4 inch Black Iron Cap

4" Black Malleable Iron Cap – Threaded End Closure for Gas and Fluid Piping Systems

The 4" Black Iron Cap is a threaded pipe fitting designed to terminate the end of a piping run in non-potable water, air, steam, or gas systems. Constructed from malleable iron, this cap provides a durable and pressure-rated closure solution, conforming to ANSI/ASME B16.3 dimensional standards for Class 150 fittings.

Designed for use with Schedule 40 or heavier black steel pipe, this fitting is internally threaded (female NPT) and is typically installed with a suitable thread sealant to ensure a leak-tight seal under pressure. It is suitable for both commercial and industrial installations, where high mechanical strength and corrosion resistance are critical.

Technical Specifications

• ✅ Nominal Size: 4" Female NPT (National Pipe Taper) thread
• ✅ Material: Black malleable iron conforming to ASTM A197
• ✅ Pressure Class: Rated for 150 PSI non-shock at ambient temperature (Class 150)
• ✅ Compliance: ANSI/ASME B16.3 and B1.20.1 (threading standard)
• ✅ End Use: Threaded end cap for sealing unused pipe outlets or future connection points

Installation Considerations

Threaded iron caps must be properly aligned and tightened using pipe wrenches. Apply thread sealant or PTFE tape to male pipe threads before installation to ensure leak resistance. Over-torquing should be avoided to prevent thread deformation. In fuel gas or high-pressure systems, ensure all connections are tested for integrity per local codes and inspection protocols.

Common Applications

This fitting is commonly used in natural gas distribution, compressed air systems, oil supply piping, fire sprinkler lines (non-potable branches), and hydronic loop ends. It also serves as a temporary or permanent closure for future branch extensions or testing ports in mechanical piping networks.

Material Performance

Malleable iron provides excellent tensile strength and impact resistance. The black finish is suited for indoor or enclosed systems not exposed to potable water or corrosive moisture. For outdoor or corrosive environments, galvanizing or protective coatings may be recommended.

The 4" Black Iron Cap is a standard component for mechanical contractors working on fuel gas, air, and fluid handling systems. Its threaded design ensures reliable closure of piping ends while maintaining system pressure and structural integrity in accordance with applicable code requirements.