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A stainless steel pipe is a hollow cylindrical length of steel alloyed with chromium — at least 10.5% — so it resists rust and corrosion far better than carbon steel. You see it in process plants, on ships, in food lines, and inside buildings. The chromium forms a thin passive film on the surface. When that film is damaged, it reforms automatically in the presence of oxygen, which is why stainless stays cleaner longer than regular pipe.

We differentiate pipe from tube by usage more than by shape. Pipe is sized by nominal diameter and schedule — that is, by what fits standard fittings and valves. Tube is sized by actual outer diameter and wall thickness, and it is the go-to when you are bending, structural, or fitting it into a tight assembly. Both are round. Both come in seamless and welded. Both can be 304, 316, or something more specialized. The difference is in how you buy it and how you join it.

Stainless pipe is sold by nominal bore, schedule, and length. Nominal bore is a label, not the actual diameter. The outside diameter is fixed for a given NPS, and the wall thickness grows with schedule number. That is why a NPS 4 SCH 40 and a NPS 4 SCH 80 have the same OD but very different weights and pressure ratings.

Below is a quick reference for common sizes in SCH 10s through SCH 160s. The weights are for 304/316 (density 7.93 g/cm³). For 430, knock about 3% off. For duplex 2205, add about 1%.

NPS (inch)	OD (mm)	SCH 10s WT (mm)	Weight kg/m	SCH 40s WT (mm)	Weight kg/m	SCH 80s WT (mm)	Weight kg/m
1/2	21.3	1.65	0.97	2.77	1.56	3.76	2.09
3/4	26.7	1.65	1.26	2.87	1.99	3.91	2.65
1	33.4	1.91	1.81	3.38	3.10	4.55	4.09
1 1/2	48.3	2.11	2.88	3.68	4.89	5.08	6.58
2	60.3	2.11	3.74	3.91	6.62	5.54	9.14
3	88.9	2.77	6.75	5.49	12.6	6.35	14.3
4	114.3	3.05	9.63	6.05	18.0	8.05	23.5
6	168.3	3.40	15.5	7.11	30.5	10.97	45.6
8	219.1	4.78	29.7	8.18	48.9	12.70	72.7
10	273.1	5.08	40.0	9.27	69.6	15.09	108
12	323.9	6.35	58.5	11.07	97.4	17.48	149
18	457.2	6.99	84.7	13.49	158	21.44	242
24	609.6	8.74	149	17.48	287	26.19	417

To estimate weight without a table, use this formula for meters per kilogram by dividing the square of the OD in mm by the wall in mm, then multiplying by 0.02466. For a quick yard estimate, a NPS 4 SCH 40 304 pipe runs about 18 kg per meter, and a NPS 8 SCH 40 runs about 49 kg per meter.

When you order stainless pipe, the standard tells the mill what to check and what tolerances to hold. Mismatched standards are a common source of surprise on site.

Standard	Scope	Typical use
ASTM A312	Seamless and welded austenitic chromium–nickel stainless steel pipe	Process, power, chemical, oil & gas
ASTM A269	Seamless and welded austenitic stainless steel tubing for general service	Heat exchangers, condensers, structural
ASTM A213	Seamless ferritic and austenitic alloy-steel furnace tubes	Boilers, heat exchangers, superheaters
EN 10216-2	Pressurised purposes — non-alloy and alloy steel pipes	European projects, PED compliance
EN 10217-2	Welded steel pipes for pressure purposes	European welded pipe spec
JIS G3459	Stainless steel pipes for general structure	Japanese equipment and plant
ASME B36.19	Dimensional table for stainless pipe	Reference for NPS and SCH sizes

This is the decision that affects price and performance the most.

Feature	Seamless	Welded (ERW / Austenitic)
How it is made	Pilger mill or extrusion from a solid billet	Formed and welded along a longitudinal seam
Homogeneity	No seam, uniform cross-section	Weld zone is a metallurgical difference to manage
Pressure rating	Generally higher for a given size and schedule	Good, but the seam is the weak point under extreme cyclic load
Surface quality	Inside can be rougher unless reamed	Smooth inside and out after finishing
Size range	Up to about 323.9 mm OD as standard, larger on request	Wide range, up to 1219 mm OD and beyond
Cost	Higher, because of more processing	Lower, especially in larger diameters
Lead time	Longer for non-stock sizes	Shorter for standard sizes

Seamless is the default for high pressure, high temperature, and aggressive service. Think hydraulic lines, boiler tubes, and chemical process piping. Welded austenitic pipe is what you see in food, water, architecture, and general plant service where the pressure is moderate and the inside finish matters. If you are unsure, ask us which route fits your pressure, temperature, and fluid. The right choice is rarely the most expensive one.

The grade sets corrosion resistance and strength. Here is what we keep in coil, plate, and pipe form, and where each one belongs.

