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Leak-free plugs handle high pressures

Leak-free plugs handle high pressures

High pressure, high temperature manifold applications, such as those occurring in the petrochem and offshore oil industry, typically demand metal-to-metal devices which provide a leak-tight seal and meet API specifications. Lee Products has developed a range of AFO (axial force only) plugs which are both removable, reusable and are ideal for these high pressure / high temperature situations. 


AFO plugs feature a floating seal that self-aligns to allow for threaded holes that are not concentric with the through hole. As a result of the plug's two-piece construction, the seal does not rotate during installation, thus preventing galling of the seat. Also, since all the force is contained in the axial direction, the boss diameter can be smaller compared to other designs of plug.


Standard AFO plugs are manufactured from corrosion resistant 303 and 15-5 stainless steel and do not require O-rings or sealants. They are designed to withstand pressures up to 60,000 psi and temperatures to 600degF when fitted into hard materials as well as in softer materials, such as aluminium or plastic.


The plugs are available in sizes from .190in to .750in with UNF threads, however, depending on specific application requirements, special versions can be supplied. For example, to meet NACE standards required in the oil industry AFO plugs have recently been supplied in Monel in sizes up to 1,325in UNF threads. These special plugs were required to withstand 15,000 psi working pressure and 22,500 psi proof pressure.                                                                                                      


Current API specifications dictate that plugging devices must provide both primary and secondary seal. The AFO plug itself is considered to be the primary seal and because they are welded in position, the welding process satisfies the secondary seal requirement.


Whilst the oil industry has traditionally used NPT plugs, achieving a leak-tight seal with these types of plugs can prove difficult, particularly as PTFE tape is no longer permitted. If the NPT plugs do not seal first time, the thread often has to be recut due to the distortion caused by the tapered thread on the NPT plug. Typical offshore oil industry applications for AFO plugs include subsea wellhead trees, tubing hangers, completion tools, slick joints and down hole tools.

Lee Products

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