SEALANT INJECTION FACILITY ON TRUNNION MOUNTED BALL VALVES - A CONTENTIOUS ISSUE

The issue of the sealant injection facility on trunnion mounted ball valves with soft seat inserts is highly contentious. Over the years I’ve heard every argument ranging from people who say you should not even have a sealant injection facility permitted for fear of operators randomly pumping grease into a valve as they would a Plug valve or an API6D Gate valve which could then contaminate the product or also possibly attract grease or other debris which could further damage the seats. Technically debris should 'wipe off' but in practice this isn't always the case with larger particulates. Many people believe the valves can be permanently greased rather than just having the sealant injection facility for emergency use and that this will prevent seat damage allowing particles to 'slide off' the seat surface.. The mainstream train of thought recommended by most manufactures is that they’re only for emergency however, with the added advantage they can also be used for pre-flushing during commissioning or flushing in the event of some sort of sticking or seat damage problem before sealant injection is inserted. Also see our post on single sealant nipples to body (100NB & under) and how they cannot be greased in the same way as seat sealant nipples, click here. The below is an extract from the Australian Pipeline Valve Installation, Operations & Maintenance manual for Trunnion Mounted Ball Valves. You can see the full procedure and instructions at our website by clicking on this link. The reason people’s comments will vary so differently is it depends on what size, class, service, pressure range, valve design, etc., you are talking about. Also practicality, serviceability, cost factor and criticality of a leak all come into play in making your decision. Either way, you will find the Australian Pipeline Valve range of IOM’s invaluable for all types of valves, irrespective of what brand of valve you have in the line as our IOM’s cover important points that need to be considered for all brands with a similar design in the commodity Oil & Gas valve arena.

MAINTENANCE PRIOR TO FLUSHING

a- If the period between installation and flushing of the of the pipeline is longer than six months a preventative maintenance operation is suggested.

• Lubricate the stem with fluid protective oil through the stem injector (if applicable). Do not grease lubricate seats as grease may attract debris and damage seats.
• Remove valve from line and remove any debris and reflush.

FLUSHING THE PIPELINE

Flushing washes away all welding slag, dirt, sand, solids and debris collected in the pipelines during construction prior to turning the valve and potentially damaging the seat. Flushing where deemed necessary is the most dangerous activity for the valve, and it happens before they are put into service. Ball valves are normally not lubricated, however, should it be required to flush potential debris (or lubricate sticky valves) a different practise to the lubrication of either a gate valve or plug valve should be employed. We recommend the following: -

1. Find a good grease for natural gas or your service. The grease must be insoluble. It must be resistant to breakdown or shearing of the gel structure under high pressure injection and under the pressure between seating surfaces. It must be stable over a wide range of temperatures, and not freeze. It must not react chemically with the fluid and become solid, or rubber like (i.e. polymerize). Depending on the service, the best greases are fully synthetic; if you have any doubt or concern, consult a valve maintenance expert. Field experience has shown that greases and sealants may cause severe problems with the seat and seal arrangement if used regularly during preventative maintenance. If a non-leaking ball valve is lubricated with an adhesive grease/sealant, the floating, spring loaded seats can become stuck within their seat pockets. When the ball floats due to a pressure differential across the valve, the seals cannot track the ball and leakage can occur. Grease manufacturers produce low viscosity synthetic ball valve lubricants such as Clare UK “601-Fluid”. Such light greases offer the following advantages to heavier emergency sealant greases and cheaper brands of light greases:

• Enhanced resistance to hydrocarbon fluids and gases.
• Will not dry out or form a gum like some other greases when used within it’s application temperature range.
• Will not disrupt the operation of the seat and seal arrangement.

Of course, be warned any type of grease, especially synthetic grease can become hard or sticky causing torque problems and seat spring jamming in which case a line flushing agent like Clare 601 Valve Cleaner may be required. Of course, for leaking seats a heavier sealant like Clare 601 lubricant must be used for temporary emergency sealing.

CAUTION: Beware of greases made of synthetic oil with a mineral thickener. The natural gas (or storage prior to use) washes away the oil, leaving the thickener behind. The thickener is like a powder that caulks or bakes hard on the seats, increasing the operating torque. Always wipe the seats clean as much as possible prior to installation.

Do not operate the valve during flushing or entrained particulates could damage soft seat or enter stem or seat pocket area.

2. Use an appropriate high pressure grease-injection pump, capable of overcoming the pipe pressure and the high pressure build-up caused by the grease itself, during it’s injection in the grease passages.

3. Inject a generous amount of grease in the seats before flushing. The object is to cover them all and to fill the groove between seat carrier and ball with grease. The dirt will get stuck to the grease during flushing, but it will not come inside. And before turning the valve for the first time, inject again a small amount of grease into the seats. A little is enough (1/4 of the normal quantity per seat, see 8.4.1). The dirty grease will be pushed into the pipe by the fresh grease, and the turning action of the ball will drag fresh grease towards the seats, not dirty grease.

