Because slacklining is still a young sport and there are still few materials and standards that are geared to the slackline application, material from other applications (from sports and industrial climbing to industrial applications) is used.
Here in this article it is shown that this is carabiners can be used in a few applications while slacklining. Be aware that you never use aluminum carabiners in your rig. They tend to break under cyclid load. 

 

This video shows how the carabiner shape affects the breaking load of triangular loads. 

The Test

In this test we compared Oval shaped carabiners (25kN) versus Pear shaped carabiners (50kN). The Pear shaped carabiners should be twice as strong. 
In the first test this could be confirmed, both carabiners held around 5kN more then they were rated. In a triload configuaration (anlge of 45º) the follow results were measured: 

  • Oval shaped: 29.9kN → was almost not effected by the triload
  • Pear shaped: 30.5kN (big bow is on the tri-loaded side → more force on the gate)

We then increased the angle of the triload to 55º:

  • Oval shaped: 29.8kN 
  • Pear shaped: 23.3kN (big bow is on the tri-loaded side)

We were curious what happend if we would turn the carabiner, so the triloading would occur on the smaller side; this affected the breaking strength a lot; 45kN

So if an situation occurs that you have to use a carabiner in a triload situation let it be an Pear Shaped biner on the small part or an oval carabiner (same BS, as straight load). THIS DOES NOT MEAN YOU SHOULD THIS REGULARY. This means it's always better to use an strong shackle in a triload situation. Whaterever your choice is, back-up your slackline. Be aware that during slacklining where high peak forces can occur the weaker biners are affected a lot.