Understanding modular bolted steel tanks

What it is, and why it is built rather than delivered

A moulded GRP tank is made in a factory in one piece and craned into position. That works until the tank is bigger than the crane, the gate, or the doorway. Above about 20,000 gallons, or anywhere inside an existing building, it stops working entirely.

A modular bolted tank solves that by arriving in pieces. The shell is made of curved, galvanized steel panels, each one a manageable size, bolted to its neighbours through flanges with a rubber gasket sealing the joint. A tank is described by how many rings of panels it has — the courses — and how many panels are in each ring.

It is a complete steel vessel: a steel base, steel walls and a steel roof. The water is held by the steel itself, sealed at every joint with a rubber gasket. There is no plastic membrane and no PVC liner anywhere in it.

So a tank listed as eight courses of twelve panels is ninety-six panels bolted into a cylinder on site. Every one of them was carried in by hand or on a pallet truck.

How the sizes work — diameter, height and courses

Capacity is set by two numbers: how wide the tank is and how tall. The standard range is built from courses 1,150 mm high, stacked between one and five high, on diameters from 1,894 mm to 11,364 mm. That gives 3.24 m³ at the smallest and 582.87 m³ at the largest, with ninety-three sizes in between.

The same volume can usually be reached more than one way. A short wide tank and a tall narrow one holding the same water are different products in practice: the wide one needs floor area and the tall one needs headroom and a stronger base. Tell us the space and we will pick the shape to suit it.

And the ninety-three standard sizes are a starting point, not a catalogue you have to choose from. The manufacturer builds to order, so a capacity that falls between two of them — or well beyond the largest — is engineered rather than rounded to the nearest listed size.

The steel, and why the bottom is thicker than the top

The shell is structural steel, grade S235JR, with stainless steel available where the stored liquid demands it. The panels are not all the same thickness: water pushes hardest at the bottom, so the lower courses are rolled from heavier plate than the upper ones. On a tall tank that difference is most of the cost.

It is also why a tall tank costs more per cubic metre than a short one of the same volume. You are not paying for more water, you are paying for the steel that holds the pressure at the base.

• Additional protective coatings and thermoplastic linings where the liquid or the environment requires them.
• Potable water coating to WRAS / BS 6920 is offered as an option — ask for the approval reference before specifying it for drinking water.
• There is no single wall thickness to quote for these tanks, and anyone who gives you one has not engineered it. It falls out of the diameter, the height, the water head and the design loads, and the manufacturer issues the thickness schedule with the technical submittal. The agricultural range is the exception: it is 1.5 mm throughout, because it is a wall ring rather than a pressure-retaining vessel.

How a bolted tank stays watertight

This is the question every engineer asks, and it is a fair one: a tank made of ninety-six separate pieces has a great many joints in it.

Every seam carries an EPDM rubber gasket, compressed between the panel flanges as the bolts are tightened. The bolts are high-tensile and galvanized like everything else, and they are torqued rather than simply done up. The seal is made by compression on the gasket, not by sealant smeared into a gap, which is why a properly built bolted tank does not weep and why the panels can be unbolted and the tank moved or extended later.

NBR gaskets replace EPDM where the stored liquid is petroleum-based or chemically aggressive.

Roof, ladder and the fittings that come with it

A tank is more than a shell. The standard scope on an engineered tank includes the roof and everything needed to use and maintain it.

• Self-supported conical roof — no internal columns standing in the water.
• Roof access manhole, and a handrail around the roof edge.
• External access ladder with a safety cage; stairs on the larger tanks.
• Inlet, outlet, drain and overflow connections, and a vent pipe.
• The complete bolting system, gaskets and anchor fasteners.

What has to be ready before the tank arrives

This is the part that catches people out, and it is worth being blunt about it. The tank is supplied; the ground it stands on is not.

A reinforced concrete foundation — a ring beam or a full slab, engineered to the tank's loaded weight and the ground conditions — must be cast, cured and level before anything is delivered. Civil works, excavation, the crane, the labour to build it, external pipework and any electrical work all sit outside the supply unless they are agreed in writing.

You are not left to work out what it has to carry. The manufacturer is an engineering company, and once the tank design is approved they issue the foundation loading and the foundation design requirements for it — the loads, the bearing arrangement and what the base has to do. Your civil contractor then designs and builds the reinforced concrete to those drawings and remains responsible for it. That split is the normal one on this kind of tank, and it means your engineer is working from real numbers rather than an assumption.

