EE stated that he was assisting two other EE's to loosen a coupler between a 6"" and 4"" discharge line in the 1 Left Bleeder aircourse. A co-worker was using a ratchet to attempt to loosen a rusted bolt. While the EE was prying on the bolt, a rope broke that was holding the discharge line causing the injured EE's hand to be caught between the two coupler resulting in a bruise.