If Scrap Trawler and another artifact you control are put into a graveyard at the same time, Scrap Trawler's ability triggers for each of them.

The target artifact card must have a lesser converted mana cost than the artifact that caused Scrap Trawler's ability to trigger by being put into a graveyard. Use the artifact's converted mana cost as it last existed on the battlefield to determine what may be returned.

While on the battlefield or in a graveyard, in an object's mana cost is 0.

If an artifact is a copy of another artifact with greater converted mana cost, such as Sculpting Steel copying an artifact with converted mana cost 4, Scrap Trawler's ability can target that artifact card in your graveyard when that artifact is put into your graveyard.