The heavier fractions of crude oil are either solid (bitumen and fuel oil) or thick viscous liquids (lube basestock and heavy gas oil). However, we have to move around the refinery through pipes and pumps. The only way to do this is to keep them hot.
Hot oil is less viscous than cold oil - i.e. it is more runny and flows more easily. When the fractions come out of the distillation column, they are already hot. However, they would soon cool down in normal pipes, clogging up pumps and the pipes themselves. So they have to be kept hot.
We do this using special pipes with steam tracers. The tracer is a pipe that runs alongside the oil pipe. It carries pressurised steam at up to 270°C. The assembly is then wrapped in thick insulation to reduce losses by conduction. This is covered in a shiny, metallic jacket that reduces the radiation (shiny surfaces radiated less than dull, black surfaces).