MSS SP-43

Covers — thin-wall stainless steel fittings:

• Sizes from NPS 1/2 to NPS 24.
• Schedules: 5S and 10S (lightweight stainless piping schedules).
• Elbows, tees, reducers, caps, and returns matching B16.9 laying dimensions.
• Also provides detailed specific dimensions for Lap Joint Stub Ends (Type A and Type B).

Does NOT cover (exclusions) — the following are governed elsewhere:

• Schedule 40S, 80S, and standard carbon steel fittings → ASME B16.9.

Unlike B16.9 which guarantees the fitting has a burst strength equal to the connecting pipe, SP-43 fittings are designed primarily for lower pressure, corrosion-centric systems:

• Wall Thickness — The standard provides specific dimensional requirements for the thin walls to ensure they can be TIG welded properly without burning through the material.
• Stub Ends — The standard meticulously defines the radius and face profile of Type A and Type B stub ends to ensure they mate correctly with lap joint flanges without gasket failure.

In industries like food processing, pharmaceuticals, water treatment, and light chemicals, fluid pressures are generally low (often under 150 psi), but corrosion resistance, chemical purity, and cleanliness are paramount.

Using heavy Schedule 40S B16.9 fittings in these systems would be an immense waste of expensive stainless steel and nickel alloys. MSS SP-43 allows piping engineers to confidently specify thin-wall Schedule 10S or 5S fittings. This standardizes the layout dimensions (matching B16.9) while significantly reducing material costs and system weight.