Drawn brass pipes, tubes and capillary

The words get swapped freely on S.P. Road, but there is a real difference on a drawing. Pipe is sized by nominal bore, the way steel pipe is, with a wall thickness tied to that bore. Tube is sized by its actual outside diameter and wall thickness, for example 12.7 mm OD × 0.9 mm wall, or 1/2 inch OD × 20 SWG.

Most brass sold in India for engineering use is really tube, even when the enquiry says pipe. If you are matching an existing part, measure the OD with a vernier and the wall at the cut end, and send both numbers. That avoids the most common mix-up we see.

Wall thickness on Indian tube enquiries is still very often given in SWG (Standard Wire Gauge). The higher the number, the thinner the wall. The table further down converts the gauges you are most likely to meet into millimetres. If your drawing gives metric wall thickness, use that; we will not round it to the nearest gauge without telling you.

70/30 brass is the tube to pick when the tube will be bent tightly, expanded into a tube plate, flared or used in water service, because it is the most ductile and the least prone to dezincification. Its arsenical form is the standard for condensers and the juice heaters in our sugar mill quality brass tubes range.

63/37 is the general engineering tube: lamp stems, furniture, handrails, instrument casings and pressure lines where the duty is mild. It costs less and bends well in the annealed temper.

60/40 tube is stronger but takes little cold work, so it suits straight runs, bushes and parts machined from thick-walled tube rather than tubes that will be bent or flared.

Capillary is simply very small-bore drawn tube, typically with an OD of a few millimetres and a bore well under 2 mm. In brass it is used for pressure gauge and instrument connections, thermostat and sensing lines, burner jets, model engineering and small fluid metering lines. Because the bore is so small, cleanliness and bore tolerance matter more than on ordinary tube, so tell us the bore you need as well as the OD.

For refrigeration circuits, copper capillary is the usual choice, and for corrosive or high-temperature service stainless steel capillary tubes are the better fit.

Annealed tube is soft: it bends by hand or on a simple bender, flares and expands easily, but dents if handled carelessly. Half-hard tube holds its shape better and still bends on a proper former. Hard-drawn tube is stiff and straight, which suits rails, stems and parts that are machined, but it will kink or crack if you try to bend it tight.

If the tube is going to be bent, ask for annealed or half hard, and use a bending spring or a mandrel bender to stop the wall flattening.

To estimate weight, use 0.0267 × (OD − wall) × wall, with both in millimetres, to get kilos per metre. A 25 mm OD tube with a 1.6 mm wall works out to about 1.0 kg per metre. Drawn tube is usually sold in straight lengths of a few metres, and capillary is often supplied in coils. When you ask us for brass pipe and tube in Bangalore, give running metres or pieces and we will convert to kilos for the quote.

• IS 407: brass tubes for general purposes, the Indian standard most 70/30 and 63/37 tube enquiries refer to
• IS 1545: solid drawn copper and copper alloy tubes for condensers and heat exchangers
• ASTM B135: seamless brass tube for general engineering, covering grades such as C26000, C27200 and C28000
• EN 12449: seamless round copper and copper alloy tubes for general purposes, which includes CuZn37
• BS 2871: the older British tube standard, still quoted on many Indian drawings