Water Trap
A water trap commonly prevents smells, bacteria and insects entering the property. In refinery applications, it also prevents hydrocarbons and other gases from escaping outside through drains.
This particular water trap is used for a gas handling facility. It has baffle plate and grate strainer inside to collect debris and limit the ultimate size objects that will pass on into the rest of the piping, thereby catching over-sized objects. There is also an inspection port that serves as a cleanout feature.