The Complete Guide to Pipe Marking: ASME/ANSI A13.1 Explained
Walk into any commercial building or industrial facility and you'll see labels on the pipes. Some are green. Some are yellow. Some have arrows on them.
But what do they all mean?
That's what this guide is for.
Pipe marking keeps workers safe. It helps emergency responders act fast. It helps inspectors pass your job. And it's required on most commercial and industrial projects.
Let's break it all down.
What Is Pipe Marking?
Pipe marking is the practice of putting labels on pipes to show what's inside them. The labels tell you:
- What fluid or gas is in the pipe
- Which direction it flows
- Whether the contents are safe or dangerous
Think about walking into a mechanical room with 50 pipes. Without labels, you have no idea what's in any of them. With labels, you can instantly tell which pipe carries natural gas, which one carries potable water, and which one is the fire sprinkler line.
That information could save your life.
Why Pipe Marking Matters
There are three main reasons pipe marking is required on most jobs:
Safety. Workers need to know what they're dealing with before they open a valve or cut into a pipe. A label that says "Acid" tells you to grab your protective gear first.
Emergency response. When firefighters enter a building, they need to know which pipes carry fuel and which carry water. Seconds matter in an emergency.
Compliance. Most facilities are required by code or insurance to label their pipes. An unmarked pipe system can fail inspection and delay your project.
The Standard: ASME/ANSI A13.1
The main pipe marking standard in the United States is ASME A13.1. It's published by the American Society of Mechanical Engineers (ASME).
ASME A13.1 covers:
- What colors to use for different pipe contents
- How big the labels need to be based on pipe size
- Where to place labels along the pipe
- What information must appear on the label
The standard is widely accepted across commercial, industrial, and institutional facilities. It's referenced in building codes, OSHA regulations, and facility safety programs across the country.
Quick Note: ASME A13.1 is a voluntary standard, not a federal law. But OSHA, many building codes, and most commercial contracts require it. In practice, most facilities treat it as mandatory.
ASME A13.1 Color Codes at a Glance
The most important thing ASME A13.1 does is assign colors to pipe contents based on how hazardous they are.
| Color Combination | What It Means | Common Examples |
|---|---|---|
| Green / White | Safe fluids | Potable water, chilled water, filtered water |
| Yellow / Black | Hazardous materials | Acids, corrosives, flammable liquids |
| Red / White | Fire suppression | Fire sprinkler water, fire protection lines |
| Orange / Black | Toxic / extra hazardous | Ammonia, toxic gases, extreme hazard chemicals |
| Blue / White | Low-hazard compressed gases | Compressed air, nitrogen, argon |
| Brown / White | Combustible fuels | Natural gas, fuel oil, diesel |
| Purple / White | Reclaimed / non-potable water | Recycled water, gray water |
We go much deeper on colors in our [Pipe Marker Color Code Guide →] — but this chart gives you the basic framework.
What Information Goes on a Pipe Label?
A compliant pipe marker needs to include:
- The name of the contents — written in plain English (e.g., "Natural Gas" or "Chilled Water Supply")
- Flow direction arrows — showing which way the fluid or gas is moving
- The correct background color — based on the ASME A13.1 chart above
Some labels also include pressure ratings, temperature information, or hazard warnings. Those aren't always required, but they can be helpful for workers and inspectors.
How Big Does the Label Need to Be?
Label size is based on the outside diameter (OD) of the pipe. Here's the ASME A13.1 sizing chart:
| Pipe Outside Diameter (OD) | Label Size | Arrow Size |
|---|---|---|
| ¾" to 1¼" | 8" × 1⅛" | 2½" × ½" |
| 1½" to 2" | 8" × 1⅛" | 3" × ¾" |
| 2½" to 7⅞" | 14" × 2¼" | 5" × 1¼" |
| 8" to 10" | 24" × 4" | 6½" × 2½" |
| 10" and larger | 32" × 4" | 6½" × 2½" |
At Print Pro AZ, our pipe markers come in all five sizes to fit every pipe on your job. Shop pipe markers by size →
Where Do You Put the Labels?
ASME A13.1 gives specific rules for where labels go. You need to label pipes:
- At every valve — so workers know exactly what they're shutting off
- At every branch connection — wherever pipes split or join
- On both sides of walls, floors, and ceilings — so the label is always visible from either side
- Near every piece of equipment — at the connection point to the equipment
- At regular intervals on long straight runs — typically every 25 to 50 feet
Labels should be easy to read from the floor. Workers shouldn't need a ladder to identify a pipe.
