pitting occurs when the protective film is destroyed or the corrosion product layer is decomposed. The membrane ruptures to form an anode and the unruptured membrane or corrosion product acts as the cathode, effectively creating a closed circuit. Some stainless steels are easy to pitting in the presence of chloride ions. Corrosion occurs on metal surfaces or rough parts because these are not homogeneous.
2, friction corrosion
From the physical forces of wear and tear, the metal is dissolved through protective corrosion. The effect depends mainly on force and speed. Too much vibration or bending of metal can have similar results. Cavitation is a common form of corrosion pump, stress corrosion cracking, high tensile stress and corrosive atmosphere will cause metal corrosion. When the tensile stress on the metal surface exceeds the yield point of the metal under static load, the corrosion concentrates on the area of stress action, and the result shows a local corrosion. In alternating metal corrosion and the establishment of high stress concentration of parts, such corrosion can be avoided by early stress relief annealing, or the selection of appropriate alloy materials and design schemes. Corrosion fatigue We usually associate static stress with corrosion.
3, high temperature corrosion
To predict the effects of high temperature oxidation, we need to examine these data: metal composition, atmosphere composition, temperature and exposure time. But most light metals (those that are lighter than their oxides) form a non-protective oxide layer that gets thicker over time and falls off. Other forms of high temperature corrosion include vulcanization, carburization, and so on.
4, gap corrosion
This happens in gaps that block the diffusion of oxygen, creating areas of high and low oxygen and creating a difference in solution concentration. In particular, the joints or welded joint defects may appear narrow gap, the gap width (generally in 0.025~0.1mm) enough to make electrolyte solution into the gap, the metal and the metal outside the gap to form a short circuit galvanic cell, and strong local corrosion in the gap.
5, electrical corrosion
When two different metals are in contact and exposed to corrosive liquids and electrolytes, forming galvanic cells, the current causes the anodic piece to corrode and increase the current. Corrosion is usually localized near the point of contact. The reduction of corrosion can be achieved by plating dissimilar metals.
6. Intergranular corrosion
Intergranular corrosion occurs for a variety of reasons. The result is almost identical mechanical property destruction along metallic grain boundaries. Intergranular corrosion of austenitic stainless steel at 800 — 1500° F is subject to many corrosive agents (427 — 816°C) without proper heat treatment or contact sensitization. This condition can be eliminated by pre-annealing and quenching at 2000°F (1093°C) using low-carbon stainless steel (C-0.03 Max) or stabilized niobium or titanium.