Stainless Steel Pipe & Tube Supplier | ASTM A312

Bundled stainless steel pipes of varying diameters racked in a mill warehouse

Close-up of a stainless steel pipe end showing the weld seam and polished bore

Walmay is a stainless steel pipe manufacturer and exporter supplying seamless and welded pipe in 304, 304L, 316, 316L, 321, 310S, 904L and 2205 duplex. We cover NPS 1/2 to NPS 24 in schedules 5S through 80S to ASTM A312 and ASME SA312, plus outside diameters from 6 mm to 630 mm in metric sizes, cut to length and supplied with EN 10204 3.1 mill test certificates. Round, square and rectangular sections are all held, and material can be polished, pickled or bright annealed before it ships.

Stainless Steel Pipe and Tube We Stock

Grade	Route	Standard	Size range	Typical service
304	Seamless and welded	ASTM A312	NPS 1/2-24	General process, water, structural, food
304L	Seamless and welded	ASTM A312	NPS 1/2-16	Welded process lines without post-weld anneal
316	Seamless and welded	ASTM A312	NPS 1/2-24	Marine, coastal, chemical transfer
316L	Seamless and welded	ASTM A312	NPS 1/2-24	Pharmaceutical, sanitary, chloride service
316Ti	Seamless	ASTM A312	NPS 1/2-12	Welded assemblies held at 400-800 C
321	Seamless	ASTM A312	NPS 1/2-12	Exhaust, superheater, expansion joints
310S	Seamless and welded	ASTM A312	NPS 1/2-12	Furnace and kiln service to 1,050 C
904L	Seamless	ASTM B677	NPS 1/2-10	Sulphuric and phosphoric acid lines
2205 duplex	Seamless and welded	ASTM A790	NPS 1/2-16	Offshore, brine, heat exchangers
410	Seamless	ASTM A268	NPS 1/2-8	Wear and abrasion service
430	Welded	ASTM A268	NPS 1/2-6	Indoor decorative, appliance work

Form-specific datasheets cover seamless pipe, square tube, rectangular tube, precision bright tube and 201 decorative welded pipe.

Pipe or Tube: Which One Should You Order

The two words are not interchangeable and ordering the wrong one is the most common cause of a rejected delivery. Pipe is specified by nominal pipe size and schedule, where NPS is a label rather than a measurement and the wall thickness comes from the schedule. Tube is specified by actual outside diameter and actual wall thickness, and is held to tighter dimensional and surface tolerances because it carries a mechanical or hygienic function.

Enquiries reach us in every possible wording. Some ask for stainless steel tube, steel that is drawn or welded to a tube tolerance. Others ask for stainless tube, steel supplied to an outside diameter rather than a schedule. When the request is for pipe, stainless steel suppliers quote by NPS and schedule, so a request for a stainless steel round tube in 2 inch usually means 60.3 mm outside diameter once it is translated into pipe language.

You specify	Pipe	Tube
Diameter reference	Nominal pipe size, NPS	Actual outside diameter
Wall reference	Schedule 5S, 10S, 40S, 80S	Actual wall thickness or gauge
Governing standard	ASTM A312 for welded and seamless	ASTM A269 or A554
Tolerance	Looser, pressure driven	Tighter, dimensionally driven
Typical use	Process and utility piping	Heat exchangers, handrail, instrumentation, structures

Our guide to stainless steel pipes versus tubes works through the consequences for pressure rating, fittings and welding.

ASTM A312 and ASME SA312 Schedule Chart

Wall thickness in millimetres by nominal pipe size, to ASME B36.19M. The S suffix denotes the stainless series, which is thinner than the equivalent carbon steel schedule at the same NPS.

NPS	Outside diameter	SCH 5S	SCH 10S	SCH 40S	SCH 80S
1/2 in	21.3 mm	1.65	2.11	2.77	3.73
3/4 in	26.7 mm	1.65	2.11	2.87	3.91
1 in	33.4 mm	1.65	2.77	3.38	4.55
1-1/2 in	48.3 mm	1.65	2.77	3.68	5.08
2 in	60.3 mm	1.65	2.77	3.91	5.54
3 in	88.9 mm	2.11	3.05	5.49	7.62
4 in	114.3 mm	2.11	3.05	6.02	8.56
6 in	168.3 mm	2.77	3.40	7.11	10.97
8 in	219.1 mm	2.77	3.76	8.18	12.70

Pipe Weight per Metre and per 20 ft Length

Weights are calculated for austenitic grades at 8.0 g/cm3 in schedule 40S, the most commonly ordered wall. Use them for freight estimates and support spacing.

NPS	SCH 40S wall	Weight per metre	Weight per 20 ft length
1/2 in	2.77 mm	1.29 kg	7.9 kg
3/4 in	2.87 mm	1.72 kg	10.5 kg
1 in	3.38 mm	2.55 kg	15.5 kg
1-1/2 in	3.68 mm	4.13 kg	25.2 kg
2 in	3.91 mm	5.54 kg	33.8 kg
3 in	5.49 mm	11.51 kg	70.1 kg
4 in	6.02 mm	16.38 kg	99.9 kg
6 in	7.11 mm	28.80 kg	175.6 kg
8 in	8.18 mm	43.36 kg	264.3 kg

For any size the formula is weight in kg per metre equals 0.025133 multiplied by the wall thickness multiplied by the outside diameter minus the wall thickness, both in millimetres.

