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Pipe Fitting and Threading

Cut, thread, and connect piping systems for water, gas, steam, and hydraulic applications

⬢ 層級 1領域
高
薪資影響
12 個月
學習時長
中等
難度
6
職業
一覽

Pipe fitting and threading is the craft of selecting, measuring, cutting, bending, threading, and connecting piping systems that transport fluids (water, steam, gas, oil, hydraulic fluid) in buildings and industrial equipment. Practitioners master thread types (NPT, NPTF, pipe, metric), cutting and threading by hand and machine, fitting selection (elbows, tees, reducers, valves), sealing methods (thread tape, sealant, flare), pressure testing, and installation codes. Work spans plumbing (domestic water supply and sewer), steam and hot water heating, refrigeration and HVAC, natural gas distribution, and industrial hydraulic and pneumatic systems. Career path: Apprentice Pipefitter (1-5 years, $35-50k) to Journeyman Pipefitter or Plumber (5+ years, $55-75k) to Master Plumber or Supervisor (10+ years, $75-110k+). Built on geometry, hand and power tools, and code knowledge.

什麼是 Pipe Fitting and Threading

Piping systems are the arteries of buildings and industrial equipment. Practitioners who can cut, thread, fit, and seal pipes with precision and speed are invaluable on plumbing, HVAC, and mechanical projects. Pipe fitting and threading is the craft of assembling piping systems that transport fluids from a source to a use. It includes selecting the right pipe and fitting materials (steel, copper, PVC, PEX, cast iron), measuring and cutting pipe to exact length, threading steel pipe with hand or machine dies, bending pipe around obstacles, selecting fittings (elbows, tees, unions, valves), sealing threads with tape or dope, tightening and testing for leaks. High-pressure systems (steam, nitrogen, refrigerant) demand precision; low-pressure systems (drain, vent) are more forgiving. A single bad thread or loose connection can cause water damage, gas leaks, or equipment failure.

🔧 工具與生態
Pipe Cutter (wheel and threader)Pipe Threading MachinePipe WrenchAdjustable WrenchTape and Dope SealingFlare ToolBending Spring or Pipe BenderPressure Gauge and Test PumpDeburring ToolThread Sealer Tape

💰 各地區薪資

地區初級中級高級
USA$35,000$60,000$85,000
UK£23,000£40,000£58,000
EU€26,000€45,000€65,000
CANADACA$42,000CA$70,000CA$100,000

❓ 常見問題

What are NPT threads and how do they differ from other thread types?
NPT (National Pipe Thread) is the US standard for pipe threads, with a tapered design so threads grip and seal as you tighten. The taper is 1 inch per 16 inches of length. NPTF (National Pipe Thread Fuel) is a variant with deeper roots for higher pressures. Metric pipe threads (M) and ISO taper threads (R, Rc) are standards outside North America. Never mix thread types: an NPT male on an NPTF female will leak under pressure. Always check the fitting specification. Sealing NPT requires thread tape or sealant compound; flared connections use a different mechanism (cone-to-cone contact).
How do I know what pipe size to use for a water supply or gas line?
Pipe sizing depends on the flow rate (gallons per minute for water, cubic feet per hour for gas) and allowable pressure drop. A supply line to a single fixture (toilet, sink) is typically ½ inch; a main to a house is typically ¾ or 1 inch. Gas lines are sized by BTU load; a furnace and water heater might need ¾ inch copper or 1 inch black iron. Building codes specify minimum and maximum sizes, and pressure loss tables help you choose. Undersizing creates slow flow or pressure loss; oversizing wastes material. Consult the plumbing or gas code for your jurisdiction or a sizing chart from a supplier.
What is the difference between hard and soft solder (or braze) for copper pipe?
Soft solder (lead-free tin-silver, melting point ~430°F) is used for water supply lines and low-pressure applications. Hard solder and brazing (copper-phosphorus or silver-based, melting point >1100°F) are for refrigeration, high-pressure steam, and where joint strength is critical. Soft solder is easier to learn (lower heat required) but weaker; hard solder is faster and stronger for experienced technicians. Always choose the joint strength appropriate for the application and code requirement.
How do I thread a pipe by hand and avoid cross-threading?
Use a pipe die (circular cutting tool) fitted in a die stock (wrench-like handle). Start with the die centered on the pipe end, lightly butted against it. Apply cutting oil and rotate the die stock clockwise with moderate pressure. After each turn, reverse slightly (about ¼ turn) to break the chip and prevent jamming. Stop when the die is thread-deep (listen for the sound change or feel the resistance rise). For a machine threader, feed the pipe slowly and let the machine do the work. Cross-threading (threads misaligned) causes leaks and a stripped fitting; it happens if you start at an angle, so square the pipe to the die carefully.
What is the pressure test procedure for a new piping system?
Pressure testing verifies that all joints hold under load and there are no leaks. For water, fill the system with water and use a hand pump or air pump to pressurize it to the code-required pressure (typically 1.5 times the working pressure, e.g., 75 psi for a 50 psi system). Leave it under pressure for 15 minutes and watch the gauge—if pressure drops, there is a leak. For gas, use nitrogen (never air or oxygen, which are explosive) at low pressure (10-20 psi) and listen for hisses or spray soapy water on suspected areas. Document the test (date, time, pressure held, pass/fail) and retain records for inspection.
What thread sealant should I use: tape or dope, and how much?
Thread sealant tape (PTFE, white or yellow for gas) or pipe dope (liquid sealant) both work; many plumbers use both (tape plus dope for extra security). For tape: wrap 3-5 layers clockwise (the direction of tightening) around the male threads, overlapping slightly. Yellow tape is rated for gas and oils; white for water. For dope: apply a thin coat to the male threads before threading into the fitting. Don't overapply dope; excess can wash into the system and clog filters or valve seats. Gas fittings require either yellow tape and dope, or a product rated for gas; never use only tape on a gas connection (dope is required).
How do I avoid leaks at pipe connections?
Common leak causes: (1) insufficient thread sealant, (2) stripped or damaged threads, (3) cross-threaded fitting, (4) not tightening enough (hand-tight plus ¾ turn with a wrench for NPT), (5) over-tightening, which can crack the fitting or distort threads. Use the correct wrench size (two wrenches: one to hold the fitting, one to turn the connector) to apply even force without stripping. Tighten incrementally and check for leaks. If a joint weeps after tightening, tighten a bit more; if it still leaks after two full turns, unthread, re-seal, and re-thread.

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