What makes stress corrosion cracking so dangerous?


Stress corrosion cracking is very dangerous. It runs inside the workpiece along the crystalline boundaries and is invisible from the outside. The breakage of the workpiece is usually unannounced. The decisive factor is the choice of materials. Read here what happens during stress corrosion cracking.

Requirements for the occurrence

Stress corrosion cracking occurs only when certain conditions are met:

  • The material must be sensitive to stress corrosion cracking, which is not the case with all materials
  • There must be a tensile stress on the workpiece, in some cases also sufficient residual stress in the material, if they are high enough
  • There must be a corrosion medium present

Sensitive materials

This includes all aluminum wrought alloys as well as all types of brass. In addition, certain stainless steels are affected, as well as many steels that have high acid resistance. Stress corrosion cracking can also occur under certain conditions in plastics.

corrosion medium

For the stress corrosion cracking a trigger is necessary. This trigger is different depending on the metal group. For steels, it is mainly chlorides that also apply to aluminum. For brass, however, the number of possible triggers is greater:

  • ammonia
  • amines
  • sulfur oxides
  • Nitrogen oxides
  • Nitrite and nitrate
  • mercury salts

In addition, there are some other triggers that can cause stress corrosion cracking in brass.

Investigation for damages

Preliminary investigations would be extremely important since the time to break of the component can not be predicted. The time span can be minutes, but also years. At present, however, there is no method of investigation that is suitable for a proof. Only cracks and fractures can be found inside the metal - but the event itself is not.

avoidance

In any case, the selection of a potentially hazardous steel or other material can be avoided. Tensile stresses can also be structurally reduced or even circumvented. On the other hand, the influence of a trigger can not always be sufficiently influenced. So you have to focus on eliminating the first two factors to avoid damage in any case.

Tips & Tricks

Already many serious accidents are due to the occurrence of unrecognized stress corrosion cracking. A prudent avoidance of all design-related tensile stresses in endangered steel grades is therefore advisable in any case.


Video Board: Mod-01 Lec-32 Stress corrosion cracking: mechanisms(dissolution controlled)