Featured Story – How to service a ‘Bugatti-valve’ part 2

Let me give an example from platform A and platform B. Both platforms are located on the same field under the same owner. Platform B is the wellhead platform, and platform A is the production and shipping platform. From each well there is one block valve into the production and test manifold between the wellhead on the B platform and the inlet to the A platform. All the valves are equal: 8″ class 1500 solid slab with a radial seal on the seat.

As long as there was only one valve into each line to the manifold, platform A had to shut down all import from the B-platform if there was work to be done on the well side of the manifolds on the B platform.

If the manifold valve were of the type solid slab parallel gate valve with radial seal on the seats, one could blow down the cavity pressure on the manifold valve, creating a double isolation on the valve.

But to do so, they needed an auxiliary valve installed into the cavity of all the valves. There was only one challenge: there was no valve but a lubrication fitting installed into the cavity. That fitting had to be replaced with a valve. However, looking at the photo in figure 1 which shows that the connection is an NPT. There’s a clamp connection close to the body connection and to top it all off, the threads were located close to the valve body. As one can see, there is no room to install a standard valve as a valve with an NPT-connection needs to rotate when installed.

I asked Tèchne Valves to come up with a special solution that could be installed above the clamp without crashing into the housing of the valve. The Italian company came up with a two-piece valve, as illustrated in figure 2.

On this valve, there is an adapter installed into the gate valve housing, and the auxiliary valve was installed on to the adapter. This 1/2″ special auxiliary valve with 3/4″ NPT-connection on the adapter was not cheap. As a 1/2″ valve, it could not compete with a standard valve. Most companies would hesitate to buy this valve type as the investment cost is higher than a standard valve.

The picture in figure 3 shows the auxiliary valve installed in one of the manifold valves. A short time after the valves were installed, a job came up, which normally would demand a delivery stop to the A-platform. But now, the maintenance crew only needed to close the manifold valve and empty the cavity pressure, establishing a double barrier in front of the manifold. This procedure enabled them to do the job on the well side with no stop required in the delivery to the A-platform. The savings on this one job paid for the investment in the special valve many times over. This is what I call a smart operation.

This auxiliary valve can serve several purposes: it can be used for setting double barriers, to test for leak rates into the cavity, or to enable cleaning the sealing surface on the interior seal surfaces.

When it comes to installing auxiliary equipment on major gate and ball valves, valve owners might be hesitant as it drives up the investment. We all know that the cost in replacing a major valve consists of four parts: First, the downtime cost which represents around 60 to 65 per cent; second, the labour cost can be up to 10 per cent; third, the price of the lost media will be in between 10 to 20 percent; fourth, the price of the new valve which represents 3 to 10 per cent of the total cost.

As indicated in figure 4, the cost price of a new valve represents only a fraction of the total cost. If by increasing the quality of the valve (which again typically would increase the price) one could double the lifetime and reduce the need for shutdowns. To me, this looks like a sound investment.

I have been in several discussions where people have claimed that there is no need for auxiliary equipment as long as the media is clean sales gas and the valves are manufactured for 50-year service. My experience over the last 40 years tells me that there is a lot to be gained by installing the proper auxiliary equipment and of cause implementing proper maintenance procedures.

To those who think that valves in clean sales gas don’t need any maintenance, I am sorry to tell you that is not the case. I have been involved with several cases of leaky valves in the UK (receiving sales gas from Norway) where replacement was discussed.

One example was a 24″ class 600 valve with a leak rate before maintenance 1.766 kg/min. We did maintenance on the valve and the leak rate the next day was down to 0.088 kg/min, well within the demands. The reason we were able to perform maintenance was that the 24″ valve was equipped with four lubrication fittings to the seat and an auxiliary valve into the cavity of the valve.

Maintenance does pay off.