The how (and why) of maintenance part 5
As explained in the previous articles in this series it is important to understand what can happen and why things do happens. In the last 40 years I have been working with valves, I have learned that the normal way of solving a valve problem is to by a new valve to replace the troublemaker. This is OK when having a flanged valve, but a little bit difficult when having in-line welded valve, in that case you only change the internal pars of the valve. This change of valve or valve parts may not solve the root to your problem, as the problem may be the operation, media, or lack of maintenance. The root to your problem may be a minor detail that causes a major problem. Let me tell you about a normal problem involving six identical valves in the same system.
On an installation there was this six, 10” class 1500 valves that all started to be troublesome. They all were identical and without lubrication fittings and a blind plug in the bottom of the cavity. The six valves was all getting harder and harder to operate and one had to use cheater bar and extension to be able to operate the six valves. The gear on one of them was dismantled, controlled and was found working as it should; the problem was clearly the valve.
As the valves were top entry, the plan was to strip the six valves, replace the internals to solve the problem. This would be a major operation as the proses had to be stopped and the system depressurised. Before starting the work, they asked me to come out to the installation to give a second opinion and se if there was anything I could do to solve the problems without having to shut down the system.
The six valves, as illustrated in figure 21, top entry valves where there are six places there normally can be friction. The normal friction between seats and ball are not taken into consideration.
- Between lower trunnion and body
- Between upper stem on the ball and bonnet
- Between stem and bonnet
- Between stem and stem packings
- Between stem and press gland
- Between stem and gear-adapter
The total friction on those six points + seat ball friction is the normal torque the gear must overcome.
It is not unusual that the material quality of the valve part not in contact with the media could be of less quality than the parts in contact with the media. The six valves was all 316, but looking at the valve the gear-adapter looked like it was made of carbon steel, and as we know that part is not in contact with the media. When condensation or rainwater falls down between the stem and gear adapter there can be a lot of corrosion if any of the parts are made of carbon steel
Looking at the VDS I could se that the gear-adapter and the press-gland was made of carbon steel, so my advice in this situation was to keep on producing and take the gear and the gear-adapter of the valves and control for friction between the gear-adapter, press-gland and the stem. After taking of the gear and the gear-adapter we saw what you can see in figure 22 that clearly shows what it looked like below the gear-adapter; it was full of corrosion. The picture in figure 23 shows the corrosion in the bottom of the gear-adapter, as one also can se in figure 23 there was a leak indication hole in the bottom of the gear-adapter witch allowed water to leak inn between the adapter and the press-gland. Figure 24 shows
how it look like after taken most of the corrosion on the top of the gland-plate away, and figure 25 shows the corrosion on the inside of the gear-adapter towards the spindle.
You don’t have to be a rocket science to understand why the six valves were stuck and impossible to operate. After cleaning the valves there was no problem operating them with a handle and the whole gear-adapter was filled with grease from the bottom to the top to prevent the same situation later.
The six valves had been in service between seven and eight years and newer had any trouble before suddenly they all were stuck. This story is not unique, there are a lot of valves in the same situation all over the world, and the valve manufacturer still produces valves with carbon steal gear / actuator adapter and carbon steel press-gland, and it´s nothing wrong with that. What´s wrong is that there are NO lubrication fitting in the neck of the adapter, and there is NO recommendation from the manufacturer to fill that adapter with grease.
There have always been too much money in the oil industry and policy have been; run to failure, and the problem solving have been to replace the valves when they fails to work like they should. I don´t care about the nice words like, life cycle cost, because the only thing that matters are the investment cost and the cost running the plants. I know that maintenance cost, it´s the same with you car. Why do you deliver your car for service? I do think it´s on time that this industry starts thinking about valve maintenance witch will save you billions.
But as I have tried to explain in previous articles; the valves MUST be equipped to be able to maintain them.
In the last years I have been working on big 36” 30 years old valves that was planned for replacement doe to operational and leak problems. I have many times heard: It´s on time to replace them, they are old and have done their job! After maintenance that takes a day, the valves works like they was new, no operational problem and a leak rate well below leak rate of new metal sealed ball valves. I have many times stated that more then 60% of all replaced valves could have been saved by the correct maintenance IF they where equipped with lubrication fittings in the right places and auxiliary valves in the bottom of the cavity. Maintenance does cost, but replacement is normally far more expensive.
To be continued
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