District cooling is the Gulf's answer to air conditioning at city scale, and the pipework that carries it splits into two jobs. The mains are welded steel or plastic; almost everything around them - branches, gauge and instrument connections, vents, drains, make-up water and the small-bore in every plant room and energy transfer station - is threaded, and that is where malleable iron (MI) fittings work.
A chilled water circuit is closed, treated with a corrosion inhibitor and largely free of fresh oxygen, so black malleable iron is the normal specification. Galvanising buys nothing in that environment, and zinc shedding into a treated closed loop is a nuisance the water treatment regime then has to deal with.
The exception is the make-up water line, which is usually potable and open to fresh oxygen every time it runs. That takes galvanised iron (GI). It is common for one plant room to need both finishes, which is worth getting right on the order rather than on site.
Chilled lines run below the dew point, and in a Gulf summer that means every uninsulated cold surface sweats. Straight pipe is easy to insulate; elbows, tees, unions and valve connections are where the vapour barrier gets cut, patched and eventually fails - and condensation running down the outside of a fitting corrodes it from the outside in, whatever the water inside is doing.
It is worth allowing for shaped covers over fittings and enough clearance to actually fit them. A tee crammed against a wall cannot be insulated properly, and the leak that appears two summers later is not a leak at all - it is condensate.
A tall building puts static head on top of pump pressure, and the fittings at the bottom of a riser see far more than the ones on the top floor. Class 150 is right for most chilled water work, but on high-rise risers and on the primary side of a large scheme the rating at the lowest point is worth calculating rather than assuming.
Chilled water is also cold, which is the friendly direction for malleable iron - the derating that matters on steam lines does not apply here, so the published cold rating stands.
Energy transfer stations: gauge and thermometer pockets, strainer and valve connections, drain and vent lines, small-bore bypasses. Plant rooms: pump gauge lines, expansion and make-up connections, chemical dosing tie-ins. Risers and floors: branch connections to fan coil units and air handling units, automatic air vents at every high point, drains at every low one.
Unions matter more here than on most services. Strainers are cleaned, control valves and sensors come out, and a joint that has to be broken for maintenance should be a union by design rather than a threaded joint someone has to cut.
| Material | Blackheart malleable cast iron JMB 350-10 (ISO 5922, EN 1562, ABNT NBR 6590) |
|---|---|
| Standards | EN 10242, ISO 49, ABNT NBR 6943 |
| Sizes | 1/4 inch to 6 inch |
| Maximum working pressure | 25 bar from -20 to +120 °C |
| Hydrostatic test pressure | 100 bar (1/8 to 4 in), 64 bar (5 to 6 in) |
| Threads | Internal parallel Rp, external taper R, to ISO 7-1 |
| Finish | Hot-dip galvanised to ISO 1461 and ABNT NBR 6323, or black (oiled) |
Black on the closed treated circuit - galvanising buys nothing there and the zinc becomes a water treatment problem. Galvanised on the potable make-up line. One plant room commonly needs both.
Class 150 covers most chilled water work, but static head at the bottom of a tall riser adds to pump pressure. Calculate the pressure at the lowest point; where it is high, Class 300 is the answer.
The fittings range covers 1/4in to 6in in BSP, galvanised and black, from stock in Dubai. Send the schedule and it is quoted as one order.
Condensation. Below the dew point every cold surface sweats, and fittings are where the vapour barrier is hardest to keep sealed. Allow for shaped covers and clearance to install them.
Stocked in Dubai and shipped across the Gulf, Iraq, Turkey, the Caucasus and South Asia.
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