NICKLE ALLOY STEEL FORGED FITTING ASME SB564 N10276 BOSS B16.11 MSS SP-97

NICKLE ALLOY STEEL FORGED FITTING ASME SB564 N10276 BOSS B16.11 MSS SP-97

I. Basic Definition

A boss fitting, also referred to as a forged branch outlet or half coupling, is a type of forged branch fitting governed by ASME B16.11. It is a compact heavy-wall fitting welded onto the outer wall of main pipes to tap small branch lines, instrument connections, drain and vent ports. It is simply called "boss head" in domestic engineering field.

II. Structure and Classification

1. Two Primary Connection Types

• Threaded Boss Equipped with internal NPT/BSP threads. After welding to the main pipe, it can be directly fitted with pressure gauges, transmitters, small valves and sampling tubes, widely adopted for instrument piping.
• Socket Weld Boss Designed with an internal socket bore for fillet welding of small bore pipes. It features superior pressure resistance and is applied to small-bore process branches. Less common types include butt weld bosses, extended bosses and flange face bosses.

2. Outline Characteristics

• Saddle-shaped curved base to fit the outer diameter of the main pipe for welding;
• Thickened raised boss projection on the top to reinforce stress at drilled openings and avoid rupture under high pressure;
• Fully forged construction with wall thickness much greater than standard short pipes, available in pressure classes 3000#, 6000# and 9000#.

III. Functions & Application Scenarios

• Tap small instrument branches on main pipelines (for pressure, level, temperature and sampling points);
• Provide small ports for pipeline venting, draining and air release;
• Serve as small-bore branch takeoffs (NPS 1/8" ~ NPS 4") as a cost-effective alternative to higher-priced olets;
• Standard fitting for high-temperature and high-pressure pipelines in nuclear power, chemical, oil & gas and power plant industries.

IV. Core Differences Between Boss and Olet

V. Materials and Standards

• Applicable Standards: ASME B16.11, MSS SP-97
• Common Materials: A105 carbon steel, A182 F304/F316 stainless steel, F22/F91 alloy steel, duplex steel 2205/2507,Nickle alloy
• Size Range: NPS 1/8" ~ 4"

VI. Supplementary Note: Distinct Boss Coupling Easily Confused

Boss coupling used in the hose industry is a quick-disconnect fitting for steam and air hoses, which is completely different from forged pipe boss heads. The term "boss" in piping engineering exclusively stands for forged saddle branch boss fittings.

A boss is a saddle-type forged half coupling branch outlet welded to the outer wall of main pipes, specially manufactured as reinforced connections for instruments, vents and small-bore branches.