The most straightforward way would be to mount them between flanges, after a section of pipe has been valved off and flushed.
This is correct. Blanking spades, also known as slip plates, slip blinds or spectacle blinds, are usually slipped in between two flanges after a process line has been double blocked and bled. They are usually secured in place by the flange bolts and sealed by a gasket or O-ring, similar to how wafer pattern valves are installed.
Sometimes dedicated 'blind flanges' are provided in the pipeline for this purpose, but often the inlet or outlet flanges on valves or equipment are used.
Blanking plates are used to provide an additional layer of protection during maintenance work, guarding against leaking valves or negligent opening of an isolation valve. Other important considerations when using them are:
- That they are installed in a sensible place, usually as close to the isolated equipment as feasible.
- That they are rated to withstand the upstream pressure.
- That they are removed before the pipeline is put back into service.