CAESAR II and Rigid Elements: What is the point?

Components that are part of a piping system, such as valves, flanges, and other elements, are much heavier (and stiffer) than the pipe that connects to them. How does CAESAR II handle this? By using rigid elements. Let’s take a look at what a rigid element really is and how it affects your piping stress analysis.

CAESAR II is a 3D beam element solver that computes the element stiffness matrices and load vectors and then solves for displacements, forces, moments, reactions, and stresses.   The resulting information is compared against allowable stresses from the codes of construction.  While code standard calculations evaluate the pressure-containing capability of all piping components in a piping system (usually through the specifications of listed components), the code standards do not attempt to evaluate mechanical load on non-pipe components (such as a gate valve).

Why not?  Well, where is a system going to fail first, on the pipe, a valve, or a flange?  Typically, it will be the pipe.  Additionally, the geometry of non-pipe components are too varied and complex, so accounting for non-homogenous surface area calculations to determine failure on a component that has a very low chance of failing compared to pipe is just a moot point.

Enter the rigid element

This parameter can be applied manually using the Rigid selection box on the classic piping input screen.

Click the selection box to turn it on and two important things occur:

The first is that you have a new parameter that the object carries, “Rigid Weight”.  You can assign any number you want to the “Rigid weight” as it pertains to the object you are modeling.  For example, if this element was simulating two flanges and a gate valve, you would sum those individual component weights and enter that value into this field.

The second thing that occurs is that your element is displayed differently in the modeling window.  By manually entering the rigid element, I have converted element

20-30 to a bright green color with some symbolic geometry so that I can quickly recognize this element during my analysis.  Rigid elements can look differently so don’t worry about that too much right now.

So now that we have one, how does this affect the analysis?

Well, the job of the rigid element is to transfer stresses across the element.  When CAESAR II computes the stiffness matrix during an analysis and solves for loads, the rigid will transfer the load from one side of the pipe to the other. This is a very useful property for modeling more complex types of analysis.  For example, let’s take a look at modeling a vessel attached to piping in a CAESAR II analysis.

 

Vessel Example

Here I have a vessel modeled as the large, vertical cylinder, and a nozzle attachment modeled as the two rigid elements connected to the horizontal piping run on the right.  You’ll notice there is a

(

thin, green element coming from the center of the vertical vessel extending to the flanged connection on the vessel side.

What is important to understand here is that rigid elements retain thermal expansion as a property even though their main purpose is to transfer loads during an analysis.  So what I have effectively done in this case is accounted for radial expansion of the vessel by connecting my rigid element to the centerline of the vessel and extending it to the vessel’s radius.

There is more going on here but start to think about how you can apply this tool as a means to get more precise results from your analysis.  Let’s recap and describe a few more properties about this tool:

• Rigid elements main function is to transfer stresses between nodes in a piping system.
• A rigid element can be weightless, or you can define it a specific weight.
• Thermal expansion can be modeled within a specific application.
• The inherent stiffness of the element for analysis is based on ten times the wall thickness of your piping system.
• CADWorx will automatically export all non-pipe sections as rigid elements with their weight that was assigned in the specification with the C2OUT command.
• Rigid elements will not “fail” during an analysis.

Thank you,

-George

 

 

 

 

 

 

PV Elite 2015 Training

ECE is holding a 2 day PV Elite training class at our Houston Training Facility on Jones Road.

PV Elite 2015 Training: Houston, March 17-18, 2015

PV Elite Training covers fundamental guidelines for pressure vessel design.  The course will be focused on Section VIII Division I, and will cover local wind and seismic codes; however other codes and standards will be referenced.   Best practices for pressure vessel design are based on industry provided experience, which will allow attendees to ground engineering principles to real world applications. This course is not lecture based.  Content is applied to each core aspect of PV Elite to facilitate hands on learning.  Attendees will learn not only how to use PV Elite effectively but also learn how to become better engineers.

Day 1

Core concepts

• User interface fundamentals.
• Understanding code requirements for Section VIII Division 1.
• Allowable stress requirements and application to pressure vessels.
• Limiting MDMT requirements for nozzles and shells.
• Limiting factors for design of vessel, MAWP, MAPNc.
• Situations for utilizing PV Elite or CodeCalc.
• Design vs. Analyze modes for pressure vessels.
• Designing for internal and external pressure.
• Evaluation of nozzle designs and fabrication options for the designer.
• Cones and Conical sections.
• Options for skirt, saddle, base ring and leg and support lug designs.
• Analysis of results in PV Elite.
• Interoperability between PV Elite and CADWorx.

Day 2

Horizontal Vessel Analysis

• Saddle design and Zick Analysis for horizontal vessels.
• Heat exchanger tube sheet calculations.
• Heat exchanger expansion joint calculations.
• TEMA heat exchangers as well as UHX design.
• Importing WRC loads from CAESAR II
• Flange design and analysis.
• Welded Flat heads.

Tall Tower Analysis

• Allowable stresses on tall towers.
• Tower internals and mass distribution.
• Wind and Seismic codes and load factors.
• Platforms and wind area calculations.
• Computing natural frequencies for wind and seismic codes.
• Computing baserings using the standard and the neutral axis shifted approach.
• Calculations for lifting lugs.

Design and Evaluation

• API 579 for flaw and local thin area assessment.
• WRC 107/297 for nozzles
• Code Case 2695 using Division 1 allowables with Division 2 codes.
• Generating required report output for code compliance.
• Conformity assessment and QA procedures.

Please call or contact us for details and pricing.

All

PV Elite 2015 Service Pack 1 has been released and can be found on the Intergraph Smart Support Website.

To access the Service Pack:

1. Logon to Intergraph’s Smart Support System at https://smartsupport.intergraph.com.
2. Select the View Downloads tab.
3. Select PV Elite.
4. Select Service Packs and Fixes.
5. Select the download icon or the file link of the Service Pack.

If you have trouble accessing the Service Packs, need further information or a log on for Smart Support, please contact ECE Design.

CAESAR II 2013 R1 Service Pack 4 (6.10.04)

The CAESAR II 2013 R1 Service Pack 4 is now available for download from Intergraph’s Customer Smart System System.

To access this Hot Fix:

1. Logon to Intergraph’s Customer Response System at https://smartsupport.intergraph.com.
2. Select the View Downloads tab.
3. Select CAESAR II.
4. Select Service Packs and Fixes.
5. Select Previous Service Packs and Hot Fixes.
6. Select the download icon or the file link of the Hot Fix.

CAESAR II releases CAESAR II 2013 R1 Service Pack 4 (6.10.04)