Stress Analysis of Jacketed Piping System using Caesar II

Jacketed piping requires special stress analysis. Jacketed piping is commonly used to convey very viscous process fluids in an inner pipe, heated by steam/hot water/hot oil or other heating medium between the jacket and core pipe. Fig 1 shows normal components of a jacketed piping. General Definitions of Jacketed Piping Components are mentioned below:

Components of a Jacketed Piping System
Fig. 1: Components of a Jacketed Piping System

Spacer/ Guide Plate/ Spider:

Spacers shall be provided for supporting core pipe from jacket pipe and to ensure uniform gap between core and jacket pipes. The detailed dimensions and design of spacer shall be as design guide of jacketed piping prepared by layout team. Stress engineer to follow spider spacing chart while analysis.

Partition Plate/End Plate:

Partition plate or end plate shall be placed where the flow of steam or heating medium is interrupted for full jacketed system or at the end of partially jacketed system. The detailed dimensions and designs shall be as design guide prepared by layout team for jacketed piping.

End Closure:

End closure shall be used to terminate jacket piping. There are two types of end closure: Cap Type and Plate Type.

Jump-over:

Length of a single jacket circuit is limited & supply of heating medium cannot be provided separately for each circuit. Jump-overs (Fig. 2) are used to connect two different jacket circuits in series for continuous supply of heating medium and draining system. Details of Jump-over sizes and design shall be as per guide prepared by layout team for jacketed piping.

Fig. 2: Figure showing typical jump overs in Jacketed Piping System
Fig. 2: Figure showing typical jump overs in Jacketed Piping System

Jacket Medium:

Heating medium can be gas or liquid.

Reinforcing Ring Plate:

In case jacket pipe is to be terminated on core pipe having thickness of SCH 10S and below, the core pipe shall be suitably reinforced with a reinforcement ring at weld joint.

Supporting Concept:

All supports shall be provided on jacket pipe.

CAESAR II MODELLING 

Modeling the Core Pipe: 

  • Do not give insulation thickness while modeling core pipe.
  • Temperature should be the temperature of process line.
  • Pressure should be the pressure of the process line.
  • Fluid density should be the fluid density of the process fluid.
  • No wind/wave or earthquake to be applied on core.
  • All core bends are of large diameter (R = 1.5D). For slurry lines where radius may be 4D then same shall be entered (refer project standard).
  • In case of Cross-Arrangement for providing rodding facility, SIF can be obtained from vendor and shall be entered in all four points of Cross-Connection.
  • No supports shall come directly on core pipe.
  • Selection of node numbers is same as normal pipe modeling starting from node 10.
  • All spiders, which are acting as internal supports, can be modeled as vertical restraints plus lateral restraints (guides) with gap as mentioned in jacketed piping specification.
  • Location of spider shall be presumed before modeling & provide a free node at that location.
  • At places where jacket will be supported, give node numbers of those locations in core pipe like 5, 15, 115 (Refer Fig. 3) etc. All other nodes will be multiple of 10.
  • The starting and finishing node to rigid node should be defined as restraints, which will help to connect core pipe and jacket pipe.
  • All rigid elements shall be modeled as normal modeling procedure.

Modeling the Jacket Pipe: 

  • An easy way is to model the jacket pipe by running through the entire core and then duplicate the core piping using a proper node increment (like 1000).
  • Change the diameter of the jacket pipe according to the specifications.
  • Change the wall thickness of the jacket pipe.
  • All jacketed bends are of short radius i.e. R=1D. For slurry lines, radius may change. Refer project standard.
  • In case of Cross-Arrangement for providing rodding facility, SIF can be obtained from vendor and shall be entered in all four points of Cross-Connection.
  • Apply insulation thickness and insulation density.
  • Apply wind/wave/seismic if any.
  • Temperature should be the temperature of the heating medium.
  • Pressure should be the pressure of the heating medium.
  • All supports should be on jacketed portion only.
  • If steam is flowing in jacket pipe then put density as zero, otherwise follow the formula provided in the next point.
  • If both the jacket and the core are fluid filled, the fluid density of the jacket must be reduced to avoid excess (incorrect) weight. Caesar-II does not do this automatically.
  • Calculate the actual density as per below calculation:-
  • Actual jacket fluid density = [(rj2 – Rc2)/ rj2 ] x dj

