Pipefitting, Joining and Fabrication Methods
This domain tests whether a joint you fabricate will hold gas for decades. It covers threading and assembly, welding and brazing, flaring, press fittings, CSST and polyethylene, plus support, protection and concealment rules.
Threaded steel
Cut square, ream to full bore, thread with sharp dies and cutting oil. Apply listed gas-compatible dope to the male threads (or gas-rated tape), leaving the first thread or two bare so excess cannot enter the pipe. Assemble hand-tight plus wrench turns, leaving roughly three threads visible. Never back a fitting off to align it - disassemble, clean, re-dope and use a fitting that lines up.
Welding and brazing
Welded joints require a qualified procedure and welder (ASME IX), proper joint preparation, purge and root control, and a hot-work permit. Never weld on a live gas line. Brazed copper joints need the correct alloy and flux, a nitrogen purge to prevent internal oxide, and complete flux removal because residue is corrosive.
Flare, press and specialty connections
Flared joints: square cut, deburr, correct 45° flare, no dope or tape on the seat, tighten to the specified torque. Press and mechanical fittings must be listed for fuel gas and made with the manufacturer's tool and jaws; mark the insertion depth and pressure-test before concealment. CSST uses the manufacturer's cutting and fitting method, with no kinks and proper support. Polyethylene is joined by qualified heat fusion with clean pipe, tracer wire and a listed transition riser.
Supports and protection
Hangers at code or engineered spacing, with extra support at valves and changes of direction; sleeves at masonry and concrete penetrations; corrosion protection at contact points; unions only where accessible; sediment trap at the appliance.
Worked example
A fitter's 1 in. nipple is tight and the union will not align, so he backs the nipple off half a turn. Why is this rejected? Back-off leaves a spiral gap with partial thread engagement, displaces the dope and creates a path that can leak under pressure or on thermal cycling. The correct fix is to remove the nipple, clean both threads, re-dope and install a shorter or longer nipple so the joint tightens at the required alignment.
Traps that cost marks
Dope pushed into the pipe bore where it can foul orifices and valves; unreamed burrs that reduce capacity and cause turbulence; tape or dope on a flare seat; welding without a procedure; and concealing a union or press fitting before the pressure test.