Who Needs to Follow ASME A13.1?
Pipe marking applies in a wide range of facilities:
- Commercial buildings — offices, retail spaces, hotels
- Industrial facilities — factories, warehouses, processing plants
- Healthcare facilities — hospitals, clinics, surgery centers
- Schools and universities
- Government buildings
- Power plants and utility facilities
If a building has a mechanical room with multiple pipe systems, it almost certainly needs pipe markers.
OSHA and Pipe Marking
OSHA doesn't have one single, all-in-one pipe marking standard. But a few OSHA regulations do address it:
- 29 CFR 1910.261 — covers pipe marking in pulp, paper, and paperboard mills
- 29 CFR 1910.119 — process safety management for highly hazardous chemicals
- General Duty Clause — OSHA can cite employers for known safety hazards, including unmarked pipes
In most cases, following ASME A13.1 satisfies OSHA's expectations for pipe identification. We cover this in more detail in our [OSHA Pipe Marking Requirements Guide →].
Common Pipe Marking Mistakes
Here are the mistakes we see most often on job sites:
Wrong color. Using green/white on a chemical line instead of yellow/black. This is a safety risk and an inspection failure.
Too small. Using an 8" label on a 10" pipe. The label size has to match the pipe size per ASME A13.1.
No flow arrows. The arrows show which way the fluid is moving. Don't skip them — they're required.
Too few labels. Marking only one spot on a long pipe run. You need labels at every valve, branch, wall penetration, and at regular intervals.
Faded or peeling labels. Using indoor labels on an outdoor or sun-exposed pipe. Always use UV-resistant labels for outdoor applications.
Why Label Material Matters
Not all pipe markers are the same. The right material depends on where the pipe is located:
- Vinyl — great for indoor pipes in dry environments
- UV-resistant vinyl — required for outdoor pipes or any sun-exposed location
- Polyester — ideal for harsh chemical environments or extreme temperatures
At Print Pro AZ, our pipe markers are made with UV-resistant, self-adhesive vinyl that holds up in Arizona's intense heat and sun. They apply fast with double-sided tape and stay put through inspections and the life of the installation.
How to Get Started
Pipe marking a facility from scratch can feel like a big job. Here's a simple process to follow:
- Walk the facility and list every pipe system you can find
- Identify the contents of each pipe system
- Look up the correct color using the ASME A13.1 color chart
- Measure your pipe ODs so you pick the right label size
- Mark every valve, branch, and wall penetration first, then label straight runs at regular intervals
- Order your labels — standard markers or custom, depending on your pipe contents
If you have non-standard pipe contents — anything not covered by a standard label — you can order custom pipe markers with any text you need.
Ready to Label Your Pipes?
At Print Pro AZ, we stock 235+ standard pipe markers that cover virtually every common pipe system. Same-day shipping. Made in the USA. ASME A13.1 compliant.
👉 Shop All Pipe Markers → 👉 Need something custom? Order Custom Pipe Markers →
Frequently Asked Questions
What is ASME A13.1? ASME A13.1 is the main pipe marking standard in the United States. Published by the American Society of Mechanical Engineers, it covers the colors, sizes, and placement requirements for pipe markers.
Is pipe marking required by law? ASME A13.1 is a voluntary standard, but most commercial and industrial facilities are required to follow it through their state building code, OSHA regulations, insurance requirements, or project specifications.
What colors are used on pipe markers? The colors depend on what's in the pipe. Green/white is for safe fluids like water. Yellow/black is for hazardous materials. Red/white is for fire suppression systems. Orange/black is for toxic or extra-hazardous materials. Brown/white is for fuels. Blue/white is for low-hazard compressed gases.
How often do pipes need to be labeled? ASME A13.1 requires labels at every valve, branch connection, wall or ceiling penetration, and near equipment. For straight runs, labels should appear at regular intervals — typically every 25 to 50 feet.
What size pipe marker do I need? Label size depends on your pipe's outside diameter (OD). Pipes under 1¼" OD use an 8"×1⅛" label. Pipes between 2½" and 7⅞" OD use a 14"×2¼" label. Larger pipes use 24" or 32" labels. See the full size chart above.
Do pipe markers need to wrap all the way around the pipe? No. ASME A13.1 doesn't require full wrap. The label just needs to be clearly visible from normal viewing angles during regular operations.