4. Do not turn the valve during flushing.

MAINTENANCE POST FLUSHING

a- At the end of flushing operation it may be possible to leave the line full of test fluid and in this case no intervention is required. If the line must be drained proceed as follows:

• Make sure that the valve is in full open position.
• Open plugs and drain it completely. Observe safety plant procedures prior to opening any body plugs in case any remaining fluid or gas is pressurised or trapped in body cavities.
• After draining flush the cavity of valve through the vent plug. Consult an expert on use of special excavation procedures.
• Lubricate the stem with fluid protective oil or grease through the injector (if applicable). (Seat lubrication is only for emergency purposes not for ongoing maintenance).
• Completely tighten all drain and vent plugs. Consult your plant safety procedures and only perform work under supervision of expert valve maintenance personnel.

b- Operate the valve at least 2 times (complete closing and opening operation).

c- Repeat the operation every 6 months if the pipeline is not used.

d- Always get authorisation to partially operate an in-service valve.

CAUTION: Personal injury may result from sudden release of any process pressure. APV recommends the use of protective clothing, gloves and eyewear when performing any installation or maintenance. Isolate the valve from the system and relieve pressure prior to performing maintenance. Never unscrew sealant injection nipples from body, seats or stem as these outlets are exposed to full line pressure and only the in-built check valve in the sealant nipple itself isolates the pressure. Similarly, the body drain and vent valve plugs are exposed to full line pressure if opened. Disconnect any operating lines providing air pressure, control signals or electrical power to actuators.

CAUTION: Natural gas is not usually clean. Natural gas may carry condensates and dirt that gets trapped in the valves, and may damage the internal parts. Also, operation of the valves becomes more difficult. It is true that plant sites do install filters in their system, but experience has proven that no system is perfect. The internal parts of the valve can be partially protected using judicious amounts of grease to fill the cavities. However, other than when flushing (see 2.4.3) or if there is seat leakage, or if valve cannot be opened, no grease should be applied via seat sealant injectors to soft seats as it will attract debris and cause damage. A soft seated valve is always at risk if service is not clean.

COMMISSIONING

The first year of operation is crucial, because when the pipe is put into service, all debris is pushed downstream, and contaminates the valves along it’s travels. With time, the pipe gets cleaner and initial problems disappear. Strainers or filters should be installed upstream of all soft seated valves.

Remember that ball valves in natural gas service are like the human body; they need ‘exercise’. Keep moving them and lubricating them, and you will have fewer problems. Do not let them have a sedentary life.

The same recommendations regarding grease injection for flushing (see 2.4) apply for commissioning. By refilling the grease channels multiple times, the dirt is gradually pushed out of the seats. Provided that the grease is properly chosen (see 2.4), it will not damage the valve, and to a certain extent will shield the seats from contamination. Regular cycling is also important, for two reasons: to prevent the seats from getting stuck, and to distribute fresh lubricant over the seating surfaces of the ball and seats. Once the seat is greased, it is a good idea to pump fresh grease into the seat to expel any debris laden grease (see 2.4.3) before cycling the valve to avoid damage to soft seat inserts. Many operators prefer not to grease seats even during commissioning as the grease can attract debris which can damage the seats if the valve is then turned. Also grease channels can become blocked if grease hardens. However, if the service is dirty the seats will damage either way, hence many users find regular greasing delays the damage. Should you need to apply grease to seats, ensure you then inject fresh grease to dispel any grease which may have attracted contaminants and then partially stroke the valve multiple times to remove as much grease as possible from the seats. After commissioning, once you believe the service is clean you can inject a suitable grease line flushing agent and then partially stroke the valve again. You should consult a valve maintenance specialist as different service, media, pressures, temperatures, etc., can require totally different practises. APV recommends the following programme for start up: -

1. For the first year, inject a small amount of grease into the seats before turning the valve, every time.
2. Cycle the valves periodically as follows:

• For the first month, every week.
• For the second month, every two weeks.
• For the third month, every month, for at least 6 months.
• Then every three months.

Depending on the type of seat inserts and type of particulates encountered in the media, after commissioning it is best to only use the seat lubrication nipples for emergency use as it is possible that grease on the seats will actually attract debris which can then damage the seats during closing or opening. Nylon and Devlon are hard and resistant to scratching, PEEK is even harder. Teflon? (PTFE) is softer and scratches easier, yet it can have more resilience and ‘memory’ in terms of resistance to permanent indentations. However, all soft seated valves are only suitable for clean service. Also note, PEEK seated valves have a higher operating torque. Teflon has the lowest operating torque, however it has more ‘memory’ and if left closed for a long period of time the torque required to unseat it will increase. Teflon is not suitable for larger sizes and higher pressures. Regardless of soft seat materials, valves need to be regularly partially stroked to prevent sticking of seats and accumulation of entrapped debris.

CAUTION: Beware of greases made of synthetic oil with a mineral thickener. The natural gas (or storage prior to use) washes away the oil, leaving the thickener behind. The thickener is like a powder that caulks or bakes hard on the seats, increasing the operating torque. Always wipe the seats clean as much as possible prior to installation.

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