Valve inspection - main points of valve testing in Manufacture setting
Posted by Mark Trainer on Apr 16th 2024
Industrial facilities rely on different types of valves (such as check valves, for example) to control fluid flow, which is necessary for the continuity of several manufacturing processes. The design and manufacture of industrial valves follow diverse codes and standards to prevent valve failure and ensure they are durable, efficient, and maintainable.
Key Points
- Standards for Valve Production: Industrial valves are designed and manufactured to meet codes and standards ensuring durability and efficiency.
- Stress and Strain on Valves: Valves experience stress from pressure and temperature variations in processes.
- Valve Inspection and Maintenance: Regular inspections are crucial to detect fatigue and prevent failures.
- Non-Destructive Testing for Valves: Techniques like ultrasonic and dye-penetrant testing are used for detecting surface defects.
- Comprehensive Valve Testing: Essential for ensuring valve integrity under operational pressures and conditions.
These valves undergo repetitive stress and strain due to pressure and temperature variations, necessitating occasional pressure relief assessments in manufacturing and industrial processes. Valves can also undergo corrosion due to the physical and chemical properties of service fluid or sometimes even testing fluid. External stress and fluid corrosiveness increase the valves' susceptibility to failure. Valve failures, especially check valve failures, cause unexpected process downtimes and increase safety risks.
Manufacturing facilities use various valve inspection standards to identify early signs of fatigue and failure – which may result in lower efficiency, leakages, and fugitive emissions. These inspections are critical during initial installations and throughout the lifetime of industrial valves. In most facilities, valve inspection is a part of routine maintenance activities and happens at predetermined intervals.
Regular valve inspections, integral to the maintenance process and following industry-approved standards – such as API 598 and ISO 5208 – enable maintenance supervisors to identify and replace valves with high leakage rates to enhance their efficiency and thus improve the overall effectiveness of the production processes. What are the most critical valve inspection points in a manufacturing facility?
1) Valve body
The valve body houses internal components and is the primary pressure boundary with maximum exposure to fluid pressure. As fluids change flow and velocity at the valve sections, the resultant pressure acts against the valve body.
Valve bodies are made from materials possessing unique physical properties to protect them from premature damage or rupture due to fluid pressure. However, in time, they are liable to valve failure. Valve bodies also resist corrosion from the chemical composition and viscosity of the service fluid. The shell, often subjected to a pressure test, undergoes repetitive expansion and contraction due to the variation of process temperatures. Although the contraction or expansion is minute, their long-term impacts are noticeable.
Inspecting valve bodies provides valuable insight into the resilience and potential durability of the valve. Fatigue due to fluid temperature and pressure is likely to cause cracks and crevices on the valve surface; these cracks may be visible to the naked eye. Other surface defects require the use of advanced detection tools. There could be noticeable corrosion on the surface of the valve due to a chemical attack from the service fluid or due to a gradual loss of protective coating.
Technicians can also leverage non-destructive testing techniques to check for tiny surface irregularities and cracks and verify wall thicknesses of the valve. The most popular defect detection method is ultrasonic testing; other inspection methods include radiographic testing and eddy current testing.
2) Flanges, Gaskets and Fasteners
Valve flanges, integral to testing valves, connect adjacent pipes. They have unique designs to suit particular fluid applications. The flanges are connected to pipes using detachable connections like threaded or screwed joints and permanent methods like welding. Fasteners used for connecting pipes and valves are adjusted to a specific torque. It ensures valves are well secured and prevents valve misalignment – which may impede flow or cause vibrations, affecting the smooth operations of specific pipe sections.
When conducting a pressure test during valve inspection in a manufacturing facility, it is vital to prioritize flanges, gaskets, and fasteners. Loose connections, worn-out gaskets, or defective flanges can lead to leakages and fugitive emissions. Flanges may develop cracks due to variations in fluid flow conditions. Some inspection methods for these components include:
- Visual inspection of flange ends, gaskets, and fasteners. Technicians can identify cracks, rusty, broken, or missing fasteners.
- Ultrasonic testing of welded flanges to evaluate thicknesses and identify tiny cracks
- Using torque wrenches to check the tension of screwed connections
It is vital to replace worn-out gaskets immediately. Damaged gaskets are unsuitable for high-pressure fluid applications as they increase safety risks. When changing damaged valves, technicians should inspect the surface finish, end-to-end flange dimensions, fastener hole diameters, and flange thickness.
3) Valve Discs, Seats and Seals
Internal valve components like disks, shafts and seats come into direct contact with fast-moving service fluids. Internal valve components are optimized for media compatibility and durability. However, despite adhering to stringent manufacturing standards, seats, seals and discs undergo wear, erosion and corrosion, such as wire drawing, which causes valves to lose sealing efficiency.
