Instrument Leads in any type of service that could possibly poymerize or plug due to solids, need to be so designed that they can rodded out while in operation. This is a higly specialized design field requiring experience and expertise with instrumentation and the process medium. A good place to start is with the ISA.
One trick learned from experince is to utilise a teflon spray lube on components. At least when the styrene gels or polymerizes, it's easy to disassemble the instruments and components and clean off.