Where,                  rj  = Inner radius of jacket;   Rc = Outer radius of core;       dj   =  Density of heating medium

Figure showing the node numbering
Fig. 3: Figure showing the node numbering

Combining the Core and Jacket Modeling:

  • The jacket will end with flange joints/ Plate/ Capped End. So at these points there will be physical connection between the core and the jacket. So these points need to be connected by anchor. For example if there is a flange at node 50 then;

50 ANC CNODE 1050; 60 ANC CNODE 1060

Delete the rigid element 1050-1060 from jacket portion.

  • At spider locations define Y, Z restraints (on the core pipe) if pipe is in X direction and then connect it by giving CNODE on jacket.
  • If the line is partially jacketed then model it same as the full jacket piping and delete the element from the jacket portion where the line is not jacketed.
  • Somewhere in full jacketed system delete the rigid element.
  • In some systems, the jacket and the core consist of different materials. This condition must be modeled very carefully, since the thermal growth in the core will be different from the thermal growth of the jacket.

ANALYSIS AND OTHER CALCULATIONS 

Click here to find the major checks which are required for jacketed piping stress analysis using Caesar II 

FEW POINTS TO TAKE SPECIAL ATTENTION 

  • In general engineering practice maximum length of jacket served by one hot water inlet shall be 20m and one steam inlet shall be 25m.
  • Same way the total length of one circuit shall not exceed 20m in case of continuous jacketing and 25m in case of discontinuous jacketing.
  • Max length required to a single jacket shall also dependent on buckling load (Pcr) check.
  • Jump-overs shall be designed such that air pockets may be avoided with heating medium as liquid.
  • Flow of heating medium through jacket shall be in series to avoid any cold point in system.
  • For heating medium as liquid the feed and drain nozzle shall be provided at the lowest and highest point of the jacket respectively. For heating medium as vapor the feed and drain nozzle shall be provided at the highest and lowest point of jacket respectively.
  • As far as possible flange joints on core pipe shall be avoided. They are to be provided only at equipment nozzles, valves, sp. fittings, instruments, etc. having flanged ends. Also for lines which need to be dismantled during maintenance.
  • Additional lateral restraints, in the form of spacers, can cause high axial loads which could conceivably initiate distress at the pipe to flange welds.
  • Spacers should be located to act only as ‘supports’ for deadweight bending of the core pipe. Indiscriminate location of spacers can produce a “locked-up” condition resulting in high expansion stresses. Check forces on Spiders. The forces shall not be too high that cause bending/ crushing of spiders. Spider is meant just for alignment.
  • Sometimes break up flanges may be required after each change in direction. Stress engineer to model the same from initial modeling. And sometimes in a straight run two-three break up flanges may come. In that case the force and moment at anchor points will be too high if temp differential between core and jacket is large.
  • Weight of flanges and valves used for jacketed piping and flanges will be reducing flanges and valves may be jacket valves. Weight shall be taken from vendor print.
  • After each jacketed reducer provide at least 300 mm spool piece (Refer Fig. 4) before attaching any flange or reducer to reduce chances of thermal failure, if required. Inform layout about this from initial stage to avoid unnecessary changes later. (For control valve assembly and psv lines)
  • Spool piece in between flange and reducer to avoid stress failure.
    Fig. 4: Spool piece in between flange and reducer to avoid stress failure.
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Anup Kumar Dey

I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

One thought on “Stress Analysis of Jacketed Piping System using Caesar II

  1. Sir I want to ask you a modelling approach for jacket pipe at termination point of connecting equipment.
    1.Can we anchor core or jacket pipe(Any one) and connect both by using C-Node?
    2.Mention two different anchors in both core and jacket and mention c node in any one of them?
    3.mention 2 different anchors of both core and jacket and one more anchor with c-node mentioned?

    Please clarify.

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