Grade	Type	Key features	Best for	Avoid
304 / 304L	Austenitic	18% Cr, 8% Ni, low carbon L version	General process, food, architecture. The default pipe grade.	Heavy chlorides, marine immersion
316 / 316L	Austenitic, 2–3% Mo	Molybdenum boosts resistance to chlorides and many acids	Coastal, chemical, pharma, offshore, desalination	Warm stagnant seawater (step up to duplex)
321	Austenitic, Ti-stabilized	Titanium prevents intergranular corrosion after welding	High temperature exhaust, continuous heat up to about 800°C	Cold general service where 304L is cheaper
310S	Austenitic, high Cr/Ni	Excellent heat and oxidation resistance	Furnace parts, heat exchangers, annealing boxes	Routine piping (over-spec and pricey)
2205 (duplex)	Duplex	Roughly twice the yield of 304, good chloride resistance	Oil & gas, chemical, seawater cooling, pulp & paper	Light-duty indoor use (cost not justified)
2507 (super duplex)	Duplex, higher alloy	Superior stress-corrosion and pitting resistance	Severe offshore, sour service, high chloride plants	Non-corrosive service
904L	Austenitic, super-austenitic	Very high alloy for aggressive acids	Sulfuric, phosphoric, acetic acid service	General water service
430	Ferritic, no nickel	Magnetic, cheaper, decent atmospheric resistance	Decorative, dry indoor, exhaust trim	Wet, food-contact, or exterior marine

304L and 316L are the low-carbon versions. The ‘L’ means carbon is capped at 0.03% instead of 0.08%, which reduces the risk of sensitization when you weld. If the pipe will be welded in service or during installation, spec the L grade. If it stays bolted or mechanically joined, regular 304 or 316 is fine.

The finish affects hygiene, pressure drop, and appearance. Inside finish matters most for process and food piping. Outside finish matters for architecture and exposed plant.

• Mill finish: As-produced. Industrial use only.
• Pickled: Acid treated to remove scale after annealing. The standard for process pipe.
• Bright annealed: Heated in a controlled atmosphere so no scale forms. Very clean, good for food and pharma.
• Ground outside: For visible architectural pipe where weld seam and scale must be removed.
• Polished inside and out: For sanitary process lines. Ra values are specified per client request.

For drinking water and food, pickled or bright annealed is usual. For chemical service, pickled is enough unless the product is very sensitive. For architecture, ground or polished gives the look people expect.

• Corrosion resistance without paint or coating in most environments.
• High strength to weight, especially duplex grades, which lets you use thinner walls.
• Clean surface that resists biofilm buildup in food and pharma lines.
• Long service life with low maintenance, often decades in the right grade.
• Weldable with standard TIG and MIG methods across the austenitic range.
• Heat and cold resistant, so the same pipe can serve process and cryogenic service.
• Recyclable at end of life with no loss of properties.

Sector	Typical service	Common grade
Oil & gas	Gathering lines, produced water, offshore	316L, 2205, 2507
Chemical & pharma	Process piping, CIP lines, acid transfer	316L, 904L, 2205
Food & beverage	Dairy, brewery, bottling, sanitization	304L, 316L, bright annealed
Power generation	Boiler feed, condenser, superheater	304H, 321, 310S
Marine & offshore	Seawater cooling, ballast, deck piping	316L, 2205
Construction	Handrails, structural, facade support	304, 316, ground finish
Water treatment	Desalination, reverse osmosis, effluent	316L, duplex
Pulp & paper	Black liquor, bleach plant, digesters	2205, 2507, 904L

One practical note on marine and desalination service: 316L is good, but warm, stagnant, or high-chloride water will attack it over time. Duplex 2205 or super duplex 2507 is the usual step up, and it cuts weight because you can use a thinner wall for the same pressure rating. That is the same logic we apply when we move from 304 to 316 on the equipment side, as explained in our 304 vs 316 brewery tank comparison.

We make the steel and we make the equipment, so the pipe you buy is the same material our tank division fabricates. That traceability matters when a spec fails and you need to know where the heat came from. We stock 304, 316L, 321, 2205, 2507 and 904L in common sizes, cut and process to order, and ship against EN 10204 3.1 mill certificates with PMI verification. If you are already buying cold rolled stainless sheet, hot rolled plate, or 304, 316, 430 sheet from us, the pipe comes from the same mill relationship. Browse the full catalogue at all products or the stainless steel category.

A lot of the pipe we ship ends up as the skeleton of a larger system. Our sister company builds stainless equipment, and the stainless steel tanks they make, from fermentation tanks to jacketed mixing tanks and heating and cooling tanks, are fabricated from the same 304 and 316L pipe and sheet we stock. If you need the material and the fabricated vessel from one source, that is the setup we offer. The 304 vs 316 brewery tank piece on the equipment side goes into the molybdenum and chloride reasoning in more detail.

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