Shares in engineering firm UGL have tumbled after its joint venture partner flagged a $US170 million ($A200 million) cost blowout to the construction of a power station at Inpex's Ichthys LNG project in Darwin.

Shares in engineering firm UGL have tumbled after its joint venture partner flagged a $US170 million ($A200 million) cost blowout to the construction of a power station at Inpex's Ichthys LNG project in Darwin.