Modeling a Refractory Line with Insulation

Hello all
I have a line that has refractory and outside insulation. I have searched this forum and the Caesar Guides but have found no solution to modeling this piping system. I understand that when modeling refractory pipe you can set the insulation to negative thickness, that of the refractory used, and set the density. However my problem lies in the fact that I need to input the insulation as well. If any one has some experience in modeling pipe of this nature I would greatly appreciate some direction.

Regards

We "double dipped" here, and used the same input fields for two different things - insulation and refractory. You can't incorporate both in the same model using these input fields. You can model one, the other must be accounted for using uniform loads.

If your pipe is a gas line (like steam, where the fluid density is negligable), then it makes no difference which one you model and which one you incorporate as a uniform load. However, if you have a fluid line, I would model the refractory and use the uniform load option to include the insulation. The reason for this is so that c2 can properly determine the fluid weight in the reduced inner volume of the pipe.

Since you're using a uniform load vector (say U1) to model system weight, make sure that every place you have "W" in your load cases, you also have "U1". Also note that you can't run dynamics with this model, since the uniform loads won't transfer as part of the system mass.

Thank you Richard. You have been extremely helpful.

Nice and to the point explaination..

Thanks a lot

Things have changed since that earlier posting back in 2007. In c2 Version 5.30 (2011), we modified the structure of the input and now there are separate fields for: insulation, refractory, and cladding.

Mr. Richard,

My problem is to calculate the thermal expansion of the piping / equipment in the axial and lateral direction with the inside refractory lining. Is this is option is available in Caesar-II.

Since Caesar-5.3 have the provision of inputting the refractory details such as thickness and material, will that include the thermal expansion coefficient also.

Please clarify...

No, the only thing c2 does with refractory is adjust the weight of the system. c2 does not consider the refractory in the stiffness of the model on in its expansion characteristics.

Can you please provide any reference to calculate the thermal expansion considering the refractory lining.

As Richard told, By inputting refractory density and thickness, only weight gets adjusted.

Based on refractory thermal properties and method of application, metal skin temperature is calculated and it should be received from vendor. Different refractory brands have different thermal conductivity etc.
This metal skin temperature is used for CAESAR input. Combined thermal expansion co-efficient is not calculated here.

Now, to take care the stiffness of refractory, combined modulus of elasticity (refractory & steel) is calculated and the same is used in CAESAR.

This is the basic input I know. One can add more into it, if any.

Does the refractory really not impact the flexibility significantly? I've been taking it into account and wonder if I'm making my life unnecessarily difficult.

Ask a room of engineers what "significant" is, and you'll likely get a room full of engineers' worth of answers.

My definition of "significant" is whether or not its inclusion results in a change that would render the design from acceptable to unacceptable or from unacceptable to acceptable.

If you've been running the analysis and finding that it holds no impact in light of rules of thumb you could instead be using with an acceptable degree of precision, then perhaps.