Hot tapping machines are used to drill into pressurized pipelines to add or replace main or service lines without interrupting flow. The hot tapping process permits the installation of new pipes, fittings, and fixtures while a pipeline operates under constant pressure and/or continuous flow. Hot tapping machines are used with water lines, gas mains, oil pipelines, and in some petrochemical applications. They feature a retractable drill that separates a section of pipe in such a way that the cut or coupon is removed without interrupting service. Tapping sleeves and tapping valves are used as part of this process.
Hot tapping machines can be used with pipes and pipelines made of materials ranging from carbon steel to polyvinyl chloride (PVC). When selecting products, the line material and line contents are important considerations. Typical line materials include asbestos-cement, stainless steel, steel cylinder, carbon steel, ductile iron, cast iron, copper, and PVC. Choices for line contents include crude oil, gasoline, water, and steam. Hot tapping components include hot tapping valves, hot tapping sleeves, line measurement equipment, and pressure hoses.
To tap a live main, a branch saddle is positioned on the main pipe to create a temporary bypass line. After a small piece of pipe called the nipple is fused to one end of the tapping valve, the hot tapping tool is fused to the other. The tool’s overall length is measured, and the nipple trimmed accordingly. Next, a hot tap assembly is fused to the saddle fitting. When the tapping valve is open, the cutting tool is pushed through both the valve and the saddle to the main branch. By retaining the shavings and the plug, the cutter keeps the gas main free of debris. When the hot tapping tool is removed from the now-closed valve, the gas is purged from the assembly. The line is then butt-fused and opened for service.
In addition to adding new connections, hot tapping machines are used for product sampling, flow meter installation, thermo-well sensor installation, and pipeline draining. Hot tapping machines are also used with pipeline inspections, the installation of pressure control switches, product determination, and air relief points.