Finishes
Surface Finishes:
Depending on the application, three finishes are available:
Finish A: No special requirements.
Finish B: Refined surface.
Finish C: Refined surface, free of defects.
Protection:
Galvanized steel sheets are generally delivered chromated and/or oiled, and prepared to prevent the risk of white stains.
Workability of Steel Sheets:
The workability of galvanized steel sheets is similar to that of cold-rolled steel.
Structural Steel:
Products are defined based on their final use and compliance with associated requirements, focusing on both the forming process (bending or rolling) and the desired metallurgical characteristics.
Painting:
Chromated or oiled galvanized steel sheets can be painted after degreasing and appropriate surface treatment.
STAINLESS STEEL SHEETS
Stainless steels are iron-based alloys composed of chromium, carbon, and other elements, primarily nickel, molybdenum, manganese, silicon, titanium, among others, which provide them with a specific resistance to certain types of corrosion.
Naturally, the influence of various elements leads to different variations in the intrinsic characteristics of the different types. The EN 10088 standard defines stainless steels as ferritic alloys containing a minimum of 10.5% chromium.
Based on their crystalline structure, stainless steel can be classified as:
Martensitic
Ferritic
Austenitic
Austenoferritic
SCREWS
The screws used are concave-headed and covered with plastic, providing a larger support surface and ensuring better sealing. They do not require washers. They feature a serration that prevents rotation during tightening, firmly securing them to the sheet. This type of screw is currently only manufactured in galvanized steel.
When using galvanized steel sheets, the screws are made of the same material. Standard hexagonal head screws (M-12) and washers are also used when necessary, depending on the type of construction material (stainless steels 316, 304, special steels, etc.).
Depending on the quality of the stainless steel, A-2 or A-4 fasteners are used.
When standard hexagonal screws are used, washers are installed both inside and outside. Regardless of the type of screw, the heads are always installed inside the tank, while the nuts are placed on the outside.
"U" PROFILES AND ANCHORS
“U” PROFILES
The “U” profiles are cold-formed profiles made from standard sheet metal, with general dimensions of 60 x 60 x 60 mm, and thicknesses ranging from 2 to 4 mm. All profiles are curved to adapt to the exterior perimeter of the tank.
Upper Profiles:
These profiles are installed around the entire upper perimeter of the tank and on the outside.
The vertical flange is bolted to the upper ring of the tank, and if necessary, it also supports the roof structure.
The upper horizontal flange is used to secure the roof sheets and trims.
Intermediate Profiles:
Depending on the dimensions of the tank, intermediate “U” profiles are installed to increase resistance to external agents.
These profiles provide additional structural strength to the tank.
Lower Profiles:
Installed around the entire lower perimeter of the tank and on the outside.
The vertical flange is bolted to the lower ring of the tank.
The lower horizontal flange rests on the concrete base and is secured with anchors.
ANCHORS
Once the lower “U” profile is installed, the final leveling of the tank is performed, and it is secured with M-16 x 120 mm expansion anchors.
Each sheet has two fixation points: one at the joint between sheets and another in the center of the sheet.
These anchors ensure a secure and stable installation, preventing any displacement or deformation of the tank.
SEALED
SEALING OF SHEETS AND SCREWS: SIKA
The sealing of all sheets and screws is done using mastics specifically designed for this purpose. The most commonly used products are Sikaflex TS Plus, Sikaflex 11 FC, Sikaflex Pro 2 HP, and Sikaflex Pro 3 WF.
These are one-component polyurethane sealants with accelerated curing.
Sealants based on silicones or other products are also used, depending on the liquid to be contained and the working conditions or application.
The sealant industry is rapidly advancing, and new products with better performance are constantly being developed, which means that the sealants listed in this manual may be replaced by others of higher quality and guarantee.
SEALING BETWEEN SHEETS AND CONCRETE BASE: HYDROTITE
The sealing between the lower sheets and the concrete base is achieved using a special expansion joint that reacts with water.
We currently use a product called “Hydrotite,” a hydrophilic rubber joint specially designed for sealing the metal-to-concrete connection.
The joint is adhered using mastic along the entire lower perimeter of the tank, positioned 50 mm from the first base in the form of a ring and above the first row of screws.
Only adhesives approved by the manufacturer should be used.
The standard length of the Hydrotite joint is 10 meters.