Seamless or Welded

Criterion	Seamless	Welded
Manufacture	Extruded or cold drawn from a billet, no weld seam	Formed from strip and longitudinally welded
Pressure service	Preferred for high pressure and cyclic duty	Suitable to design pressure with a weld joint factor
Wall uniformity	Slightly less uniform, thicker tolerance band	Very uniform, follows the strip thickness
Cost	Higher, especially above NPS 8	Lower, better availability in large diameters
Inspection	Ultrasonic or eddy current on the body	Weld seam tested by eddy current or hydrostatic test

Welded pipe is not a lesser product. For most water, gas and low-pressure process duties it is the economically correct answer, and above NPS 12 it is often the only practical one. Reach for seamless when the code requires it, when the service is cyclic or high pressure, or when a weld seam would interfere with downstream forming.

Sizes, Finishes and Tolerances

Parameter	Options
Nominal pipe size	NPS 1/2 to NPS 24
Metric outside diameter	6 mm to 630 mm
Wall thickness	0.5 mm to 30 mm
Schedules	5S, 10S, 20, 40S, 80S, and XS on request
Standard lengths	6 m, 6.096 m for 20 ft, or cut to length
Surface	Mill, pickled, 180 or 320 grit satin, bright annealed, No.8 mirror
Ends	Plain, bevelled to 30 degrees, threaded on request
Certification	EN 10204 3.1, hydrostatic and eddy current test reports

Square and rectangular hollow sections run from 10x10 mm to 300x300 mm and 20x10 mm to 400x200 mm respectively, in walls from 0.6 mm to 12 mm.

Bundled stainless steel pipes strapped and tagged for export shipment on a warehouse dock

Working Out the Allowable Working Pressure

Buyers frequently ask which schedule a given pressure needs. The answer comes from the ASME B31.3 wall thickness relationship rather than from a lookup table, because the allowable stress changes with grade and with design temperature.

The internal design pressure that a straight pipe can carry is given by P equals 2 S E W t divided by D minus 2 Y t, where S is the allowable stress for the grade at the design temperature taken from ASME B31.3 Table A-1, E is the quality factor, 1.0 for seamless and 0.85 for most longitudinally welded pipe, W is the weld joint strength reduction factor, t is the wall thickness after deducting the mill tolerance and any corrosion allowance, D is the outside diameter and Y is the temperature coefficient, 0.4 for austenitic steel below 480 C.

Three consequences matter when you place the order.

Deduct the mill tolerance before you calculate. ASTM A312 permits minus 12.5 percent on wall for seamless pipe, so a nominal 3.91 mm wall must be treated as 3.42 mm in the design case.
Welded pipe is penalised by the 0.85 quality factor, so at the same schedule it carries roughly 15 percent less pressure than seamless unless the weld is radiographed and a higher factor is justified.
Raising the design temperature reduces S sharply. Between 20 C and 400 C the allowable stress for 316L falls by roughly a third, which often moves the requirement up one schedule.

Send us the design pressure, design temperature, medium and code, and we will confirm the schedule rather than leaving the interpretation to the purchase order.

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Fittings, Flanges and Joining

Pipe and fittings must be specified to matching standards or they will not line up on site.

Component	Standard	Note
Butt weld fittings	ASME B16.9	Elbows, tees, reducers and caps matched to NPS and schedule
Socket weld and threaded fittings	ASME B16.11	Normally NPS 2 and below
Flanges	ASME B16.5 up to NPS 24	Class 150 to 2500, weld neck or slip on
Sanitary fittings	ASME BPE	Tri-clamp connections on tube outside diameter, not NPS
Compression fittings	Manufacturer specific	Requires tube tolerance, so order to ASTM A269 rather than A312

The last row is the one that catches buyers out. Instrumentation and compression fittings seal on the actual outside diameter, so they need tube ordered to a tube standard. Pipe supplied to ASTM A312 has a looser diameter tolerance and will not seal reliably in a compression fitting.

Standards We Supply To

Standard	Scope
ASTM A312 / ASME SA312	Seamless and welded austenitic pipe for corrosive and high-temperature service
ASTM A790	Seamless and welded ferritic-austenitic duplex pipe
ASTM A269	Seamless and welded austenitic tubing for general service
ASTM A554	Welded mechanical and structural tubing
ASTM A213	Seamless boiler, superheater and heat exchanger tube
ASTM A268	Seamless and welded ferritic and martensitic tube
EN 10216-5 / EN 10217-7	European seamless and welded stainless tube
JIS G3459	Japanese stainless steel pipe
NACE MR0175	Sour service material requirements where specified

Stainless steel pipe being cut to length on a bandsaw in a fabrication shop

Technician checking stainless steel pipe wall thickness with an ultrasonic gauge

What We Do Before It Ships

Processing in our own facility is described in full on the processing capabilities page.

