Stainless steel tube and pipe: grades, standards and forms

Stainless steel tube and pipe carries fluids, forms handrails and frames, and builds process and marine pipework, with the grade, the make (welded or seamless) and the standard all set by the duty. ULAMEX supplies stainless tube and pipe in 304, 316L and duplex 2205, round, square and rectangular, to the relevant EN standards, with a 3.1 certificate on request. This guide covers tube versus pipe, welded versus seamless, the grades, forms, standards and finishes.

Tube versus pipe

The two words are often used interchangeably, but there is a technical difference. Tube is specified by its outside diameter and wall thickness and is used for mechanical, structural and architectural work, where the exact outside dimension matters for fit and appearance. Pipe is specified by a nominal bore and a schedule (wall class) and is used to carry fluids under pressure, where the bore and pressure rating matter. ULAMEX supplies both, so a job that mixes handrail tube with process pipe is sourced together.

Welded versus seamless

Stainless tube is made two ways. Welded tube is formed from strip and welded along a seam, which covers the great majority of architectural, mechanical and general pressure work at a lower cost. Seamless tube is made without a seam, from a pierced billet, and is specified where the highest pressure or the most demanding service rules out a weld. For most tube and pipe, welded is the standard choice; seamless is the step up for critical pressure duty.

Grades for stainless tube

The grade is matched to the environment, exactly as for sheet and bar. ULAMEX supplies tube and pipe in the common austenitic and duplex grades.

For the full grade detail see our guides to 304 and 316 stainless steel and duplex 2205: 304 for general work, 316L wherever chlorides or food contact are involved, and duplex 2205 for high-pressure or severe marine pipework.

Forms: round, square and rectangular

Stainless tube is supplied in round, square and rectangular sections. Round tube covers handrails, balustrades, process and food pipework and heat-exchanger tube; square and rectangular tube cover frames, structural members and architectural work. Ornamental (decorative) tube is made to tight surface and dimensional standards for visible work, while pressure pipe is made to the pressure standards below.

Dimensions and how to specify

Tube is ordered by its outside diameter and wall thickness, for example 42.4 mm outside diameter by 2 mm wall, while pipe is ordered by nominal bore (DN or NPS) and schedule, which sets the wall for the pressure rating. Give the grade, the section (round, square or rectangular), the dimensions, the standard and the finish with an enquiry, and add the surface roughness for hygienic pipework, so the quotation and the delivered tube match the job first time. ULAMEX supplies tube and pipe in standard mill lengths.

Standards

The standard follows the application, and stating it on the order ensures the right product.

For hygienic food, dairy and pharmaceutical pipework, tube to EN 10357 with a polished internal surface, and 3-A sanitary practice, is the specification. For structural and architectural tube, EN 10296-2 mechanical tube covers the need.

Finishes

Tube is supplied from mill finish to polished. Mechanical and pressure tube is usually mill or pickled finish. Architectural and handrail tube is polished, commonly to a satin (brushed) finish around 320 grit or a brighter 400 grit, and mirror polished where a reflective surface is wanted. For hygienic pipework, the internal surface is polished to a controlled roughness so it cleans to standard. State the finish and, for hygienic tube, the surface roughness on the order.

Applications

Stainless tube and pipe serves several sectors. Architecture and construction use round and square tube for handrails, balustrades, canopies and frames, in 304 or 316 with a brushed or mirror finish. Food, dairy and pharmaceutical plants use hygienic tube for product pipework, in 316L with a polished bore. Chemical and process plants use welded and seamless pipe for aggressive media, in 316L and duplex. Marine and coastal work uses 316L and duplex for its chloride resistance. Heat exchangers use thin-wall tube in the grade the process demands.

Handrail and balustrade tube

Round tube in 304 and 316 is the backbone of stainless balustrades and handrails, in a brushed or mirror finish. Common handrail sizes include 42.4 and 48.3 mm outside diameter, matched with smaller tube for the balusters and infill. For coastal and exterior balustrades 316 is specified for its chloride resistance, since 304 can tea-stain near the sea. The tube pairs with stainless fittings, brackets and glass clamps to build a complete system, and ULAMEX supplies the tube in the grade and finish the design calls for.

Fabricating stainless tube

Stainless tube is bent on a mandrel bender to keep a round section through the bend. It welds with a matching low-carbon filler, and for hygienic pipework orbital TIG welding gives a clean, repeatable internal weld. As with all stainless, keep tube away from carbon steel tools to avoid iron contamination, and specify a low-carbon grade for welded fabrication. A welded joint is pickled or passivated afterwards to remove heat tint and restore corrosion resistance. For pressure pipework the wall is set by the schedule and the standard, and a 3.1 certificate to EN 10204 documents the material against the pressure rating and the traceability the job needs.

Weld cleaning and passivation

Welding stainless tube leaves a heat tint at the weld that reduces corrosion resistance if it is left in place. Pickling paste or electropolishing removes the tint and passivation restores the passive layer, which is essential on exterior and hygienic tube. For a finished handrail or pipe run, cleaning the welds back to bright metal is what preserves the corrosion resistance of the grade.

Stainless tube versus other tube

Stainless tube is chosen where corrosion resistance, hygiene or appearance justify its cost over galvanised or aluminium tube. Galvanised steel tube is cheaper for structural and fencing work where a zinc coating handles corrosion, but does not suit food, chemical or visible architectural use. Aluminium tube is lighter and needs no coating but is softer and less strong. Stainless wins for handrails, food and process pipework, chemical service and marine tube. ULAMEX supplies stainless alongside galvanised steel and aluminium tube, so a project sources the right material from one supplier.

Stainless steel tube from ULAMEX

ULAMEX has supplied stainless steel since 1988, and tube and pipe are a core part of the range.

Need stainless tube or pipe for a project? Send the grade, section, dimensions, standard and finish, and ULAMEX will return a non-binding quotation. Browse the stainless steel tube and pipe range, see our stainless steel sheet guide and supply capabilities, or contact the export desk at [email protected] or +48 504 424 761.

Frequently asked questions