Line Blanks and Applications in Piping Systems

Michael Mann

Line blanks, also known as “line blinds,” covered under ASME B16.48 standards are used to isolate a portion of pipe, usually for maintenance purposes. There are different types of line blanks used to isolate piping by generally inserting a solid disc with seals to eliminate the ability of upstream process liquids and gases to migrate downstream. Even if the seals failed, it is not possible for process fluids to migrate downstream. The different types of line blanks are the following:

Figure-8 Blank: These types of blinds have a circular, solid disc with seals for isolating. There is also a tie-bar that connects the solid disc to another similar disc, but one that has an inner-diameter so you can have unrestricted flow. The Figure-8 is secured by a bolt on the flange and can rotate between “blinded” (isolated) or “full-bore” position. These blinds are also known as “spectacle blinds” or “figure-8 blank”.

Paddle Blank: These blinds are solid circular discs with seals. There is a handle on the outer diameter of the disc so an operator can insert it between the flanges and isolate the piping.

Paddle Spacers: These spacers are like paddle blanks but have an inner-diameter hole to allow unrestricted flow. Paddle spacers are used to create a pressure containing gap between the flanges such that a paddle blank can be inserted when it is removed.

Furthermore, the operation of blinding can be cumbersome, requiring personnel to break apart flanged piping such that the blanks can be inserted. The connection must then be remade to the proper torque specification so that the connection is made pressure containing.  

Onis provides an advanced type of spectacle blind that is mechanized and doesn’t require the breaking and re-making up of flanges to perform blinding.

This type of blind is ideal if there is a higher frequency of blinding where reducing the blinding operation time by 95% could provide efficiency gains or increased capacity to a unit.

The Onis blinds provide an integrated cam system that can be used to separate and remake piping with ease by an operator moving a lever or turning a handwheel. The cam system multiplies the input force from the operator and provides adequate preload to make-up the pressure containing seals.

You can see a video animation of how an Onis line blind works:

You can learn more about Onis blinds and types ranging from 150# to 2500# pressure classes here.

If you would like to find out more or discuss a specific application, CONTACT US.