Comparing fig. 2 with fig. 1, it is easy to see that there will be a price difference between the two valves. By eliminating the lubrication fitting, there will be a lot less machining on the seats and the body, and the amount of steel needed for the seats will be reduced.
Another example in reducing valve cost are in two illustrations in fig. 3 and fig. 4. Fig. 3 depicts a lantern ring with four seals with a lubrication fitting connected to the centre of the lantern. If the day should arrive that the valve starts to leak externally out of the stem, it is no problem to inject a sealing component into the lantern. I have done this several times and thereby stopped the external leak, all done in full production. Looking at the illustration in fig. 4, this seal consists of five graphite rings and no lubrication fitting. The only good thing to say about that one is that it is a low-price construction. However, if there is a leak, there is nothing you can do to fix this. You have to shut down and change the stem seal.
Life cycle costs
Life cycle costs, as most of us know, are completely different than investment costs. The lowest price is not always the most economical price, as in some cases expensive valves can turn out to be the most economical solution, provided they have a long life cycle. If maintenance is possible, the life cycle can in some cases be significantly extended.
Let’s put our illustrations into an example. The valve is a class 1500 trunnion mounted valve installed on the production manifold with heavy crude and sand. This valve should have metal-sealed seats and tungsten carbide coating on both the ball and the seats. In short, it will be a relatively costly valve.
Since most people look at grease fittings (or lubrications fittings, as I prefer to call them) as sealant injectors to be used in valves with soft sealing seats, they are in many cases eliminated on valves with metal sealing seats with TC coating. By eliminating the lubrication fittings, the valve manufacturer will reduce machining costs, and they can also use simpler and more economical seats (see fig. 2). This could save between 10 to 20 per cent of the investment cost. Selecting the stem seal illustrated in fig. 4 you will save even more. But what about the life cycle cost, or the total cost of ownership? If you have problems with a valve equipped with seats as in fig. 2 and stem solution as in fig. 4, you can’t do anything as the valve is not equipped for maintenance.
In the cavity, there is also a drain hole and/or a vent hole in which there are normally blind plugs or blind flanges. With blinds in the hole, the holes are absolutely useless.
But if a correct auxiliary valve has been installed in the drain hole, one can literally save millions when it comes down to valve maintenance and the setting of barriers to perform the maintenance.
But as the auxiliary valve will be an additional cost, it will normally not be installed—after all, the main objective is to save on CAPEX. The price of the valve is reduced and, moreover, several potential leakage points are eliminated, making the valve somehow more economical, and the buyer is satisfied.
But the result in this cost reduction may be that after one year in production, the seats get stuck in the seat pocket and the valve leaks significantly. What does one do with a leaky valve? One replaces it, with all the costs involved.