As we talked before, the ASME B16.34 is a basic design for valve industry, including the valve sizes, valve pressure class, valve material, valve body wall thickness, pressure and temperature rating. API 6D is for valve specially in petroleum and natural gas industry.So there are 3 differences between these two standards:

1. Bore hole

The bore hole in API 6D is no reduced. The reason is in petroleum and natural gas industry; a lot of pipes are for crude oil with high viscosity and there will be deposited on the pipe and even block the pipe. So we use an equipment call pig to clear the deposit. In this way, the valve bore should be large enough for the pig to get through, that is the reason why we can not use reduced bore vale for the petroleum and natural gas.

2. The pressure relive

Since the petroleum and natural gas are sensitive fluid, the pressure increases when the temperature is going up. When the valve is close, some fluid will trap at the cavity, and the pressure will even exceed the rating class and that is very dangerous.

So liquid service shall be provided with an automatic cavity pressure relief.

Here is the working principle:

When the cavity pressure exceeds the line pressure , the seat is forced away from the gate surface, allowing the excess cavity pressure to be vented into the line.

Below the similar working pressure for ball valve:

  3.    Fire safe

When fire happens, the seal performance is important for API 6D vales, since they are used for flammable liquid or gas. In addition to soft seal, there is a metal seated behind the soft seat as the secondary seal. When fire happen, and soft seat broken, the spring pushes metal seat against the disc and form the seal for the valve.

The above is the 3 main differences between standard API6D and ASME B16.34. If any questions, you can contact TEKO INDUSTRY CO.,LIMITED.