3/8 inch Black Iron Union Female x Female

3/8" Black Iron Union – Threaded Malleable Iron Fitting for Gas and Mechanical Systems

The 3/8" black iron union is a threaded fitting used to join two male-threaded pipe ends in mechanical piping systems where future disassembly may be required. Constructed from malleable iron, it includes a central ground seat that ensures alignment and tight sealing when assembled. Suitable for low- to medium-pressure applications, this union is commonly specified in natural gas, air, and non-potable water systems.

Technical Specifications

• Nominal Size: 3/8 inch
• Material: Black malleable iron conforming to ASTM A197
• Connection Type: NPT (female x female), ANSI/ASME B1.20.1
• Seat Type: Ground joint with central nut for disassembly
• Pressure Rating: Typically rated up to 150 psi for steam, 300 psi for water, air, and gas (dependent on application and code)
• Temperature Range: -20°F to 450°F (varies with application)
• Surface Finish: Black iron (uncoated); not intended for potable water or corrosive environments

Installation Guidelines

Install by threading onto properly prepared male pipe threads using a compatible thread sealant or PTFE tape. Avoid over-tightening, which can distort the mating surfaces. Ensure the union seat is properly aligned and torqued to provide a pressure-tight seal. Do not use in buried or potable water systems unless specifically approved.

Common Applications

This fitting is commonly used in:

• Natural gas and LP gas distribution lines
• Low-pressure steam and hot water systems
• Air compressor and mechanical utility piping
• Boiler rooms and service access points requiring union connections

Material Consideration

Black malleable iron offers good mechanical strength and moderate corrosion resistance for indoor use. For outdoor or corrosive environments, consider galvanized or coated alternatives. Not suitable for potable water use due to lack of corrosion resistance and lead content limitations.