Selecting the Proper Pipe Fittings for Low Pressure Steam Systems

by | Sep 4, 2023 | News

Central steam systems play an essential role in heating, sterilization, and industrial processes by distributing low pressure steam throughout buildings and facilities. To safely and effectively transport this energy source, engineers rely on specialized pipe fittings rated for steam service. Let’s explore the key characteristics to consider when selecting fittings for low pressure steam lines operating below 15 psig.

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Material Requirements

Fittings carrying steam must withstand elevated temperatures without degrading chemically or structurally. Common alloy choices offering corrosion resistance include carbon steel, brass, bronze, and stainless steel, depending on design and conditions. High-zinc brass alloys work well for dry or saturated steam up to 250°F, while bronze valves handle intermittent wet steam up to 400°F.

Pressure Rating

Pipe fittings for low pressure steam intended for applications are typically rated at 0-15 psig and certified for use with steam at that pressure level or below. Higher pressure steam services require fittings rated for those specific pressures with proper safety factors built in. Verify fitting ratings match or exceed the system’s working pressure.

Steam-Tight Integrity

Given steam’s ability to condense within piping, all steam service fittings rely on pressure-containing sealing connections. Threaded joints use treated pipe threads with an anti-seize compound or PTFE thread seal tape to form reliable barriers. Socket weld or butt weld fittings join piping gas-tight through welding. Flanged fittings utilize full-face gaskets compressed between steel flanges.

Corrosion Resistance

Wet steam is corrosive, so internally smooth fittings resist corrosive attack and allow condensate to drain freely without pockets. Externally, coatings like electro-deposition or FBE (fusion bond epoxy) protect fittings during fabrication, transport, and installation. Stainless or plated carbon steel options further resist outdoor weathering.

Temperature Exposure

Continuous system operating temperatures generally range from 212°F to 250°F, though intermittent spikes can reach 300°F in trapped sections during startup or shutdown. Fittings must maintain integrity across this range without degrading or losing properties from heat stress.

Approvals and Certifications

Leading fitting manufacturers participate in third party material validation and stamping programs through entities like ASME and ASTM. Look for fittings bearing the symbol of approval organizations to ensure quality and safety compliance with design and manufacturing codes for steam service.

Common Fitting Types

Elbows, tees, reducers, couplings, and unions allow flexible routing and servicing. Ball valves or globe valves control flow. Drain fittings remove condensate. Bonnets seal threaded pipe openings. Flanges join boilers, tanks, and control valves. Dielectric fittings isolate dissimilar metals. Unions detach piping sections for maintenance access.

Proper steam fitting selection ensures low pressure systems transport energy safely and efficiently according to intended service conditions. Verifying material suitability, temperature exposure, approvals, and installation best practices delivers robust, long-lasting distribution piping.

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