Some of the most important valves are the ESD valves, which in most cases are parallel gate valves or trunnion mounted ball valves and many of them with a price tag of several hundreds of thousand euros or dollars.
Let’s take a look at the car industry. A Ferrari 488 Spider (a beauty of a machine) retails at a base price of USD 260,000. If you want a Bugatti Veyron, you have to add one more zero. But you could go for something in between, a Lamborghini Aventador S with a price tag of USD 400,000.
Having a car like one of the three mentioned requires maintenance. Only a basic service with an oil change in the Bugatti will set you back USD 20 to 25,000. But having that car, would you skip the change of oil due to the price? It is something that is called the cost of ownership.
Maintenance not possible
Let’s go back to the topic of valves. A 42” class 900 inlet ESD valve, parallel gate or trunnion ball valve, which will cost more than the Bugatti and is meant to protect personnel and equipment worth billions of US $. One tends to believe that maintenance of that valve is crucial. Believe it or not, in many cases the valve is not equipped with lubrication fittings or auxiliary valves, the upper bleed and the lover cavity drain is equipped with a blind flange as in fig 1, and there are no ways of performing maintenance on the valve. Purchasing a multi-million-dollar valve without the possibility of maintenance can be as getting a Bugatti without the possibility of changing oil. It sounds stupid, but it's the truth.
So, why do valves need auxiliary equipment? All valves need a good contact between the closing members, gate/ball towards the seats. To be able to create that contact, a moving part is required, and in many cases that will be a floating seal, which could be a gate or seats. To be able to seal off between the parts you also need clean sealing surfaces. Having deposits (like in fig 2) of heavy hydrocarbons build up between seats and gate/ball may prevent the necessary contact, and you end up with a leaky valve. When cleaning the gate with valve cleaner, the gate looks like in fig 3 and seals perfectly. Fig 2 and 3 is the same gate.
Some years ago, I was called out to a 42” class 900 inlet ESD valve. The valve was a solid slab metal/ metal parallel gate valve. The media was sales gas. The problem with the valve was as followed: the leak rate was too high to approve the valve at the yearly test. Looking at the previous leak tests, we could see that the leak rate slowly had increased over the years. As that valve was equipped with lubrication fittings to the seats and with an auxiliary valve into the cavity, it was possible to maintain the valve under full pressure. We closed the valve and injected valve cleaner into the seats. We left the valve to allow the valve cleaner to dissolve anything preventing the valve from sealing.
Still in service
After finishing the maintenance procedure, the valve was tested by reducing the cavity pressure through the auxiliary valve. The result: the leak rate was reduced by 80 per cent. This valve is still in service, tested every year, presently with a leak rate well below the limit. The media was sales gas which supposed to be 100 per cent clean.
In this case, we had auxiliary equipment installed on the valve and could perform maintenance on it, but without that equipment, we could not have done anything on the valve, and the result would have been to replace internal parts, and to do that a total shut down would have been the result, and you all know the cost of that!