Two abbreviations do most of the work on a Gulf materials submittal: GI and MI. They are not competing products. GI describes the finish — galvanised iron, meaning the fitting has been hot-dip galvanised after casting. MI describes the metal underneath — malleable iron. A galvanised malleable iron elbow is both at once, which is why the same item appears on one drawing as a GI elbow and on the next as an MI elbow, and why two suppliers can quote what looks like different material and mean exactly the same fitting.
This is a guide to what those fittings are, how they are sized, which thread to order, and what to look at when the pallet arrives on site. It is written for the UAE and the wider Gulf, where the buying pattern — ex-stock in Dubai or a container direct from the mill — changes the answer to some of these questions.
What the metal is, and what it buys you
Malleable cast iron starts life as white cast iron and is then annealed for a long soak at high temperature. The heat treatment breaks the brittle iron carbide down into nodules of graphite scattered through a ferritic matrix. The result behaves nothing like the grey cast iron it came from: it bends before it breaks, tolerates the shock of a wrench and a badly supported riser, and can be cut with a thread without splitting.
TUPY's threaded fittings are blackheart malleable cast iron in grade JMB 350-10, made to ISO 5922, ABNT NBR 6590 and EN 1562. The two numbers in the grade are the specification in miniature: a minimum tensile strength of 350 MPa and a minimum elongation of 10 per cent. That elongation figure is the whole argument for malleable iron in a threaded system. A material that stretches before it fails gives warning, and it survives the moment a fitter over-tightens a union late in the day.
A fuller explanation of the metallurgy is here, including how malleable iron differs from ductile iron and from steel.
The standards a threaded fitting is made to
Two different families of standard apply to any fitting, and confusing them is a common source of argument on submittals.
The material standards — ISO 5922, ABNT NBR 6590, EN 1562 — govern the iron itself: composition, microstructure, tensile strength, elongation.
The fitting standards — ABNT NBR 6943, ISO 49 and EN 10242 — govern the part: its shape, wall thickness, thread form, centre-to-end dimensions and the pressure it must hold. When a specification says “malleable iron fittings to EN 10242”, it is the second family being called up.
TUPY fittings are rated to a maximum working pressure of 25 bar up to 120 °C, with the derating above that set out on the standards page, alongside test pressures and the coating specification.
Sizes: what 1/4in to 6in actually covers
The threaded range runs from 1/4in to 6in. That single sentence hides a lot: across the range there are dozens of figures — elbows, tees, sockets, unions, bushes, nipples, plugs, caps, crosses, and the reducing versions of most of them — and several hundred individual size combinations once every reducing tee and eccentric bush is counted.
Rather than reproduce a table that goes stale, the dimensions page publishes every figure and every size with its centre-to-end dimensions in millimetres and its weight in both galvanised and black, generated from the catalogue itself. If you are building a BOQ, that is the page to work from.
One sizing point causes more ordering errors than any other. A fitting's size is its nominal bore — the approximate inside diameter of the pipe it takes — not the outside diameter of anything you can put a tape across. A 1in fitting does not measure one inch anywhere. Measure the outside diameter of the male thread and you will get roughly 33 mm on a 1in fitting; that is the thread's major diameter, and it is what a caliper reads. The thread guide sets out how to work back from a caliper reading to a nominal size.
BSP or NPT: the error that costs a delivery
Both threads exist in the Gulf and they do not mate. Ordering one against a drawing written for the other is the commonest mistake we see, and it is usually discovered only when the fittings are already on site.
| BSP | NPT | |
|---|---|---|
| Standards | EN 10242, ISO 49; threads to ISO 7-1 (taper) and ISO 228-1 (parallel) | ANSI B16.3, in Class 150 and Class 300 |
| Thread angle | 55° | 60° |
| Typical Gulf use | Building services, water, most fire protection | Oil, gas and industrial work specified by American engineering contractors |
A 55° and a 60° thread will start together and feel as though they are engaging. They will not seal. If a drawing is silent, ask before ordering.
Whole projects are sometimes written to one standard while a single package inside them — a compressor skid, a metering set — arrives specified to the other. It is worth checking package by package rather than once at tender.
Galvanised or black
Galvanised fittings are hot-dip galvanised after casting, so the zinc covers the thread as well as the body. Black fittings are supplied bare.
The service usually makes the choice for you. Anything carrying water, and anything exposed to Gulf air, is galvanised. Black is normal on steam, on condensate, and on lines that will be lagged and painted as part of a larger system. The comparison guide goes through where each belongs, including the cases where galvanising is actively the wrong answer.
What to check when the delivery arrives
Most of what goes wrong with a fittings delivery is visible in the first ten minutes, if someone looks. This is the check worth doing before the pallet is broken down and distributed around the site.
| Check | What good looks like |
|---|---|
| Cast markings | The maker's mark, the size and the pressure rating cast into the body — not stamped or printed on afterwards |
| Thread | Full, clean, unbruised threads; zinc in the thread on galvanised items, not bare metal |
| Galvanising | Even coverage, no bare patches at the seating faces, no heavy runs that will stop a thread engaging |
| Figure and size | Matched against the figure number on the order, not the description — descriptions vary between suppliers, figure numbers do not |
| Certificate | One that names the heat or batch, the grade and the standard, and can be traced back to what is in front of you |
| Listings, on fire work | The specific figures on the listing, since an approval covers named items rather than a whole catalogue |
That last row matters more than it looks. Approvals are granted figure by figure. “The brand is FM Approved” is not the same statement as “this elbow, in this size, is on the approval”, and the second is what a fire consultant will ask you to evidence. The figure-by-figure list is published here.
TUPY carries UL Listing and FM Approval on the relevant fire protection figures, DVGW approval on the gas figures, and ABNT and INMETRO certification in Brazil, produced under ISO 9001, ISO 14001 and ISO 45001.
Two routes into the UAE, and what drives the cost
There are two ways the same fitting reaches a Gulf site, and which is cheaper depends on the shape of the order rather than on the price per piece.
Ex-stock Dubai. The range is held here and cleared through Jebel Ali. This wins when the order is a spread of many figures in small quantities — the normal shape of a building services package — because it draws on a range that has already borne its freight.
Direct from Brazil. A full container shipped to your own port. This wins when the requirement is large and concentrated: one or two figures in volume, for a project that knows its quantities.
What actually moves the landed number is the mix of figures, the total volume, the port you clear through, and whether the goods are being re-exported or entering for local use. Price per piece is rarely where the difference is found. Both routes are quoted on every enquiry, so the comparison is made on one number rather than on a promise.
In short
- GI and MI describe the same fitting from two angles — the coating and the metal.
- Grade JMB 350-10 to ISO 5922, NBR 6590 and EN 1562; the fittings themselves to NBR 6943, ISO 49 and EN 10242.
- Size is nominal bore, never a measurement taken across the fitting.
- Confirm BSP or NPT package by package, not once at tender.
- Check cast markings, threads, galvanising, figure numbers and certificates before the pallet is broken down.
- On fire work, evidence the specific figure on the listing, not the brand.
Send the figures, sizes and quantities and both routes will be costed. Every figure number, dimension and weight is published on this site.
