WELDOLETS, THREADOLETS, SOCKOLETS
Branch fittings (also referred to as “O'lets” or branch connections) are used to branch pipes with different diameters (the main pipe is called “run pipe”, the branched pipe is called "branch pipe"). Branch connections are manufactured in a wide range of sizes, types, bores, classes and material grades (carbon steel, stainless steel, alloy steel, nickel alloys) and follow the manufacturing standards set in MSS SP 97.
The main branch connections are:
WELDOLET is the most popular branch connection: the branch is made by welding the item to the outlet of the run pipe. The ends of a weldolet are bevelled to facilitate the welding process, and for this reason weldolets belong to the family of butt weld fittings. Weldolets minimize the stress concentration on the branched connection and provide an integral reinforcement. Wel o let are available in multiple material grades and sizes.
SOCKOLET are similar to weldolets, with the difference that the branched pipe sits, and can be welded, on the socket that is available in the inside part of the olet. The bore of a sockolet matches the bore of the branched pipe. The Sockolet is considered a socket fitting, and is available in the 3000#, 6000# and 9000# classes.
THREDOLET are similar to weldolets, but the branched pipe is screwed inside the olet (which is generally NPT threaded) and no welding activity is therefore necessary. The bore of a sockolet matches the bore of the branched pipe. Thredolets are classified as threaded fittings, and are available in the 3000# and 6000# classes.
LATROLET are used for 45° lateral branched connections. They are available with butt weld connections to meet demanding reinforcement requirements or with socket weld / threaded connections in classes 3000# or 6000#.
ELBOLET is used in connection with 90 degrees LR / SR elbows for thermowell and instrumentation connections. Elbolets are available with butt weld connections to meet demanding reinforcement requirements or with socket weld / threaded connections in classes 3000# or 6000#.
NIPOLET are used for valve take off, drains and vents. Nipolets are manufactured in lenghts between 3 1/2 to 6 1/2 inches and for XS and XXS schedules. Nipolets are welded onto the runb pipe and are manufactured with socket weld or threaded outlets on the branched side.
SWEEPOLET has a contoured, integrally reinforced, butt weld branch connection suited for low stresses and long fatigue service. The weld on the run pipe side can be easily inspected with X-rays, UT (ultrasounds) and other non-destructive testing methods.
MSS SP 97
MSS, the Manufacturers Standardization Society, is one of the most important non-profit organizations that defines standards for various piping materials, including branch connections.
The standard MSS SP 97 covers the dimensions, the finishing, the tolerances, the testing methods and procedures, the marking, the material grades, and the minimum tensile strength requirements for 90 degree integrally reinforced forged branch outlet fittings of butt welded (like weldolets), socket welded (sockolets), and threaded (threadolets) types. Branch connections manufactured to the MSS SP 97 standard shall be designed and manufactured to ensure a fully reinforced joint in accordance with any applicable piping code requirement whenever joined to a run pipe by means of a full penetration weld. Branch fittings / o'lets may be manufactured to standard and non standard dimensions, sizes, shapes, tolerancess, or of other wrought material as agreed between the manufacturer and the buyer.