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Instruments located on jacketed pipelines

Preeti Raskar5 min read

Process experts recommend jacketed or traced pipelines based on fluid properties and site weather conditions.

Here we briefly address the engineering guidelines for instruments located on jacketed pipelines. To understand the instrument connections on jacketed pipelines, one needs to understand jacketed piping systems: their P&ID representation and the required connections.

General introduction to jacketed piping systems

Jacketed pipelines are generally used in process piping systems where solidification of the process medium may occur, or where jacketing is used as an anti-frost measure as recommended by process experts.

Jacketed pipelines help to convey complex process fluids (i.e. very viscous or likely to solidify) in an inner pipe, heated by steam, hot water, hot oil or another heating medium between the jacket and the core pipe.

Vacuum jacketing is also used as an insulator for cryogenic fluids.

Generally, the outer jacket pipeline is one size higher than the inner core pipeline, up to a certain line size. However, the project-specific piping specifications for jacketed pipelines shall be referred to for the details.

There are two types of jacketed pipelines:

Continuous / fully jacketed

All straight lengths, flanges, fittings, valves and branch connections are fully jacketed. The jacket is generally shown by a box around the item in the P&ID. There may be a note in the P&ID referring to the jacketed item.

P&ID symbol of a fully jacketed line: the valve is drawn inside a box joining the jacket on both sides

Fig. 1P&ID symbol of a fully jacketed line: the valve is drawn inside a box joining the jacket on both sides

Typical P&ID representation of fully jacketed pipelines:

For clarity, one needs to understand fully jacketed and partially jacketed type pipelines with respect to the pipe material specifications.

Example 1: Fully jacketed line showing jacketed valves

P&ID extract: the valves are jacketed, shown by the box symbol, a note and the in/out connections, with the LP steam jacket inlet (SL) and LP condensate jacket outlet (CL) marked

Fig. 2P&ID extract: the valves are jacketed, shown by the box symbol, a note and the in/out connections, with the LP steam jacket inlet (SL) and LP condensate jacket outlet (CL) marked

Example 2: Fully jacketed line showing jacketed isolation valves

P&ID extract: jacketed isolation valves, shown by the box symbol, a note and the in/out connections

Fig. 3P&ID extract: jacketed isolation valves, shown by the box symbol, a note and the in/out connections

Discontinuous / partially jacketed

In the case of partially jacketed pipelines, only the straight lengths of pipe are jacketed. Flanges, tees, elbows, branch connections and welds are not jacketed.

P&ID symbol of a partially jacketed line: the jacket stops on either side of the valve, which is not jacketed

Fig. 4P&ID symbol of a partially jacketed line: the jacket stops on either side of the valve, which is not jacketed

Or sometimes there is less possibility of the fluid solidifying in the pipeline while it is flowing, but it may solidify in the nozzle. In such cases, the pipelines are not jacketed and the nozzles are jacketed. Or jacketing is only considered for the straight lengths and for the nozzles, based on process recommendations.

Various types of partially jacketed lines are shown in the P&IDs as below:

Example 3: Pipeline is jacketed but inline valves are not jacketed

P&ID extract: valves that are not jacketed, as there is no box, note or in/out jacket connection, next to a jacketed valve with box and in/out connections

Fig. 5P&ID extract: valves that are not jacketed, as there is no box, note or in/out jacket connection, next to a jacketed valve with box and in/out connections

Example 4: Pipeline is not jacketed but isolation valves are jacketed

P&ID extract: the valves are jacketed, shown by the box symbol, a note and the in/out connections, but the line is not jacketed

Fig. 6P&ID extract: the valves are jacketed, shown by the box symbol, a note and the in/out connections, but the line is not jacketed

Example 5: Pipeline is not jacketed (it is traced) but isolation valves are jacketed

P&ID extract: the valves are jacketed, shown by the box symbol, a note and the in/out connections, but the line is traced, not jacketed

Fig. 7P&ID extract: the valves are jacketed, shown by the box symbol, a note and the in/out connections, but the line is traced, not jacketed

Jacketing connections in both types

In the case of a fully jacketed pipeline, the outer jacket pipe is welded to the back of the (modified) end flange of each jacket section. The inner pipe is welded into the modified flange, as shown below:

Drawing of a fully jacketed pipe spool: inner and outer pipe, modified blind flange, steam inlet and condensate outlet nozzles

Fig. 8Drawing of a fully jacketed pipe spool: inner and outer pipe, modified blind flange, steam inlet and condensate outlet nozzles

In this case, valves are bought as jacketed valves, with flanged inlet and outlet connections for the jacketing medium. Jacketed valves have a standard bore (to match the core pipe) and oversized flanges (to match the jacket pipe flanges).

