In TT, a bolter or a space marine's close combat attacks (unarmed, combat knife, chainsword, power weapon, force weapon, frag grenade, whatever) has a 5/6 chance to do nothing, and a 1/6 chance per hit of inflicting a glancing hit. A krak grenade has a 1/2 chance to do nothing, 1/6 chance to glance, and a 1/3 chance to penetrate. A power fist has a 1/6 chance to do nothing, a 1/6 chance to glance, and a 2/3 chance to penetrate. A melta bomb has a 1/36 chance to glance, and a 35/36 chance to penetrate. A Space Marine has 1 Attack, +1 if he charges, +1 for two weapons. (Only only attack if it's a grenade.)
A glancing hit has the same effects as Righteous Fury in the RPG, but can wreck an immobilized, weaponless vehicle. A penetrating hit has a 2/3 chance of doing the same as a glancing, a 1/6 chance of wrecking it, a 1/6 chance of explodes.
Still calculating how that translates...