Tips for Valves Best Practices: How to get the Most out of Valves
A successfully commissioned valve is crucial for trouble free performance. Unfortunately, the period between valve testing and commissioning is when the valve goes through lots of abuse and mishandling leading to non-performance. Here’s an overview of the steps that should be taken in order to safeguard ball valves and ensure performance.
One of the most widely used shut off valve in an oil & gas pipeline or installation is a ball valve. Owing to industry requirements and huge demands, the valves are produced by a large number of manufacturers, world over. API 6D / ISO 14313, which is the most relevant or applicable standard, sets out material & dimensional requirements, design features and testing norms for these pipeline ball valves. Valves are made to specific project orders, involving drawing and quality plan approvals as well as third party witness tests. Tests include a high pressure hydrostatic shell test and seat seal test and when specified also conducts low pressure pneumatic test, high pressure gas tests and specified functional tests.
The period between valve testing at the valve manufacturer’s facility and a successfully commissioned valve in the pipeline is crucial for proper and trouble free performance of the valve. There are lots of points to be taken care of after the pressure tests, by the valve manufacturer and the end–user, which influences the long term satisfactory performance of these valves. Needless to point out that a valve which is leaking or hard to operate or completely jammed creates havoc with all work plans and deadlines. Unless a valve is set right, the pipeline commissioning cannot move forward. But the paradox is that many a times even a good valve is made bad at the work site, due to lack of knowledge on correct handling procedures.
Critical points of awareness
Each of the following pointers needs to be taken into account at the valve factory after pressure testing to ensure proper functioning of a valve:
- Valve internal should be thoroughly cleaned and dried after a successful factory test, as accumulated cavity water can corrode valve internals
- It is important that the cavity is subjected to a dewatering oil treatment, which would displace all the sticking water particles from the crevices
- Valves with seat sealant injection facilities are filled with ‘First fill of the lubricant’, on both the seats. This not only protects the seat but also covers the crevice between the ball and seat rings from external ingress of foreign particles.
- Always keep the valve in full open position. Charge the lubricant into the valve till it starts oozing out of the gap between the ball and seat rings ensuring that the seat rings are completely covered in grease.
- Additionally, as a temporary solution, paper tapes may also be used to seal off the crevices between the ball and seat rings and also the one between the seat ring back face and the valve body
- Ensure that open stoppers are properly set. This is extremely important, in full bore ball valves, as these valves go into main lines which are pigged.
- Extreme care should be exercised while handling the valve during its painting. Most specifications call for grit blasting, before finish coats. This calls for extra handling care as very many valve and actuator parts need to be masked, so that grit does not damage those delicate parts. Also ensure that grit does not enter the valve port, by any chance.
- Actuator and accessories shall be protected from possible transportation damages. Special metallic protection hoods shall be created on the valve while the valve is put inside the packing case.
- Caution stickers stating the ‘Do’s’ and ‘Don’ts’ should be placed on the valve and the packing case
- The valve should be packed for shipment with air-tight end closures to prevent dusty air & rain water from entering the valve port
- The packing case should carry labels with specific handling instructions.
The following pointers should be taken care of at the end-user’s site for optimal use of the valves:
- Valves must be handled only by authorized and trained staff
- The valve manufacturers instruction and operating manual should be carefully studied to ensure proper handling and use of the valve
- Store the valves only under a covered area and not directly on the floor
- Valves should not be removed from the packing case unless it is ready for field testing or installation
- Don’t remove end protectors till the valve is ready for testing or installation
- Refer to the caution stickers, ,if any, on the valve and act accordingly
- Use proper slinging method, while valves are taken up for installation
- If valves are to be re-tested at the site, it should be done in the presence of a valve manufacturer’s representative or valve technician.
Preventative Maintenance for Valves
As testing has proved, even minor scratches, on the ball surface, can lead to a valve leakage during gas testing. These scratches will continue to erode into larger leak paths if a preventative maintenance program is not in place.
The seat sealant system should be topped up with light grade synthetic lubricant or sealant. As the seat sealant system is filled, the previously injected sealant will be extruded into the valve body adjacent to the ball and seat ring interface. A valve technician should be called to inspect the valve thoroughly to ensure that the sealant is protruding around the circumference of the seat ring. Excess sealant should be smeared around the circumference of the seat ring to fill in the gap between the ball and seat ring and leveled so as not to overflow into the valve bore.
Methods such as blast cleaning should be avoided as this method could be a bit harsh on the internal parts of the valve. Sand, dirt, pebbles, sand blasting material, hand tools, timbers, are some of the many contaminants normally discovered in valve bodies, pig receivers and scraper / filter devises after start-up. Minor valve seat leakage is often the result of scratches to the seating surfaces caused by these contaminants. It would be ideal to keep a spool piece, in place of valve, while the pipeline is flush cleaned. However, this may not be feasible or practical in many sites.
Hydrostatic Testing Specifications
Hydrostatic testing when done should be in line with the valve manufacturer’s specification. First, the pipeline is filled with water, from one end of the pipeline, with all valves in the fully open position. This will push all construction debris downstream to the end of the test section, where it can be drained off. Once the water runs clean, shut the drain off point.
Prior to pressure testing, keep the valve in a half open position, as only the valve joints will get pressure tested. It is advisable to drain the valve cavity of accumulated dirt or foreign particles. Then, shut the drain plugs.
After all valves are kept in half open position, slowly increase the pressure, in stages. Check for body joints, stem top, sealant injection points, drain / vent threads for any possible leaks. T hen increase the test pressure to full rated pressure, as per pipe line commissioning procedures. All leak points shall be repaired prior to the introduction of gas into the system. Upon completion of a successful hydrostatic test, the valve should be operated in the full open position. The seat sealant system in the valve should then be topped up. Also, the valve should never be kept in the half open position for a long time. This can result in the elastomers or soft inserts in the seat ring to become deformed, resulting in severe seat leakage. After this, the pipelines or valves must be completely drained and dried.
High Pressure Gas Testing Specifications
For natural gas pipelines, high pressure nitrogen gas testing would follow the hydro test. While pressure testing the line with nitrogen, the valve should be operated first in the half open position to pressurize the body cavity and then returned to the full open position. The body vent or drain valve should then be opened and closed to drain the water from the body cavity. When all water has been removed, the valve needs to be brought back to the fully open position and lubricated further.
With the pipeline under normal operating pressure, the valve technician can now inspect the valve for seat leakage. Then, verification of each valve being tightly sealed in both full open and full closed positions can be done. Leakage, if any, is visually monitored by opening the body vent fitting with the main valve in the fully open or in fully closed position only. In the event that minor leakage persists, the valve should be topped up with more lubricant or sealant and the valve stops need to be adjusted in an attempt to achieve a perfect seal.
When the sealing is achieved, the actuator stops and should be locked in to position. In the event that a seal cannot be maintained, the valve manufacturer’s representative should be consulted for recommendations. In the event that leakage is very minor, a heavier sealant may be injected upon mutual consent of the operator, contractor and valve manufacturer.