When there are joints between Hydrotite bands, a minimum overlap of 40 mm is required between them.
Installation Considerations:
A minimum concrete thickness of 100 mm should be present above the Hydrotite joint.
When the tank is filled, water is introduced to activate the expansion and sealing of the joint.
Special care must be taken to ensure that the Hydrotite joints are not damaged, detached, or moistened before the second concrete slab is installed.
To avoid irregularities, it is necessary for the Hydrotite joint to come into contact with the concrete within 3 days after its installation.
MEMBRANES
MEMBRANES
Membranes are used in tanks intended to contain highly aggressive liquids and sometimes in fire protection installations.
The membrane has the shape of a large bag that is installed inside the tank, and its installation is done simultaneously with the tank itself, with pistons positioned on the outside.
Tanks with membranes do not require mastic sealing, as the membrane itself ensures watertightness.
In cases where the liquid is extremely aggressive, selective sealing is applied, leaving weak points at the intersections of four sheets. These points act as an indicator in case of membrane rupture, preventing irreversible internal corrosion by providing early detection and avoiding stains across the entire tank exterior, localizing them only along these points.
Concrete Base:
The concrete base is similar to that used in mastic-sealed tanks in the initial phase.
Special attention must be given to the surface finish of the concrete, which must be finely troweled and polished to avoid tears and friction.
The second phase of interior concreting is not necessary; only the external perimeter ring is concreted.
Technical Characteristics of Standard Butyl Membrane
Physical Properties:
| Property | Unit | Requirement | Test Method |
|---|---|---|---|
| Hardness | °IRH | 65 ± 5 | BS 903 A26 |
| Modulus of Elasticity (300%) | MPa | min. 4.5 | BS 903 A2 |
| Tensile Strength | MPa | min. 8.5 | BS 903 A2 |
ROOFS
Currently, we manufacture two types of roofs for our tanks:
1. Conical Roof:
This type of roof is commonly used for industrial applications, wastewater, drinking water, and other liquids that may release vapors and fumes, as it is manufactured in all types of materials, and in stainless steel, it is highly resistant to such attacks.
This type of roof is manufactured with finishes in stainless steel sheets, galvanized steel, and epoxy-coated galvanized steel.
The support structure consists of double “U” beams, custom-made from the chosen material, arranged radially around the tank’s axis, forming a cone.
The beams rest on one end on a central pillar and on the other end on the tank’s perimeter “U” profile.
The central pillar is made of standardized tubing in the chosen material and has a variable diameter cone at the top, where the beam ends are bolted.
It also features radial reinforcements attached to each beam.
The closure sheets rest between the lower flanges of the “T” profiles and are bolted using M-12 standardized bolts with washers and nuts.
The sheets are overlapped from top to bottom and sealed with Sikaflex mastic.
The slope of the sheets, between 8° and 15°, prevents water accumulation.
2. Flat Roof:
This type of roof is normally used in tanks for fire prevention, irrigation tanks, and in all applications where there are no vapors or fumes produced by the stored liquids that could damage the galvanized coating.
This type of roof is only manufactured with a finish in hot-dip galvanized, corrugated steel sheets, reinforced by their folds.
The support structure is made of hot-dip galvanized steel Z-purlins and beams, arranged parallel to the tank’s axes, forming a support grid for the sheets.
The Z-purlins are hot-dip galvanized, with a variable height between 150 and 220 mm and a width of 50 mm on the upper and lower faces.
They are installed at variable distances according to the tank’s dimensions and the calculated load, typically ranging from 1,000 to 2,000 mm.
The ends rest on special supports attached to the perimeter “U” profiles.
For tanks with a diameter greater than 10,020 mm, additional beams and support pillars are required.
The beams are made of standardized tubular carbon steel profiles, arc-welded in a catenary shape, with supports designed to receive the Z-purlins, which are bolted in place.
The pillars are made of carbon steel tubes with a diameter of 100 mm or 150 mm and are equipped with upper mounting plates for the beams and lower plates for the concrete base.
The corrugated galvanized steel sheets are placed on the purlins, overlapped, and fastened with self-tapping screws with rubber washers.
They are installed in a way that the roof has a slope for water drainage towards the perimeter.
The edges of the sheets that extend beyond the tank’s perimeter are trimmed to match its shape and finished with a galvanized steel trim, fastened with self-tapping screws with rubber washers.
