Process piping and plumbing look alike from the outside. Both move fluid through pipe. In practice they are two separate disciplines, built to different codes, by different trades, with very different consequences when they fail. Plumbing keeps a building livable: clean water in, waste water out. Process piping is part of the plant itself, carrying the chemicals, steam, and gases a facility needs to make its product. Treat the two as interchangeable on an industrial project and you invite rework, failed inspections, and real safety risk.
Key Takeaways
- Different jobs. Plumbing serves the building (potable water, sanitary waste, venting). Process piping serves the process (chemicals, steam, compressed gas, hydrocarbons).
- Different codes. Plumbing follows model plumbing codes adopted by your state or city. Process piping follows ASME B31.3 and the wider ASME B31 family.
- Different trades. Licensed plumbers install building systems. Pipefitters and steamfitters build process systems under a mechanical contractor.
- Different stakes. Federal law treats process piping as safety-critical equipment when it carries a highly hazardous chemical, so documentation and testing are not optional.
- Different hire. For a bathroom or a service line, call a plumber. For a compressor station, data center loop, or chemical line, call a process piping contractor.
Process piping vs plumbing: what is the real difference?
The U.S. Bureau of Labor Statistics draws the line by what the pipe carries. Its Occupational Outlook Handbook says plumbers “install and repair water, gas, and other piping systems in homes, businesses, and factories,” while pipefitters and steamfitters “install and maintain pipes that may carry chemicals, acids, and gases,” mostly in manufacturing, commercial, and industrial settings (U.S. Bureau of Labor Statistics). The BLS groups all three trades together and counted 510,600 of them in 2025, yet the day-to-day work splits cleanly.
Plumbing is building service. It delivers potable water to fixtures, carries sanitary waste to the sewer, and vents the drain system so it drains correctly. The pipe exists to make a space usable by people, and it stops at the point where a building system ends.
Process piping is the opposite mindset. The pipe is a working part of an industrial process, moving a fluid so it can be heated, cooled, compressed, reacted, measured, or blended. When that line runs to a compressor, a heat exchanger, a reactor, or a data center cooling plant, its temperature, pressure, and chemistry are engineered to a specification. That is why the discipline sits with mechanical contractors and their pipefitters rather than with the plumbing trade.
Which codes govern process piping vs plumbing?
The scope of the process piping code is explicit. ASME B31.3 “contains requirements for piping typically found in petroleum refineries; chemical, pharmaceutical, hydrogen, textile, paper and pulp, power generation, semiconductor, and cryogenic plants,” and it covers the materials and components, design, fabrication, assembly, erection, examination, inspection, and testing of that piping (ASME). It is one book in a larger set. ASME B31.1 covers power piping in boilers and turbines, B31.3 covers process piping inside a plant, and B31.8 covers gas transmission and distribution. Engineers pick the book that matches the service.
Plumbing answers to a different rulebook entirely. Building plumbing is governed by a model plumbing code, most often the International Plumbing Code or the Uniform Plumbing Code, which each state or municipality adopts and then enforces through local permits and inspectors. Those codes are written around health and sanitation: backflow prevention, fixture counts, trap seals, and drain slopes.
Pick the right book first
Three ASME codes, and the service each one covers
A single facility can contain all of these plus building plumbing. The engineer picks the book that matches the service before a drawing is issued.
B31.1
power piping: boilers and turbines
B31.3
process piping inside a plant: refineries, chemical, pharmaceutical, hydrogen, paper, power, semiconductor and cryogenic
B31.8
gas transmission and distribution
The practical result is that a single facility can contain both. The restroom and the eyewash station are plumbing. The nitrogen header, the steam main, and the chemical feed lines are process piping. Knowing which code applies to which line is the first thing a competent mechanical and process piping team settles before a drawing is issued.
Why the code difference changes how the work is inspected
Federal law treats process piping as safety-critical equipment. OSHA’s Process Safety Management standard lists “Piping systems (including piping components such as valves)” among the equipment whose mechanical integrity an operator must maintain, and that duty applies to any process holding a highly hazardous chemical at or above the threshold quantities in the standard’s Appendix A (29 CFR 1910.119) (OSHA). Appendix A sets that trigger at 10,000 pounds for anhydrous ammonia and at 100 pounds for phosgene.
That legal weight changes the paperwork. Process piping in hazardous service is documented from material through final test: mill certifications for the pipe, welder qualification records, nondestructive examination such as radiography on a defined percentage of welds, and a pressure test proved and recorded before the system is handed over. A leak in a building drain is a maintenance call. A leak in a process line can be a reportable release.
