How to model a Jacketed Piping in START-PROF

Read about START-PROF pipe stress analysis software

Example project file: JacketedPipe.ctp

Jacketed piping requires special stress analysis.

Jacketed piping is commonly used:

• when the process fluid (usually very viscous liquid) needs constant and uniform heating, which can not be provided by satellite piping or electrical heating cable. Heating is usually carried out with a saturated steam, hot water or hot oil.
• when using the vacuum as an insulating layer. The most frequent use - for transportation of cryogenic liquids (e.g., liquid nitrogen)

The classic design solution is shown in figure below. Jacketed piping is a double-walled pipe. The special devices are used to control the distance between two pipes - spacers, guide plates, partition/end plate and spiders. Spacers support the core pipe from jacket pipe and to ensure uniform gap between core and jacket pipes. Partition plate and end plate placed where the flow of steam is interrupted.

Typical design scheme for warming viscous liquids

1 – inner pipe (core), 2 – outer pipe (jacket), 3 – flange pair, 4 - bypass pipe

Jacketed piping can be modeled as parallel inner and outer pipes connected with special elements -jumpers. The axial lines of these 2 pipelines are parallel with a small eccentricity 1-2 mm.

Jacketed piping model

1- outer pipe (jacket), 2 – inner pipe (core), 3 – jumper, 4 – fixed anchor

Outer pipe (jacket)

All supports are placed on the outer piping. The outer piping product weight should be reduced by the volume of inner pipe. Pressure in outer piping should be real. The insulation weight should be added only for outer pipe. The wind loads should be applied only on outer pipe.

Inner pipe (core)

The pressure in inner piping should be specified as difference between outer and inner pipe real pressure. Insulation weight should be zero, the product weight should be real. Inner pipe is supported by spiders that could be modeled in START-PROF as special jumpers.

Jacketed piping design

a – flange pair; b – support between core and jacked (spider); c - spider design.

1- outer pipe (jacket), 2 – inner pipe (core), 3 – flange pair, 4 – spiders

Jumper is a rigid element with an internal restraint in the middle, that allow the sliding between core and jacket along the pipe axis.

Two kinds of jumpers

a – jumper for spider modeling;  b – jumper for flange modeling;

1- outer pipe (jacket), 2 – inner pipe (core), 3 - custom expansion joint

Jumper properties:

• The length should be very short (for example 2 mm) to reduce the eccentricity influence

• Wall thickness should be equal to half of tie diameter

• Pressure should be zero

• Test pressure should be very small (1e-5 kgf/cm2)

• Operating temperature should be equal to Ambient temperature

• Weight should be very small (1e-5 kgf/cm)

• Insulation and fluid weight should be zero

• Length should be very small (2mm) to decrease the eccentricity influence of pipe axis

The flange pair jumper is modeled the same but without custom expansion joint.