Technical insight ·
Inside the BLUE-ARMOR Enamel Tank: Construction and Pressure Testing
The tank is the one part of a storage water heater that cannot be repaired, so its construction largely determines service life. Here is how OTTMEL builds and tests its BLUE-ARMOR enamel tanks.
Steel and coating
Tanks are made of Baosteel BTC340R enamel steel plate, chosen for its weldability, and coated with two layers of blue enamel. The coating is fired at 870–950 °C so that it has the same thermal expansion coefficient as the steel, which prevents cracking as the tank heats and cools.
Sandblasting before enameling
Before coating, the tank walls are blasted with steel shot to create a dense, uniform texture. After firing, the enamel locks into this surface profile, improving adhesion and durability.
Welding sequence
The tank has three parts: top head, shell and bottom head. All welds are made by automated gas-shielded welding. The top head is welded to the shell before enameling, and the bottom head is enameled before it is welded to the shell. This order keeps the welds sound and the enamel coverage continuous.
Pressure testing
| Test | Requirement |
|---|---|
| Hydrostatic test | Every tank is filled with water before assembly; no leakage is allowed at 1× working pressure |
| Overpressure test | No permanent deformation at 1.5× working pressure; no leakage at 2× working pressure |
| Pulse (cycle) test | Pressure alternated between 1× and 15% of working pressure for 250,000 cycles, with no serious deformation, leakage or damage to welds and fittings |
The pulse test simulates the pressure swings a tank experiences each time hot water taps are opened and closed.
Other protection features (electric models)
- High-density injected polyurethane insulation; OTTMEL literature states a temperature drop of less than 6 °C in 24 hours in cold winter conditions
- Two full-length anode rods inserted from the top of the tank to the bottom
- Units can be installed in parallel, so some can be switched off at low demand or for maintenance