Plumbing inspection is real, but it is scaled to building safety rather than process safety. A local inspector checks that the rough-in matches the plumbing code and that the system holds a pressure or water test. There is no federal mechanical integrity program sitting behind a residential water line, because the failure mode is property damage, not a chemical release.
Materials, welding, and testing: how the fabrication differs
Look at how each system is joined and the split becomes obvious. Plumbing runs on copper, PEX, PVC, and cast iron, assembled with soldered joints, solvent-welded fittings, press connections, and threads. Most of it is installed in place, in the building, by the plumber who will also test it.
Process piping runs on carbon steel, stainless steel, and specialty alloys, welded to a qualified procedure and examined to ASME B31.3. Much of it is never welded at the job site at all. Instead it is built in a shop as pipe spools, prefabricated assemblies of pipe, fittings, and flanges made to an isometric drawing and shipped as one piece. Building the spool in a controlled bay improves weld quality, lets testing happen before the piece ever ships, and collapses field time down to setting, bolting, and tie-in. That is the core argument for pipe spool fabrication and the reason so much process work is split between shop and field fabrication.
The equipment and the stamps tell you whether a fabricator is set up for this. LMC fabricates carbon and stainless pipe spools, cuts and processes steel on a PythonX CNC plasma system and Ficep Gemini plate processors, and holds ASME “U,” “S,” and “PP” stamps, an NBIC “R” for repairs, API 1104 for pipeline welding, and AWS D1.1 and D1.5 for structural and bridge welding. Hydro and pneumatic testing is self-performed, so system verification does not wait on a third party. None of that vocabulary appears on a plumbing job, because a plumbing job does not need it.
Who should you hire: a plumber or a process piping contractor?
Start with the trade math. The Bureau of Labor Statistics projects about 42,000 openings a year for plumbers, pipefitters, and steamfitters over the 2025 to 2035 decade, against a median wage of $63,800 in May 2025 (U.S. Bureau of Labor Statistics). Skilled pipe crews are in short supply, so the real question is not price per hour. It is whether the contractor you hire actually holds the qualifications your system demands.
If the job is a building system, potable water, sanitary drainage, a gas service line, or fixtures, hire a licensed plumber. That is exactly what the plumbing code and the plumbing license exist to cover.
If the job is a process, hire an industrial mechanical contractor that builds process piping for a living. Compressor stations and metering and regulating stations in oil and gas, chemical and food and pharmaceutical process lines, and the mechanical loops behind power generation and data centers all live under ASME B31.3, not the plumbing code. LMC Industrial Contractors was founded in 1982 as a mechanical contracting company specializing in process piping, and now fields more than 350 tradespeople out of a fabrication facility in Dansville, New York with over 700,000 square feet of covered space on 88 acres. The self-perform model matters here: when the same company welds the spool, sets it, tests it, and documents it, the schedule and the quality record stay under one roof rather than splitting across subcontractors.
Frequently Asked Questions
Is process piping the same as plumbing?
No. Plumbing carries potable water, sanitary waste, and venting for a building and follows a model plumbing code. Process piping carries the fluids used in an industrial process and follows ASME B31.3. They use different materials, different joining methods, and different inspections.
What code covers process piping?
In the United States, process piping is most commonly designed and built to ASME B31.3, the Process Piping code. It sits alongside ASME B31.1 for power piping and B31.8 for gas transmission and distribution. The engineer selects the code that matches the service and pressure.
Can a licensed plumber install process piping?
Usually not, and not because of skill alone. Process piping in industrial service requires welders qualified under ASME Section IX, fabrication and examination to ASME B31.3, and often the documentation demanded by OSHA’s Process Safety Management standard. Those qualifications sit with pipefitters and mechanical contractors rather than with a plumbing license.
What industries rely on process piping?
Petroleum refineries, chemical and pharmaceutical plants, hydrogen and cryogenic facilities, pulp and paper, semiconductor fabs, power generation, and data centers all depend on process piping, per the scope of ASME B31.3. Anywhere a fluid is part of the process rather than a building service, the work is process piping.
Process piping and plumbing both matter, but they are not the same purchase. Match the code, the trade, and the qualifications to the fluid your system carries. When the fluid is part of an industrial process, LMC Industrial Contractors can fabricate and install it to code and prove it with the documentation the job requires. Reach the team at (585) 335-3131 or lmcinfo@lmcic.com to scope a project.
