VALVE INSPECTION AND INSTALLATION

Valves are the most common equipment in chemical enterprises. It seems easy to install industrial valves, but if they are not carried out according to the relevant technology, they will cause safety accidents.

 

Inspection of Valves

1. Appearance Inspection of Valves

Before installing the valve, check the stuffing box one by one, whether the packing is full, whether the gland bolt has sufficient adjustment margin, whether the cast iron valve body has cracks, blisters and other defects. And make surethe valve stem is free from corrosion, bending, and the thread is free from defects.

 

2. Valve Pressure Test

(1) Some of low-pressure valves should be inspected from each batch (same factory, same specification, same model, and at the same time) for pressure test. If there is any unqualified, some of low-pressure valves should be inspected again. If it still fail, the pressure (strength and tightness) tests should be performed one by one.

(2) Valves on media with high or medium pressure and toxic and Class B fire hazards shall be pressure tested one by one for strength and tightness.

(3) The pressure test of the valve should be carried out by using clean water. For example, the working medium is a light petroleum product (such as liquefied petroleum gas) or a valve of a petroleum distillation product with a temperature greater than 120 ° C, and kerosene should be the pressure test medium.

(4) When the nominal pressure of the valve is less than 32 MPa, the strength test pressure value shall be 1.5 times the nominal pressure. When the nominal pressure of the valve is greater than 32 MPa, the valve strength test pressure shall be 1.3 to 1.4 times the nominal pressure. The test time is no less than 5 minutes.

(5) The gate valve with a nominal pressure less than 1.0 MPa and a nominal diameter more than 3600 mm can be tested without strength and tightness test alone, and it can be completed at the same time during the pressure test of the process system. The tightness test of butt welded valves must be carried out separately, and the strength test should be carried out during the system test.

(6) The valves that pass the test shall drain the internal water in time, coat the sealing surface with rust-proof paint, close the valves, close the entrances and exits, wrap them in plastic cloth, number them. After the valve pressure test record is filled in, and the storage should be ready for storage.

(7) Valves that fail to pass the test shall be disassembled for inspection and reassembled for pressure test.

(8) When testing the strength and tightness, we should try our best to remove the gas in the body cavity before starting the pressure. The pressure of the check valve during pressure test should be induced from the inlet end and blocked at the outlet end. When test globe valves and gate valves, valve discs and valve plates should be open.

Installation of Valves

1. General Requirements for Valve Installation

(1) Valves with flanged threaded connections shall be closed.

(2) When welding the welding valve and the pipeline, argon arc welding should be used to ensure the smoothness and smoothness of the interior. When welding, the valve should be open to prevent local overheating deformation. When welding the high pressure water injection valve, the valve body should be opened, and the rubber gasket should be picked out to prevent the rubber ring from being burnt.

(3) Before installing the valve, the direction of installation should be determined according to the direction of medium flow.

(4) Valves installed in horizontal pipelines should be vertical upward, horizontal upward or downward inclined by 45 degrees, and the center line should be aligned as far as possible.

(5) When installing cast iron valves, it is necessary to prevent damage caused by strong connection or uneven force.

2. Requirements for Safety Valve Installation

Installation and commissioning of safety valves must be carried out in accordance with the following requirements:

(1) Vertical, not inclined.

(2) When the pipeline is put into trial operation, the safety valve should be adjusted in time. The pressure for adjustment should be carried out according to the design requirements. If there are no design requirements, the opening pressure is 1.05 to 1.15 times the working pressure. The return pressure should be greater than 0.9 times the working pressure. Each safety valve should be adjusted more than 3 times repeatedly before it can be considered to be qualified and re-sealed. And it need fill out the "Safety Valve Investigation Test Record".

(3) The diameter of the safety valve inlet pipeline should not be less than the nominal diameter of the safety valve inlet.

(4) The outlet of the vent pipe discharged into the atmospheric gas safety valve should be higher than 2.5 meters above the operating surface.

(5) When the discharge pipe of safety valve is long, it should be fixed to prevent vibration.

(6) If the toxic or flammable fluid is discharged, the safety valve drain pipe should be 2 meters higher than the highest building or equipment around, and there should be without fire within 15 meters.

 

Valve plays a very important role in controlling the state of the whole operation system. Therefore, the inspection and installation of valves is extremely important.