What is positive isolation?

illustration pipeline maintenance positive isolation

Positive isolation explained

Many applications in the piping industry are required to shut off part of the production process to carry out maintenance operations on one or several pieces of equipment. During a maintenance operation, it is crucial to isolate the downstream side of the lines from the upstream side. This phase is necessary to prevent any potential risks to human health and material damage.

Positive isolation is the action of fully isolating a unit or a part of the plant from the active process. It is usually achieved by physically disconnecting a portion of pipe from the next one. This approach is mainly used in critical applications that require high safety levels, like steam cracker units, gas transportation, manifolds, tank farms, oil production, and many other petrochemical processes.

How does it work?

To ensure complete positive isolation, the traditional way consists of unbolting and spreading the flanges to insert a metal plate in between. Depending on the country, this metal plate may be referred to as a spectacle blind, slip blind, blind flange, paddle blind, blanking flange, or figure-8.

Unlike a valve, which cannot guarantee a completely sealed physical barrier due to its inevitable leakage, this metal plate provides a completely sealed barrier. Only the insertion of a metal plate between the flanges can guarantee a physical disconnection and thus a positive isolation. This step is most commonly called a blinding or blanking operation. Nevertheless, for several industries, the insertion of a spectacle blind, especially in very large units, is neither practical nor cost-effective. It requires specialized and expensive tools and is a time-consuming operation; plus, in congested areas, it is much more difficult to perform. It would be interesting, then, to find a more efficient and less expensive solution.

A comparaison between positive isolation and non proven isolation

Another way of implementing positive isolation is the use of Quick Action Line Blind. To understand this technology, one needs to understand how it works and how it differs from the usual way. A quick action line blind is a mechanical system that provides positive isolation in minutes without any tools. Moreover, it can be handled by a single operator. This method is widely used in the oil & gas industries, and it has been adapted to many others.

Depending on your process, positive isolation could be mandatory; that’s why it is essential to determine what isolation levels you require.

If you want to learn more about positive isolation, we made a video that summarizes this article just below. 👇