double block and bleed
double block and bleed
(OP)
what is the view on using a single block valve with a DPE (double piston effect) instead of using conventional DB&B valve arrangements. How does the double piston effect work. does it provide 3 genuine levels of safety similar to conventional DB&B valves





RE: double block and bleed
Benefits are that you can use one ball valve with DPE seats rather than the traditional arrangement of three valves. A DPE seated valve costs around 10% more than a traditional seated valve. There is the obvious associated weight and space saving.
The downside is that if the valve needs replacing for whatever reason, the line needs to be shut down. So Operations need to buy into this. With the traditional DBB, (assuming the downstream valve is still sealing), the valvbe to be replaced can be done so whilst the line is still pressurised. The single bodied DBB cannot be blinded.
The DPE DBB valve satisfies API 6D (pipeline)requirement, and API RP14E. Some Operators dont like it as they prefer to have 2 independantly bodied valves. Ask the client.
We have just replaced the 'traditional' DBB arrangment with DPE ball valves, after satisfying A Hazop study.