How does hydrogen-induced brittle fracture occur?
Influencing factors and avoidance measures
Prerequisites for hydrogen-induced brittle fractures are
- the presence of a hydrogen supply
- during the manufacturing process
- while using the screw at the construction site
- the material condition
- the mechanical loading of the screw
The risk of a hydrogen-induced brittle fracture is only present when all three parameters are critical.
Optimisation in the manufacturing process
(at the EJOT plant)
The risk of the hydrogen-induced brittle fracture is reduced or can be detected early, amongst other things, by the material selection, exact process parameters and production-accompanying tests. In the case of galvanically applied zinc layers, however, the risk potential of a hydrogen-induced brittle fracture can never be excluded 100 %, according to the state of technology (for example, DIN EN ISO 4042). In addition, there is usually no conclusion possible about the exact supply of hydrogen in operation.
In simple terms, the release of hydrogen is minimised in the finishing process during surface treatment. The heat treatment ensures optimum core and edge hardness as well as sufficient toughness of the material. In addition, the hydrogen loading is further reduced by hydrogen annealing. Before delivery, the screws are subjected to a load test to minimise the risk.
Optimisation of the processing at the construction site
An efficient measure to reduce the risk of hydrogen-induced damage is the use of sealing washers. EJOT offers versions with pre-assembled sealing washer for all self-drilling and self-tapping screws of the JA, JZ and JT families..
Increased safety during installation
Sealing washers reduce the mechanical load and limit pretension force or tensile stress of the screws. The visible compression of the sealing washer during fastening allows a controlled tightening of the self-drilling screw. Tearing off of the screw head or stripping of the screw thread during installation is effectively avoided.
Increased safety after installation
Surface protection layers of the profiled sheets, which are damaged by the fastening process, can be safely covered with the sealing washers. The vulcanised plastic is characterised by high weather and UV resistance. This way the screw connection point is protected from weather influences until completion of the construction work. Due to the enlarged contact surface of the sealing washer, the values of the pull-through capacity are also increased.