Slip-On and Weld Neck Flanges

While both components slide over piping, a slip-on flange is secured directly to the pipe, whereas a lap joint flange works in conjunction with a stub end fitting to allow rotation for bolt alignment. Both types are stocked across ASME pressure classes 150 through 2500, serving industrial piping systems, construction, and routine plant maintenance operations.

Installation of a slip-on flange involves positioning the flange over the pipe end so the pipe extends into the bore before securing it. The assembly is then aligned to connecting equipment according to project drawings. Contractors install these flanges within industrial piping systems, construction, and welding environments under ASME B16.5 and ASME B16.47 Series A or B specifications.

Slip-on flanges are governed by ASME B16 Series specifications, specifically ASME B16.5 for sizes up to 24 inches and ASME B16.47 Series A and B for larger diameters up to 72 inches. These standards define dimensions, pressure ratings from Class 150 to 2500, and material requirements across carbon steel, stainless steel, and alloy steel variants.

Yes, slip-on flanges are welded to the connected pipe during assembly. In construction, welding, and industrial piping systems, welders secure the flange to ensure structural integrity and pressure containment. They are manufactured from weldable materials including carbon steel, stainless steel, alloy steel, duplex, and nickel alloys meeting ASME B16 and API technical standards for field installation.

A slip-on flange is frequently referred to as an SO flange or slip-on hubbed flange in piping specifications and material take-offs. It is classified alongside weld neck, blind, lap joint, socket weld, and threaded designs used across industrial piping networks, petrochemical facilities, hydrostatic testing configurations, and pipeline projects.

A weld neck flange features a tapered neck designed for a butt weld connection, whereas a slip-on flange slides over the pipe. Weld neck flanges are typically preferred for severe service and high-pressure duties up to API 15,000 PSI or ASME Class 2500, while slip-on designs offer straightforward assembly across routine maintenance and general industrial piping applications.