1. Scope

The full title of the current edition is "Integrally Reinforced Forged Branch Outlet Fittings: Socket Welding, Threaded, and Buttwelding Ends". MSS SP-97 includes essential dimensions, finish, tolerances, testing, marking, material, and minimum strength requirements for 90° and 45° integrally reinforced forged branch outlet fittings of buttwelding, socket welding and threaded types. It is maintained under MSS Technical Committee 105, Forged Steel Fittings.

"Integrally reinforced" is the operative phrase. The reinforcement is part of the forging — the saddle area is thicker by design, not by welding on a separate pad. Attached by a full penetration weld at an opening in the run pipe, the fitting makes a fully reinforced branch connection in accordance with the applicable piping code.

2. Product Types and Configurations

The names below are the commercial names used in the trade. SP-97 defines the fitting by its function and end type; the names are how the market asks for them.

Nipolet and sweepolet are trade names for contoured or extended designs that fall within the SP-97 intent but are not listed separately in the standard. Treat them as manufacturer's designs conforming to SP-97 requirements and confirm the reinforcement basis.

3. Pressure Class and Rating Basis

Socket welding and threaded outlets are supplied in the ASME B16.11 class designations — Class 3000 and Class 6000. ASME B16.5 does not publish Class 3000 or Class 6000 ratings; its classes are 150, 300, 400, 600, 900, 1500 and 2500. Citing B16.5 for an olet class is a specification error that will be picked up on review.

Buttweld outlets carry no class rating of their own. Their capacity is established by the branch reinforcement calculation in the governing piping code — ASME B31.3 for process, B31.4 and B31.8 for pipelines — against the run pipe and the design conditions.

4. Material Specifications

Match the olet material to the run pipe. The branch weld is between two different components and the weld procedure has to cover both.

5. Reinforcement — Why an Olet Instead of a Stub-In

A plain stub-in branch removes metal from the run pipe and replaces it with nothing, so the code requires a reinforcing pad or a thicker run pipe. An SP-97 fitting replaces that metal area within its own forging. The comparison below is the practical reason to specify one.

6. Tolerances, Testing, Finish and Marking

7. Related Standards

8. How to Order

9. FAQ — Frequently Asked Questions

What outlet angles does MSS SP-97 cover?

90° and 45°. Both are covered for buttwelding, socket welding and threaded ends. A 30° or 60° lateral is a special, not an SP-97 item.

Is "elbowlet" or "elbolet" correct?

The trade spelling is elbolet — an outlet fitted on the outside radius of a long radius elbow. "Elbowlet" is a common misspelling. Either will be understood, but elbolet is the form used by the manufacturers who originated the design.

Which standard sets Class 3000 and Class 6000 for an olet?

ASME B16.11. B16.5 flange classes are 150, 300, 400, 600, 900, 1500 and 2500 — there is no Class 3000 or Class 6000 in B16.5. Buttweld outlets carry no class at all; their adequacy comes from the code branch reinforcement calculation.

Does SP-97 fix a maximum branch size?

No NPS limit appears in the scope. Combinations are governed by the manufacturer's tooling and by the reinforcement calculation. Branch sizes approaching half the run size are usually better served by a reducing tee — check the code calculation before specifying a very large olet.

Can I use an SP-97 fitting in place of a stub-in with a pad?

Usually yes, and it is the common upgrade. The integral reinforcement removes the pad and its welds, which removes the pad edge fatigue detail and cuts the NDE scope. Confirm the replacement against the code reinforcement rules for the specific run and branch sizes.

Is a nipolet or sweepolet covered by SP-97?

They are trade names, not separate entries in the standard. A nipolet (extended threaded or beveled male outlet) and a sweepolet (contoured buttweld outlet) are manufactured as designs conforming to SP-97 requirements. Ask the manufacturer to confirm the reinforcement basis in writing.