Sugar mill quality brass tubes for juice heaters, evaporators and pans

It is a trade phrase, not a standard. When mill engineers and tube dealers in India use it, they almost always mean seamless tube in 70/30 brass with a small arsenic addition, drawn to the OD and gauge the mill's heat exchangers were designed for, with an annealed or stress-relieved temper that will take expansion without splitting.

Three things separate it from general brass tube. The chemistry includes arsenic, which protects against dezincification in hot juice and condensate. The OD tolerance is tight, because the tube must expand evenly into the tube plate hole and seal. And the temper is controlled, since tubes that are too hard crack at the expanded end, while tubes that are too soft deform during handling and rolling.

Some mill specifications call for admiralty brass (70/30 with about 1 percent tin, UNS C44300, BS CZ111), particularly on condensers. If your drawing names admiralty, send it to us and we will confirm what we can supply.

Juice heaters raise raw and clarified juice temperature using vapour bled from the evaporator. Tubes in these heaters typically run 38 to 50 mm OD and 3 to 6 metres long. The evaporator bodies, usually a set of four or five effects, carry the largest number of tubes in the calandria. Vacuum pans use shorter, wider tubes in their calandrias to boil massecuite. Brass is used throughout because it conducts heat well, resists the mildly acidic juice and can be expanded and re-expanded into tube plates during maintenance.

The usual culprit is ammonia. Cane juice releases small amounts of ammonia as it is heated, and it collects in the vapour and condensate on the steam side of later effects and juice heaters. Brass that carries residual stress, especially at the expanded ends near the tube plate, can then fail by stress corrosion cracking. The National Metallurgical Laboratory has published a case study tracing cracked 70/30 evaporator tubes to exactly this mechanism.

The practical defences are stress-relieved tubes, correct expansion (over-rolling leaves high stress at the tube plate), and good venting of non-condensable gases so ammonia does not concentrate. Erosion at tube inlets and dezincification in poorly treated water are the other common failure modes.

Many mills have moved some duties, especially juice heaters, to stainless steel tubes, and engineering texts on juice heater design commonly give brass or SS 304 as the two tube options. Stainless steel does not suffer ammonia cracking or dezincification and lasts longer, but it conducts heat far less well, so a heater needs more surface for the same duty. Brass is easier to expand and re-expand, and existing heaters designed around brass tube dimensions are simpler to retube in brass.

If you are weighing the change, our stainless steel pipes and tubes page covers the SS side. For the brass itself, see the 70/30 brass grade page.

Tube orders for the off-season usually go wrong in the details: a gauge that does not match the existing tube plate holes, lengths that leave no allowance for expansion and trimming, or tubes that arrive too hard to roll. Use the checklist below and send it with your enquiry. More on what we supply to the industry is on our sugar mills and distilleries page.

Plan the order early. Sugar mill brass tubes are bought in large numbers for a short off-season window, and a delay in confirming sizes can push the job into the crushing season. Sending us the drawing or a sample tube a few weeks ahead gives time to check gauge, length and temper, arrange the test certificate and agree delivery to the mill before the retubing crew is on site.