Black steel pipe is ordinary carbon steel pipe with no zinc coating. The “black” is the dark oxide surface left from manufacturing, and the pipe is most often used for natural gas and propane lines, fire sprinkler systems, steam and compressed air, and as a cheap structural tube for posts, rails and frames.
Galvanized pipe is the same steel pipe with a hot-dipped zinc coating. Below is how black pipe is made and specified, where it is and is not a good fit, and how it compares with galvanized pipe.
What Black Steel Pipe Is
In the US, black pipe for building work is commonly made to ASTM A53, the common specification for welded and seamless steel pipe. A53 covers both finishes. The Wheatland Tube ASTM A53 Type E Grade B submittal sheet (checked October 2026) describes its product as black and hot-dipped galvanized welded pipe “intended for mechanical and pressure applications” and acceptable for ordinary uses in steam, water, gas and air lines.
The same sheet lists the A53 Grade B minimums that apply to black and galvanized pipe alike:
| Property (A53 Grade B, per Wheatland) | Value |
|---|---|
| Minimum yield strength | 35,000 psi |
| Minimum tensile strength | 60,000 psi |
| Maximum carbon | 0.30% |
| Maximum manganese | 1.20% |
| Wall thickness tolerance | Not more than 12.5% under nominal |
| Weight tolerance | Within 10% of the listed weight |
The letters in the A53 name tell you how the pipe was made: Type E is electric-resistance welded, Type F is furnace (continuous) welded and Type S is seamless. Grade A and Grade B are two strength levels.
Why it is called black
Hot-formed steel comes out of the mill with a thin, dark iron oxide layer, the same mill scale seen on structural shapes. Mills may also apply a light oil or varnish to slow rust in storage. That coating is temporary and is not corrosion protection for service; black pipe will rust when it is wet.
Black Pipe Sizes and Weights
Black pipe is sold by nominal pipe size (NPS) and schedule. Schedule 40 is the everyday weight; Schedule 80 is the heavier wall used where more strength or thread depth is needed. Values below are from the Wheatland submittal sheet for plain-end black pipe and agree, within rounding, with the AISC Shapes Database v16.0 (checked October 2026).
| NPS | OD (in) | Sch 40 wall (in) | Sch 40 (lb/ft) | Sch 80 wall (in) | Sch 80 (lb/ft) |
|---|---|---|---|---|---|
| 2 | 2.375 | 0.154 | 3.66 | 0.218 | 5.03 |
| 2-1/2 | 2.875 | 0.203 | 5.80 | 0.276 | 7.67 |
| 3 | 3.500 | 0.216 | 7.58 | 0.300 | 10.26 |
| 4 | 4.500 | 0.237 | 10.88 | 0.337 | 15.00 |
| 5 | 5.563 | 0.258 | 14.63 | 0.375 | 20.80 |
| 6 | 6.625 | 0.280 | 18.99 | – | – |
| 8 | 8.625 | 0.322 | 28.58 | – | – |
The Wheatland sheet lists Schedule 80 only through NPS 5, so the 6 and 8 cells are left blank here. Note that a “2-inch” pipe is 2.375 in outside; the nominal size is a name, not a measurement. To check the weight of any size, our steel tubing weight calculator works for pipe if you enter the outside diameter and wall.
Black Pipe vs Galvanized Pipe
Galvanized A53 pipe is hot-dipped in molten zinc after it is made. Wheatland’s sheet requires an average zinc coating of not less than 1.8 oz per square foot of surface, inside and outside, and warns that bending the pipe far enough to stretch or compress the zinc beyond its elastic limit can make some of the coating flake. Our guide to what galvanized steel is explains how the zinc protects the steel underneath.
| Black pipe | Galvanized pipe | |
|---|---|---|
| Steel | A53 carbon steel | Same A53 carbon steel |
| Surface | Bare, dark oxide; may be lightly oiled | Hot-dip zinc inside and out |
| Corrosion resistance | Low; rusts when wet | Much better outdoors and in damp areas |
| Welding | Straightforward | Zinc must be removed or ventilated |
| Cost | Lower | Higher |
| Common uses | Indoor gas lines, sprinklers, steam, air, structural posts | Outdoor railings, fences, exposed supports, some exterior gas runs |
Where Black Pipe Is Used
Natural gas and propane
Threaded black steel pipe is one of the most familiar materials for building gas piping. Fuel gas codes set the minimum. For example, Minnesota’s amendments to the International Fuel Gas Code, rule 1346.5403 (checked October 2026), say steel and wrought-iron gas pipe shall not be lighter than Schedule 40 and must comply with ASME B36.10, ASTM A53 or ASTM A106. The same rule says steel pipe exposed in exterior locations shall be galvanized or coated with an approved corrosion-resistant material.
Gas rules differ by state and city, and gas piping work usually needs a permit and a licensed installer. Check the code your jurisdiction has adopted before choosing a pipe material.
Fire sprinklers, steam and compressed air
Wheatland states that its A53 pipe in sizes 1 in through 6 in is UL Listed and FM Approved for fire sprinkler applications, and the A53 scope covers steam and air lines. In each case the system designer and the governing standard decide the schedule, joining method and any coating.
Structural and DIY uses
Black pipe is also used for handrails, shelving frames, sign posts, short columns and bollards, because it is cheap, widely stocked and easy to weld. It is the same idea as a lally column or a round HSS section, but A53 pipe is specified for pressure and mechanical service rather than as a structural column. Anything that will carry a floor, roof or beam load needs to be sized and checked by a licensed structural engineer, who will also decide whether pipe or structural tube is appropriate.
Where Black Pipe Is a Poor Fit
- Outdoors without a coating. Bare black pipe left in the weather rusts. Paint it, or use galvanized pipe, and follow any local code requirement for exterior gas pipe.
- Buried without protection. Steel in contact with soil needs a corrosion protection system chosen by the designer.
- Anywhere a local code names a different material. Potable water, drainage and gas each have their own approved-material lists, which vary by jurisdiction.
Painting and Protecting Black Pipe
If you want black pipe to last outdoors, clean off the oil and any loose scale, then prime and paint it. A rust-inhibiting primer under an exterior topcoat is the usual approach; our guide to rust prevention coatings compares the options. For gas piping, check whether your local code has its own marking or coating rules.
Black Steel Pipe FAQ
What is the difference between black pipe and galvanized pipe?
Only the surface. Both are usually ASTM A53 carbon steel pipe; galvanized pipe has a hot-dipped zinc coating inside and out, and black pipe does not.
Does black steel pipe rust?
Yes. The dark finish is oxide scale and sometimes a light oil, not a protective coating. Indoors and dry it lasts a long time; outdoors it needs paint or galvanizing.
Can black pipe be used for gas?
Yes, it is widely used for natural gas and propane. Codes such as Minnesota’s fuel gas rules require at least Schedule 40 steel pipe to ASTM A53, ASTM A106 or ASME B36.10. Always follow your local code and permit rules.
Can you weld black steel pipe?
Yes. A53 pipe is described by its maker as suitable for welding, threading and grooving. Clean off oil and scale at the joint first. Welding galvanized pipe takes more care; see our guide to welding galvanized steel.
How much does 2-inch black pipe weigh?
Schedule 40 NPS 2 black pipe weighs 3.66 lb/ft, so a 20 ft length weighs about 73 lb. Schedule 80 is 5.03 lb/ft.
Reference information only, not engineering advice. Disclaimer.