The pipe is not welded to heater shell like in ordinary equipment. Heater have a hole, the pipe runs through that hole inside the heater body.
There are two modeling techniques:
- First method. Use an anchor at the point where the piping goes inside the heater. The heater vendor must provide the allowable loads for this anchor point. Or API 560 code may be used
- Second Method. Model whole or part of the furnace coil that is inside the heater. Vendor should provide allowable displacements at the point where the pipe goes inside the heater (+dx, -dx, +dy, -dy, +dz, -dz). Usually it’s the gap values between the pipe and heater shell
You can choose one of these two methods.
First Method – Allowable Loads
First method is very conservative. The loads on heater usually are very huge, but allowable loads are very small and can’t be met.
Second Method – Allowable Displacements
Using the second method it is more easy to satisfy the vendor requirements. There’s no need to model whole furnace coil, just 3-4 U-Tubes is enough.
The supports in the furnace coil should be modeled correctly.
The following conditions should be met:
- Pipe displacements at the point where pipe hoes inside the heater should be less than vendor’s allowables
- All stresses both in the pipe and in the furnace coil should be less than allowable according to the selected code
- Loads on the furnace coil supports should be less than allowables