Cut to length, including exact 20 ft and 6 m bundles
End bevelling for site welding and end facing for fittings
Polishing to 180 grit, 320 grit, satin or mirror
Pickling and passivation, and surface treatment for sanitary duty
Hydrostatic, eddy current and dye penetrant testing with reports
Bundling in wooden crates with end caps and moisture barrier

Applications

Chemical and petrochemical transfer lines in 316L, 904L and duplex, covered on our chemical production workshops page
Seawater intake, brine and reject lines for desalination plants
Boiler, superheater and condenser tube for energy production plants
Sanitary process piping for pharmaceutical and food production
Hull, deck and ballast systems in shipbuilding yards
Structural handrail, balustrade and frame work for public facilities

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Ordering, Lead Times and Pricing

Item	Detail
Minimum order	1 tonne from stock, 3-5 tonnes for mill-rolled sizes
Lead time from stock	7-12 days to loading
Lead time seamless mill run	30-45 days
Lead time welded mill run	20-30 days
Incoterms	FOB, CIF, DAP
Packing	Wooden crate or bundle, plastic end caps, edge protection

Send the grade, NPS or outside diameter, schedule or wall thickness, length, quantity, end preparation, surface finish and destination port. Pipe pricing tracks the nickel and molybdenum alloy surcharge, so quotations carry a validity window rather than a standing list price.

Why Buyers Choose Walmay

Compared with other stainless steel pipe suppliers we hold real tonnage rather than quoting against a mill order, and we finish the material before it leaves. Among stainless steel tube manufacturers and stainless steel tube suppliers serving export markets, the practical differences are stock depth, in-house cutting and polishing, and complete test documentation with every heat. Walmay has operated as a stainless steel pipe exporter for over eleven years to more than 100 countries; the company background is on our about us page.

Other forms: sheet and plate, bar and rod, coil and strip, profiles, or browse all stainless steel products.

FAQs

What is the difference between 304 and 316 stainless steel pipe?

Both are austenitic and handle similar pressures, but 316 contains two to three percent molybdenum, which markedly improves resistance to chlorides, seawater and reducing acids. Use 304 for general water, structural and food duty inland. Use 316 or 316L for coastal installations, brine, swimming pool plant and most chemical transfer. Where chloride levels and temperature are both high, move to 2205 duplex rather than paying for a thicker 316 wall.

How much does a 20 foot stainless steel pipe weigh?

A 20 ft length is 6.096 m. In schedule 40S austenitic material a 2 inch pipe weighs about 33.8 kg, a 4 inch about 99.9 kg and a 6 inch about 175.6 kg. For other sizes multiply 0.025133 by the wall thickness and by the outside diameter minus the wall thickness to get kilograms per metre, then multiply by 6.096.

Why isn't stainless steel used for plumbing?

It is, but mostly in commercial and industrial buildings rather than housing. Domestic plumbing favours copper, PEX and PVC because they cost less and need only simple joints, whereas stainless pipe normally requires welding or press fittings and a trained installer. Where water quality, fire performance or a fifty-year service life matter, stainless is the standard choice, and 316L is used throughout hospital, pharmaceutical and food plant piping for exactly those reasons.

What is the price of a 12-foot stainless steel pipe?

Pipe is priced by weight against the current nickel and molybdenum surcharge, then adjusted for grade, schedule, seamless or welded route, end preparation and quantity, so a length price only exists once the size is fixed. Send the NPS, schedule, grade and quantity with your destination port and we return a quotation valid for a stated period.

Do you supply seamless and welded pipe to ASTM A312?

Yes. Both routes are covered by ASTM A312 and ASME SA312 for austenitic grades, with duplex to ASTM A790. Every shipment carries an EN 10204 3.1 certificate with heat number, chemical analysis, mechanical results and the hydrostatic or eddy current test record.

What is the smallest and largest size you can supply?

Pipe runs from NPS 1/2 to NPS 24, and metric tube from 6 mm to 630 mm outside diameter with walls from 0.5 mm to 30 mm. Precision thin-wall requirements are met with 304 precision bright tube.

Can you cut pipe to length and bevel the ends?

Yes. We cut to your list, hold exact 6 m or 20 ft bundles, and bevel ends to 30 degrees for site welding or face them for fittings. Doing it at our end removes an operation and the offcut from your yard.

Do you supply square and rectangular tube as well as round?

Yes. Round is the largest part of our stock, but we also hold square tube from 10x10 mm to 300x300 mm and rectangular tube from 20x10 mm to 400x200 mm, mostly to ASTM A554 for structural and architectural work.

Which finish should I ask for on visible pipe?

For handrail and balustrade, 180 grit satin is the usual specification and hides handling marks well. For architectural feature work, 320 grit or mirror is used. For sanitary process lines the requirement is normally expressed as a surface roughness limit, commonly 0.8 micrometres Ra or better, achieved by bright annealing or mechanical polishing followed by passivation.