Internal valve damage may be difficult to notice - inspecting discs, seals, and seats is possible during a scheduled process or plant-wide shutdown. Automated processes utilize condition-monitoring devices to monitor valve performances. Changes in valve performance indicate underlying defects and the production teams can plan a temporary shutdown for maintenance technicians to conduct further inspection and rectify the problem.
Internal valve components require comprehensive inspections at least once a year. Severe service valves and gas ball valves should be inspected in shorter intervals to ensure the seats and seals are in perfect working condition. The valve trim contains detachable and replaceable mechanical components. Any components that exhibit signs of fatigue require immediate replacement. The best approach is to confirm the quality of disc connection points, return springs, and the thickness of the flow control mechanism (ball, disc, or gate).
When non-metallic seals age, they become brittle, while some might even begin rotting. The ease of replacing these seals depends on the design of the valves. It takes less time and effort to replace seals in 3-piece ball valves than in 2-piece configurations. 3-piece ball valves have two detachable end caps and a central section; removing the end caps provides easy access to seals. In many cases, during the maintenance of a 2-piece ball valve, technicians need to remove it from the line, while a 3-piece construction allows the end caps to remain installed in-line. This way, the valve body can be removed or rotated to allow access to the seals in the center body section.
4) Valve Stem and Actuation Mechanisms
The stem, which connects internal valve components to the actuator, also undergoes corrosion due to the chemical action of fluids. It also undergoes surface wear and tear (due to friction between the stem and the packing as it moves to open or close the fluid flow path). The stem also experiences torsional and compressive stresses caused by actuator movements. As such, valve stems may fail if not inspected regularly.
Actuators provide the force to open and close valves and require routine inspections. It is important to note that an actuator that is not properly mounted to a valve will wear out the valve stem exponentially faster than a properly mounted valve. Therefore, ensure your products are being assembled and tested by a reputable source prior to installation.
Inspection points for valve stems include:
- A build-up of rust or ground metal (or plastic) on the surface
- Loose connection points (including bolts and nuts)
- Level of play or tightness of the stem
The level of inspection for actuation mechanisms depends on the type of actuator used. When inspecting electric actuators, check if electrical terminals, connectors, cables, and casings are well insulated. Check the power ratings of the external power supply, cleanliness of motors and lubrication on moveable parts like bearings. When handling hydraulic and pneumatic actuators, inspect cylinders, fluid supply systems, and filters.
Comprehensive Valve Testing - Ensuring System Integrity
Regular valve testing is an important factor in manufacturing settings, focusing on different types like check valves, control valves, and plug valves. This is an essential maintenance activity that involves various tests, each of which is tailored to assess specific valve conditions and general performance.
Key Testing Procedures
Valve pressure testing determines whether valves are able to withstand their operational pressures. Valve seat tests ensure the interface between the valve disc and seat is tight enough to prevent valve leakages, or allow an acceptable leakage rate. The valve shell test - which is another key procedure - assesses the general strength and integrity of the valve under specified pressure conditions.
Specialized Valve Type Testing
Distinct valve types, such as ball and globe valves and check valves, require specific tailored testing protocols. Globe valves are tested for their ability to control fluid flows for their operation in fluid systems. Tests on check valves will ensure the prevention of backflow, thereby improving the safety of the piping system.
Advanced Valve Inspection Techniques and Safety Protocols
Advanced valve inspection techniques are important in maintaining the safety and functionality of industrial fluid systems - although these methods are more than basic evaluations, accounting for the intricacies of valve operation and structure.
Preventing Valve Failures
Rigorous inspection plays an incredibly important part in preventing valve failures. This includes detailed checks of valve seat surfaces and the condition of the valve shell. Regular checks help identify early signs of wear or damage, such as cracks or corrosion, particularly in critical components like valve discs and seats.
Conclusion
Valve inspection forms a part of routine maintenance activities in a manufacturing facility. Comprehensive asset management plans must be devised to ensure adequate and timely maintenance of process valves.
Timely valve inspection allows companies to identify and rectify underlying defects and also extends valve durability, while facilitating uninterrupted continuity of processes. It also guarantees optimum operational safety. Valve inspection combines manual and automated inspection techniques depending on the number of valves, accessibility of valve chambers, and the intensity of inspection tasks.
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Sources
https://www.inspection-for-industry.com/valve-inspection.html
https://ethanolproducer.com/articles/valve-inspection-gets-easier-20163
https://www.britannica.com/technology/valve-mechanics
Mark Trainer, a Navy Veteran Aviation Electronics Technician and an authority in the valve industry, brings over 40 years of experience in process valves and controls to his role as an Outside Sales Representative for ValveMan.com and FS Welsford Company. His profound knowledge of valve types and control loops, coupled with his ability to provide strategic solutions, has earned him a reputation for reliability and professionalism. Mark's unwavering commitment to customer service and his ability to navigate complex technical challenges consistently result in successful outcomes, driving growth and delivering outstanding results for both companies.
