Selection and installation of pressure vessel safety valve

In addition to the external pressure source from the container and can get reliable control, safety relief devices shall be installed, the device is to prevent the pressure vessel in use process of Chinese super pressure specialized equipment, it must ensure that during the normal working pressure of the pressure vessel not tight, and when the pressure inside the container once more than a specified value for some reason, which can automatically discharge quickly released containers within the medium, make the pressure vessels remain within the allowable stress. Therefore, safety relief devices must meet the safety valve discharge capacity is greater than the vessel’s capacity and the prescribed under the pressure of the accurate operation performance, the most versatile safety relief device is a kind of the static pressure on import automatic pressure relief valve (safety valve), it relies on its own pressure discharge amount of fluid to prevent container or inside the system pressure exceeds a predetermined TVC; When the pressure inside the container returned to normal, the valve to close, and prevent the media continue to discharge. Pressure vessel or not installed in the system relief valve or valve body improper selection, safety factor is not to be ignored, in this paper, combined with practical work experience in pressure vessel are introduced in the most extensive safety relief device is the key points of safety valve selection and installation.

1, the selection of the relief valve

1.1 the selection of safety valve principle

There are many kinds of safety valve, and its action is directly related to the stand or fall of the reliability and performance of equipment and personal safety, and closely related to energy saving and environmental protection. The selection of the relief valve should be pay attention to the following questions:

(1) the relief valve must be chosen have manufacturing license unit production of products, quality certificate and the nameplate data is complete.

(2) rating of the relief valve discharge capacity must be greater than or equal to the container of safety valve capacity.

Is generally selected. (3) the relief valve spring load type directly, if the relief valve is controlled by a pilot valve, you must request when the pilot valve and other auxiliary equipment failure, the main valve can still in not more than open automatically when the discharge pressure, side by side the full rated discharge capacity.

(4) for toxic, flammable, explosive or for refrigerant and other atmospheric pollution medium, and enclosed the relief valve must be used, is required if a hoisting mechanism is enclosed with a wrench should be used in the relief valve.

(5) for the opening of the steam pressure is greater than 3 mpa with relief valve or the gas medium temperature over 350 ℃ with safety valve, safety valve should be used with the radiator, have prevent discharge medium erosion spring directly.

(6.) when the relief valve may inherit the back pressure or under the condition of strong corrosive medium, should be chosen with bellows valve.

(7) on the relief valve regularly when you start the inspection requirements, shall be equipped with reliable hoisting mechanism; For toxic, flammable, explosive medium, unless users have special requirements, otherwise do not need to set the hoisting mechanism.

(8) in place of safety valve in large volumes should choose the safety valve, on the other hand, the safety valve in smaller volumes or requiring steady stress, appropriate chooses the safety valve.

(9) of the relief valve sealing surface type should be able to meet the requirements of the use of relief valve performance.

1.2. The selection of the relief valve

(1) the determination of nominal diameter

The determination of the relief valve nominal diameter shall be calculated according to the standard or actual use experience, first determine the minimum safety valve for the ensure the equipment safety measures; And then work out the minimum relief valve discharge area, according to the relief valve opening (rev. All or a tiny qi) to calculate the relief valve seat throat diameter, according to the slightly larger than the relatively close to calculate the valve seat throat diameter of standard series of the relief valve seat throat diameter, referring to the product sample to determine the safety valve nominal diameter.

(2) to determine the stress level

Safety valve of the nominal pressure and work pressure and work stress level has a different meaning of the spring, cannot confuse STH with STH else. Work pressure refers to the normal operation of the relief valve when the valve before under static pressure, it is the same as the protected equipment work pressure; And spring pressure level is refers to the working pressure range of spring is allowed to use, within the scope, the relief valve setting pressure can be adjusted by changing the amount of preloaded compression spring, of the same nominal pressure relief valve, based on the spring design requirements, can be divided into a number of different job stress level. Nominal pressure relief valve generally shall not be lower than the design pressure of the container, when its use at high temperature, the valve material allowable stress should be considered.

When choosing the relief valve, should according to the design pressure and the setting pressure to determine the nominal pressure of the valve and spring pressure level.

(3) determination of the valve material

Choose the material of the relief valve should take account of the working temperature and medium pressure; Dielectric performance and manufacturability of material, economy and other factors. Usually if no special requirements, when the valve nominal pressure is not greater than 1.6 MPa, choose grey cast iron; No greater than 2.5 MPa when choose carbon steel; The corrosive medium choose stainless steel; At higher temperature of chrome molybdenum steel.

2, the installation of safety valve

A professional safety valve before installation should be according to the working conditions for check regularly, at least once a year, the relief valve setting pressure generally shall be the highest working pressure container and shall not be higher than 1.05 ~ 1.10 times of design pressure (except for transportable pressure vessel).

Safety valve is installed correctly or not is the key to ensure the safety valve can ensure the safety protection, and in actual use, there are many units tend to ignore it. The installation of safety valve is usually to solve the following problems:

(1) relief valve shall be installed straight and level and should be installed in the pressure vessel more than gas phase space, or the gas phase space and connected to the pressure vessel, pipeline connected.

(2) pressure vessel and safety valve hole is the connection between the pipe and pipe fittings, the cross-sectional area shall not be less than import area of the relief valve.

(3) a joint installed on a couple of pressure vessels safety valve, the connection interface entrance area, should be at least equal to that of the imported a number of safety valve area combined.

(4) pressure vessel and safety valve should not be installed between the middle cut-off valve. To dress up for extremely flammable, toxic, highly, moderate harm or viscous medium pressure vessel, for convenience of relief valve replacement, cleaning, can be between pressure vessel and safety valve globe valve, cut-off valve structure and size of the size should not interfere with the normal discharge of the relief valve. Pressure vessel during normal operation, the valve must be kept open, and seal.

(5) the relief valve installed position, should facilitate inspection and maintenance.

(6) enclosed the relief valve should be equipped with a discharge pipe, gas emissions to outdoors or other safe place; Discharge pipe of the effective diameter should not be less than the relief valve outlet diameter at the same time, the applicant shall have reliable support, in order to avoid shock after the relief valve open or make the container produces additional stress too much. Increases and freedom also make the pipe emissions, emissions at high medium temperature can free expansion. The exhaust pipe and application of inflammable medium wire grounding.

(7) discharge tube if possible build-up condensate or rain, should be at its lowest position setting drainage tube, in order to discharge the condensate or rain at any time, make its not back pressure is produced.

Above all, the relief valve selection and installation of pressure vessel is reasonable or not, involves many aspects, and properly handle these problems, is a matter of equipment and personal safety, cannot treat STH lightly. It must be pointed out that the relief valve, should be timely find out the cause of the pressure vessel, suit measures to prevent pressure continued to rise.

References:

(1) "pressure vessel safety technology and supervision code" (99 edition)

(2) GB150-1998 "steel pressure vessel"