To minimize fouling, what fitting is used for bends to change direction of transfer line. Would a long radius 90 deg elbow have an advantage over a tee? Would two 45 deg be preferred over a 90? Ease of cleaning should also be considered. Is there a best practice for this, and is so what is it?
It depends on factors such as material availability, plant preference and access location.
Crosses with two blind flanges allow cleaning in two directions, while a tee (with 1 blind flange) will allow cleaning in only one direction. Flanged 90 degree elbows allow cleaning in two directions, but are more difficult to unblolt from the piping compared to a blind flange. (depending on the piping layout, you might require temporary supports).
Coke will build up inside of the pipe. I have seen 1-1/2 inch buildup inside the transfer line.
In our transfer line, the coke buildup is thicker in the area just before and just after the 90 degree turns. Our thinking was that perhaps the 90 creates back mixing that could increase coke formation in these areas. Your thoughts?