The Positive Seal Coupling System is a press-on mechanical metal-to-metal interference fit and features a Coupling with finely machined internal serrations. The tapered interference internal surface of the Coupling is machined smaller than the OD of the line pipe it is designed to join.
This controlled interference fit, in conjunction with the serrations on the internal surface of the Coupling, produces a connection that exceeds the minimum yield specifications of the pipe itself.
Before the pipe ends are connected, a lubricant/sealant, normally a specially formulated epoxy, is applied to the outside surface of the pipe ends and the internal surface of the Coupling. Using the patented Positive Seal Field Joining Unit, the pipe is then hydraulically pressed into the Coupling to a pre-marked insertion dept—one half of the Coupling length—producing a connection with a metal-to-metal seal. The epoxy serves as a lubricant—preventing metal galling during Coupling installation — and cures to form a secondary seal around the pipe ends and throughout the Coupling-to-pipe interfacial surface. A shaped Seal Ring Gasket is also used between the pipe ends primarily to serve as a bumper to prevent pipe-end abutment damage. As an added feature, the energized gasket does form a redundant seal in the pipe connection.
Since no overlapping of pipe ends takes place with the Positive Seal Coupling System each joint retains its original length. “Bell and spigot” joining methods can reduce pipe up to one foot per connection just in insertion depth alone, as well as reducing line pipe ID, with a resulting reduction in flow characteristics. Those techniques also “cold work” the pipe ends which produces longitudinal stress risers in the “bell” as a result of the swedging operation. The stress risers cause the loss of expensive pipe due to “split ends” and increase the chances of sulfide stress cracking and corrosion.
The Positive Seal Coupling System (PSC) was first developed in 1979. The current patented design is a cost effective alternative to welding when it comes to joint coupling. High in strength with extensive mechanical and metallurgical re-engineering, the current design offers various applications. Hence, the PSC system is one of the most effective mechanical pipe coupling types which saves considerable pipeline construction time.