Cost estimates of a process plant’s piping show it makes up 25% of capital cost and 40% of detailed engineering cost. Facility layout can be designed to minimise piping length to reduce both these costs and operational cost of piping maintenance. However, mathematical formulations for layout optimisation typically minimise distances between equipment rather than actual pipe length connecting equipment, resulting in suboptimal layouts for pipe routing. To addresses this problem, a mixed integer programming formulation for layout optimisation will be developed that explicitly models pipe routes and pipe material. Layout optimisation is then subject to both equipment constraints (such as minimum separation distance) and piping constraints (such as allowable stress due to thermal expansion). Layouts will be produced where costs of unnecessary pipe loops and offsets are avoided through equipment placement and pipe material selection. The formulation developed by this project will be particularly useful for LNG plants, where pipe expansion loops are common and consideration of low thermal expansion materials during layout optimisation may lead to lower cost layouts.