Typical fully jacketed pipe:

Cutaway of a fully jacketed pipe showing the process line, outer jacket, steam inlet, condensate outlet and connection flange

Fig. 9Cutaway of a fully jacketed pipe showing the process line, outer jacket, steam inlet, condensate outlet and connection flange

Typical jacketed valves:

Three jacketed valves: a gear-operated butterfly valve, an actuated ball valve and a gate valve, each with jacket connections

Fig. 10Three jacketed valves: a gear-operated butterfly valve, an actuated ball valve and a gate valve, each with jacket connections

General arrangement drawing of a jacketed butterfly valve, marking the valve bore to match the core pipe, the valve flange to match the jacket pipe flange, and the jacket inlet, outlet and vent connections

Fig. 11General arrangement drawing of a jacketed butterfly valve, marking the valve bore to match the core pipe, the valve flange to match the jacket pipe flange, and the jacket inlet, outlet and vent connections

Typical jacketed flowmeters:

Catalogue extract of a classical venturi with a steam jacketing system, which gives protective heating so that solidification or condensation of gases is prevented

Fig. 12Catalogue extract of a classical venturi with a steam jacketing system, which gives protective heating so that solidification or condensation of gases is prevented

Mass flow meter:

A mass flow meter with its U-shaped measuring tubes enclosed in a steam jacket

Fig. 13A mass flow meter with its U-shaped measuring tubes enclosed in a steam jacket

Drawing of a steam heat kit and insulating jacket for a mass flow meter, with the tube coil, stainless steel straps, inlet and outlet, 50 mm insulation and dimensions

Fig. 14Drawing of a steam heat kit and insulating jacket for a mass flow meter, with the tube coil, stainless steel straps, inlet and outlet, 50 mm insulation and dimensions

For discontinuous/partial jacketing, the end of the jacketing is welded to the inner pipe.

Typical partially jacketed pipe:

A partially jacketed pipe section: the jacket ends are welded to the inner pipe

Fig. 15A partially jacketed pipe section: the jacket ends are welded to the inner pipe

Engineering guidelines for instruments located on jacketed pipelines (full or partial)

Inline instruments

For inline instruments, the jacketing requirement shall be considered as per the guidelines below:

  • The jacketing requirement shall be considered as per the P&ID representation (i.e. the jacket symbol), notes etc. Queries, if any, shall be discussed with piping and process at the beginning of the project.
  • For clarity, understand the jacketing requirement with respect to the pipe material specifications.
  • Jacketed inline instruments shall have a standard bore (to match the core pipe) and oversized flanges (to match the jacket pipe flanges), with flanged inlet and outlet connections for the jacketing medium as per the project specifications.
  • For jacketed instruments, details such as the jacketing medium process data, material, jacketing inlet and outlet connections and the related project specifications shall be communicated to the instrument vendor.
  • A proven track record for the supply of jacketed instruments shall be obtained from the instrument vendor, in order to avoid post-order issues.

Offline instruments

For offline instruments, the jacketing requirement shall be taken care of as below:

  • The jacketing requirement shall be considered as per the P&ID representation, i.e. if the root/isolation valve (i.e. the nozzle mating connection) is jacketed, then the instrument-side mating connection shall be as per the jacketing connection guidelines mentioned in the piping specifications, i.e. generally one size higher than the inner core pipeline, up to a certain line size.
  • Refer to the project specifications. If the main line and nozzle are jacketed for offline instruments, then the related impulse piping/tubing may require tracing/jacketing, a special size etc. The requirement shall be taken care of accordingly while engineering.