Who bolts it together

A flat-pack tank has to be built by somebody, and it is a real trade rather than a day’s labouring: the courses go up in sequence, every gasket has to seat, and every bolt is torqued to a figure. A joint that is under-torqued weeps and a joint that is over-torqued crushes the gasket, and both are found by the water rather than by eye.

There are two ways to have it done, and the right one depends on whether you already have a competent crew on site.

• Assembly runs about ten days for a large tank once the base is cured and level.
• The base being ready is the gate. A crew standing beside uncured concrete is billable time.

Standards, approvals, and what we will not claim

The tanks are engineered to internationally recognised standards. AWWA D103 is the reference for bolted, factory-coated steel water tanks, covering design, materials, coatings, fabrication and testing. NFPA 22 applies where the duty is fire water storage. API 12B covers bolted production tanks, EN 1993-4-2 is the Eurocode for steel tank structures, and EN ISO 28765 covers the bolted tank design itself. The manufacturer holds ISO 9001, ISO 14001 and ISO 45001 management system certificates.

Each tank is engineered for its own site: capacity, wind speed, seismic conditions, soil, snow load where relevant and foundation conditions all feed the structural design, and the design and technical documentation are produced for submission to the local authority.

The agricultural tank is a different animal

One product in this range is not a closed tank at all, and it is worth understanding separately because it is far cheaper per cubic metre than anything else here.

An agricultural or irrigation tank is an open-topped ring of galvanized corrugated steel. There is no roof and there is no steel floor. The ring is bolted together on site, and a PVC membrane liner is fitted inside it — effectively a balloon that holds the water while the steel ring takes the load and keeps its shape. Water never touches a steel seam, so the whole question of gaskets and torqued joints does not arise.

That makes it the cheapest way to hold a large volume outdoors: irrigation and fertigation, livestock water, rainwater harvesting, or bulk water on a construction site.

Forty standard sizes run from 14 m³ to 995 m³. The ring is built from 0.85 m courses, so it comes 2.55 m tall in three courses or 3.40 m in four, and the diameter sets the volume — from 2.68 m across at the smallest to 22.29 m at the largest.

Be clear about what you are buying. It is deliberately simple equipment: a wall ring and a liner, no floor, no roof, thinner sheet than the bolted tanks. That simplicity is the whole point — it is why a 995 m³ agricultural tank costs a fraction of a closed tank of similar volume — but it is equipment for a field, not for a building.

The liner is also the part that will need replacing first. The bolted tanks above hold water in steel and seal it with a rubber gasket, so there is no membrane to puncture or to perish in the sun. Here the membrane is the only thing between the water and the ground, and it is a consumable.

• Open at the top — not for potable water, and it will collect dust and debris.
• No steel base: it stands on level compacted ground or a concrete ring.
• The membrane is the water barrier and is replaceable.
• Access is by a ladder over the wall.

How long it takes, and what the order looks like

These are manufactured to order in Türkiye and shipped flat-pack. The sequence is fixed and worth understanding before you commit to a programme.

• Confirm the requirement and the site conditions.
• Technical and commercial offer, then a proforma invoice — which is where the warranty period is stated.
• Engineering finalised and manufacture starts.
• Packed for export as a flat-pack kit and shipped.
• Clearance, delivery, assembly and handover.

What the warranty is

Two to three years in general, and that is the manufacturer’s own wording rather than a number we have rounded up. The exact period, and exactly what is covered on the coating, is stated against the specific product and the specific offer — so it is on the quotation you sign, not on this page.

We would rather print the general figure and let the offer be precise than advertise a headline period the paperwork does not support. If a warranty length matters to your specification, ask for it in writing before you order and it will be confirmed for the range you are buying.

Why the price is quoted and not printed

The water tank and shipping container ranges on this site carry a real published price in AED. Not this one, and the reason is honest rather than evasive.

The cost of one of these depends on the wall thickness the height demands, the coating the stored liquid demands, which accessories are fitted, and the freight, insurance, duty and clearance to land it in the UAE. Two tanks of identical volume can differ substantially on all four. A printed figure would be a figure we could not stand behind, which is the one thing this catalogue exists to avoid.

Send the volume, the location, what is being stored and the space available. You will get a real number against your actual job.