MSS SP-75 Standard Practice for High-Strength Butt-Welding Fittings
1. Scope:
1.1 Purpose:
- MSS SP-75 is a standard practice that addresses factory-made, seamless, and electric welded carbon and low-alloy steel butt-welding fittings.
- These fittings are designed for use in high-pressure gas and oil transmission and distribution systems. This includes pipelines, compressor stations, metering and regulating stations, and mains.
1.2 Areas Covered:
- MSS SP-75 governs various aspects of these fittings, including dimensions, tolerances, ratings, testing, materials, chemical and tensile properties, heat treatment, notch toughness properties, manufacturing, inspection, certification, and marking.
- It specifically focuses on high-strength butt-welding fittings with a nominal pipe size (NPS) of 60 and smaller. For NPS 14 and smaller, dimensional requirements are referenced to ASME B16.9.
1.3 Types of Fittings:
- The term “welding fittings” includes various types of butt-welding fittings, such as elbows, elbow segments, reducing elbows, caps, tees, single or multiple-outlet extruded headers, reducers, and extensions.
- However, it’s important to note that hot induction bends are not covered by this standard, and girth weld requirements fall outside its scope and are governed by relevant ASME B31 codes and customer specifications.
1.4 Specialized Fittings:
- Manufacturers and purchasers have the flexibility to agree upon specialized dimensions, sizes, shapes, tolerances, or materials that deviate from the standard’s specifications.
- Such specialized fittings, when they conform to other stipulations of this standard, should be considered in partial compliance and must be appropriately marked. They can be identified as “Part” fittings.
1.5 PSL2 Specification:
- If fittings are specified as “PSL2,” they are subject to additional requirements outlined in SR-24.
- These supplementary requirements complement the specifications for PSL2 line pipes in the API 5L Specification.
In summary, MSS SP-75 provides comprehensive guidelines for the manufacturing, testing, and usage of high-strength butt-welding fittings specifically intended for high-pressure gas and oil transmission systems. It also allows for customization while ensuring compliance with safety and quality standards.