By using jackets around a lined piping system, it is possible to provide a source of heating or cooling. The core pipe is completely surrounded by a jacket pipe and the process material travels through the lined pipe as normal, whilst the heating or cooling medium travels through the outer jacket.
How jacketed piping works
Jackets typically contain steam, hot water or oil which can be operated at temperatures equivalent to the maximum operating temperature of the lining up to 392°F or the required process temperature if lower. As long as the steelwork material is specified appropriately, jackets can also work successfully at cryogenic temperatures.
The jacket usually extends almost to the end of the pipe on a straight pipe spool, leaving some room to introduce the necessary vent between on the pipe. If the line is to be subsequently insulated such vents require welded bosses and extensions to ensure they system vents externally from the lagging.
Connections to the jacket can be flanged, threaded or according to the customer’s specifications.
Valves and fittings can also be jacketed, but it may be that their short length allows the process to remain heated, simply by insulating them.
The benefits of jacketed piping
The advantages of jacketing are that it allows for a smooth ramp up of temperatures – a useful attribute given the poor heat conducting characteristics of PTFE and PFA. Also, heat can be applied evenly to the pipe without the danger of localized hotspots, which can lead to localized liner damage or liner expansion, both of which can lead to liner collapse.