HELIOS 2 FISHSCALE is an equipment capable of preventing the risk of fishscaling by testing the steel before vitreous enameling.

HELIOS 2 FISHSCALE is an innovative laboratory instrument capable of conducting electrochemical tests to measure permeation through steel.

Pc with dedicated HELIOS App

Electrochemical cell and measuring probe

Liquid pumps for automatic solution recirculation


LETOMEC launched HELIOS 2 FISHSCALE on the market in 2015 during the 23rd INTERNATIONAL ENAMELLERS CONGRESS. Thanks to HELIOS 2 FISHSCALE, LETOMEC and ELECTROLUX received the Innovation SMAU Award in 2016. Moreover, the main european steel manufacturers validated the measurement principle.

HELIOS 2 FISHSCALE is capable of conducting tests in accordance with the UNI Standard 11734:2018. Now it can also perform tests in accordance with the European Standard EN 10209 Standard.

The HELIOS Platform including HELIOS 2 FISHSCALE is covered by the Patent N. EP 2912452 B1.


Home appliance industry

Steel industry

Porcelain enamel R&D laboratories


Fishscale defect is mainly caused by an excess of hydrogen absorption in the steel during enamel firing, caused by the dissociation of water vapor at high temperatures.
In the subsequent cooling stage, the hydrogen atoms tend to slowly migrate towards the enamel-steel interface. In this region, hydrogen atoms concentrate as the vitreous layer is not permeable to hydrogen, thus reaching high pressure. As a consequence, small chips of enamel may detach from the layer even later in the product manufacturing process, making the part non-compliant.

The susceptibility of steel to fishscale formation depends primarily on its quality, especially the content, distribution, and nature of hydrogen-trapping sites. These sites play a crucial role in preventing hydrogen diffusion towards the surface. The hydrogen diffusion coefficient, which is determined through an electrochemical permeation test, is inversely proportional to a steel’s trapping capacity. In simple terms, the higher the hydrogen diffusion coefficient, the greater the likelihood of fish-scale formation.


  • Easy calibration using pure iron specimens

  • Robust equipment for industrial use

  • Quick measures

  • Test result on steel is not affected by the enamel or firing condition

  • Safe analysis with non hazardous chemicals

  • User-friendly interface

  • Data can be stored and are remotely accessible


By following predefined hydrogen charging conditions and utilizing a pre-calibrated sensor, it is possible to perform electrochemical permeation tests to determine the apparent diffusion coefficient through steel. The hydrogen apparent diffusion coefficient provides insight into the probability of fish-scale formation on enameled products.

During the test, the steel sample is directly exposed on one side to the solution contained in the electrochemical cell and on the other to the probe. A defined current is set between the steel sample (cathode) and the anode. Hydrogen atoms are consequently produced inside the cell, on the steel surface. Afterwards they are adsorbed and can diffuse through the metal thickness, until they desorb from the other surface. The probe, containing a hydrogen gas sensor, is located on the exit sample surface in order to measure the flux of permeating..At the end of the test, the hydrogen flux is processed by proper mathematical codes to assess the hydrogen diffusivity in the steel and, consequently, the suitability of the steel for the enameling process.

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We are available to demonstrate HELIOS 2 FISHSCALE capabilities through free tests on your samples!

LETOMEC has a high-specialized laboratory dedicated to the study of hydrogen effect on materials’ behaviour.
Testing capabilities are ever-expanding to support companies in approaching the global energy transition. Tests in gaseous hydrogen environment and hydrogen mixtures are included in the service catalogue.

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