Isolation Methods

Positive isolation methods are those which remain effective even if there is equipment failure or operator error. These techniques apply not only to vessels, piping and tanks but also to pneumatic and hydraulic equipment.

The sketch shows some of the various isolation techniques that can be used to protect workers in the process industries. The process containing toxic or flammable chemicals under pressure is on the left; the open system, where the workers are present, is on the right. The order is from the least to the most secure.

After a piece of equipment or piping that operates under pressure has been opened and then reassembled (buttoned up) it must be pressure tested before being put back into service.

Process lines, piping and valves frequently become plugged. If line pluggage is a recurring problem it is best to try and identify ways in which the problem can be prevented from occurring. If that solution is not possible then valves, drains, tees and connections should be designed so that it is possible to remove the pluggage safely and with minimum time and expense.

The fluids flowing through many pipelines are two phase, i.e., a mixture of liquid and gas. Ideally the two phases separate out with the liquid at the bottom section of the pipe. The two phases flow together to a processing facility that separates the two phases. In practice, however, the two phases often travel at different rates which means that they can form slugs whereby the composition of the stream at different sections is almost all liquid or almost all vapor.

Pump seals are a frequent source of leaks in process and energy facilities. Moreover, the discharged liquid will normally be at high pressure, so it can travel a long distance and/or form a spray. Therefore, when laying out a facility it is important to make sure that pumps are located at a safe distance from other equipment and piping. (If the facility is already constructed and in operation it is still useful to consider spacing and layout guidelines.