A valve is a component that can be seen in a fluid flow system and also in a pressure system that would regulate the flow or pressure of the fluid. This regulation is done by controlling the flow rate, stopping or starting the flow, preventing the backflow, and also by controlling and relieving the pressure. The need for a control valve is very huge in many industrial applications. Most of the industrial processes are carried out with the control valve. So the operation of the control valve is very important and it should not be interrupted and because of this, we need to do the inspection of the control valve.
- How to do the control valve maintenance?
- How to do the control valve testing and what are the types of control valve testing?
- What is a special purpose valve and what are its types?
- What is a subsurface safety valve?
- What is an emergency stop valve?
- What is an anti-surge valve and what are their functions?
- What are the problems with the control valve?
- What is a pilot valve and how does pilot valve work
- What is a directional control valve and what are the types of DCV
What is the need for the inspection of control valve ?
The control valves are a very important part of a process certain control valves do the protection of the equipment during the over-pressure. So the proper operation of the control valve is required for equipment safety. So if we need to ensure the safety of the device then the control valve must be inspected. There are different types of control valves like globe valve, ball valve, etc, and each of them serves an important purpose in a process so if these valves are not working properly then the process will be interrupted or there could be equipment damage so we need to make sure that the control valve is operating properly. The inspection of the control valve parts must be done and if there are any abnormalities then they must be taken care of.
Inspection before the installation
The control valve should be inspected before its installation so that we can find out if there is any fault in the control valve and it can be rectified. Steps to do the valve inspection before its installation.
- The direction of the flow must be determined to ensure the proper installation, some valves are not bidirectional. So when swing check valves are installed then flow direction must be checked
- Visually check the valve and look for any foreign material in the valve because it can damage the valve
- The actuator position must be determined
In service inspection
The control valves are inspected in service to determine if there is any problem in the valve during its operation and also to check if the components are functioning properly under the routine operating conditions. During the inspection of the valve during the service, we would need to do certain adjustments such as adjusting the packing so that the valve can be kept in good operating conditions. We need to check the stuffing box and flanges so that we could know if there is a leak or not. So if there are defects in the valve then we should take action to recover them.
How to check a control valve while receiving it from the manufacturer?
Visual inspection
- Surface matching control
- Check the handwheel
- The seat body attachment and the seat control must be checked
- The finishing of the flanges must be checked
- Check the ports
- Check the body dimensions of the valve
- Check the end dimensions
- The finish on the flange face and ring joints must be checked
- Face to face dimension
- The outside diameter of the flange, bolt circle diameter, bolt hole diameter, flange thickness
- Body valve thickness
- Stem diameter and threaded ends must be checked
The field inspector must check the inspection documents and also for any mechanical damage that could happen during the shipping. We need to check if the valve is properly shipped or not.
The following factors must be checked to verify if the control valve is shipped properly
- All the valves should be completely drained of test fluid and it should be dried after the hydro-testing
- The end flanges and weld flanges of the valves must be fitted with covers, and the cover diameter must be the same as the outside diameter of the flange and it should be thick too.
- The raised face portion of the flange and the ring joint groove must be covered with heavy grease. A heavy-duty moisture-proof disc must be fitted between the greased flange face and the cover. The diameter of the disc should be equal to the inside diameter of the bolt holes
- The ends of threaded and socket weld end valves must be protected with tight-fitting plastic caps
Surface inspection
Linear and other typical surface imperfection must be checked for depth. If the depth is more than the acceptable limit which is specified for the wall thickness then these imperfections could be injurious. So the parts must be checked to determine if it is free from injurious imperfections. The mechanical marks on the abrasion and the pits must be acceptable and if it exceeds the acceptable limit then it must be removed by machining or grinding to sound metal. The marking should be on the body or in the identification plates and the acceptable marking methods are cast, forged, stamped, electro-etched, Vibro-etched, or laser-etched. The unidirectional valves must be marked with flow or pressure indication. The identification plate must be marked with the trim identification marking. The ring joining flanges must be marked with a ring groove number on the edge of the piping flange. There should be an indication for the ball, plug, or disk position for the quarter-turn type valves.
What are the required documents that must be checked before buying a control valve?
- Datasheet of the valve and approved drawings
- Offer list and correlation on the nameplate or tag
- Approved ITP/QAP
- MTC’s and lab test check reports
- Applicable NDT and test procedures
- Type test and fire test compliance
- NDT personnel qualifications
- Calibration certificates for measuring instrument and gauges
How to do the inspection of casting and forging?
- Raw material inspection and heat chart review
- Material identification, sample drawing, and mechanical testing
- NDT: surface defects – Wet fluorescent MPI for forging and casting
- Hardness and surface roughness
How to do the inspection of Block, gate, globe, butterfly, check, and ball valves?
- The castings and forgings must be inspected
- Pressure testing of the valves must be done like the shell, back seat, low and high-pressure closure.
- Fugitive emission testing
- Cryogenic and low-temperature testing
- Visual and dimension inspection as per the datasheet drawings
How to do the inspection of the pressure relief valves?
- Inspection of forgings
- Pressure testing of PSV, body, and nozzle
- Functional test of PSV- set pressure test, set tightness test, back pressure test.
- Visual and dimensional inspection
How to do the on stream inspection of the control valve?
- Correct relief device must be installed
- Check if the pressure settings are proper
- Look for any leakage
- Gas, blinds, closed valves, or piping obstruction should not exist
- The seals that protect the spring must not be broken
- Check if the relief devices are leaking or not
- An ultrasonic test must be done
How to ensure safety during the inspection of control valves?
Before we remove a valve from the line that section of the line containing the valve must be blanked from all sources of harmful liquids, gases, or vapors. So this part of the line must be depressurized and purged of all oil, toxic, or flammable gases. The inspection tool must be checked before the inspection.
How to do the inspection of a defective valve?
- Check the plant inspection log and also check the equipment inspection so that the valve failure symptoms can be determined
- The temporary repaired materials should be removed like clamps, plugs, etc.
- Inspect the valve for mechanical damage or for corrosion
- Check the bolts and nuts for corrosion
- Check if the build-up area has a proper thickness and also check the quality of the valve body
- Check if the gate or disc is properly secured to the stem
- The guides on both the gate and body must be checked for corrosion
- We should check the gland follower, if the follower is adjusted all the way down then additional packing will be required
- Check if the valve can be operated easily if not then the packing may need to be replaced
How to inspect a rebuilt or repaired control valve?
- If the parts of the valve are replaced then verify if the correct parts are installed
- We must also check if the trim material of the valve is proper for the type of service
- We must do a hydro-test so that we can determine if the repaired valve is suitable for the operation
- Seat tight test must be performed on the valve that needs tight shut off if the trim has been repaired or replaced
- If the gasket and the packing has been renewed then a tightness test must be conducted
