Hello everyone,

Analyzing the system during blast scenario is a very difficult task and requires good judgement on the parameters to be used.

To make it more complex, we are currently looking into a piping system wherein the piping is insulated. The first thing that we've done is to consider the total area projected to compute for the drag load and gives a very conservative loads. This resulted to overdesigned supports.

My questions are:

1. Is it correct to consider the total area projected including the insulation to calculate the drag load?

2. What will be the allowable stress to be used - will it be the composite of insulation and the pipe or the strength of the pipe alone? - How to calculate the strength if it will came from the combination of pipe and insulation?

3. Will the insulation be deformed on a blast scenario? If yes, what will be the area to be used to calculate for the drag load?

4. Are the values given for CD and DAF from different sources consider the deformation of the area, on this case the total area including insulation?

Thank you in advance, and I hope you will find time to answer this post.

Regards,
jad

Answers ... my opinion only ....

1. Yes you use the total projected area. You might be able to apply a reducing shape factor (Cd), depending on the Reynolds number.

2. Ignore the small contribution to strength that the insulation may have. It is common to use yield stress as a sustained stress limit for blast.

3. Deformation depends on many factors ... like what the cladding is made of. Just ignore deformation.

4. Values of Cd are logically based on a cylinder. DAF is nothing to do with shape. I've never seen the shape of deformed cladding addressed.

Thanks for the answers MoverZ, I greatly appreciate that. We're trying to minimize the loads on the supports due to blast.

Follow-up question: is it more accurate to model the support in structural module of Caesar than to just specify restraints on specific node(s)?

Regards,
jad

If the flexibility of your support structure is significant, you should include it as a structural model. Usually this is not the case and simple modelling of restraints is enough.