Code for Fire Protection Design of Petrochemical Enterprises 7.2.5
Thread Content
7.2.5 When process and utility pipes are laid side by side in multiple layers, pipes with a medium operating temperature of 250°C or higher should be placed on the upper layer, while pipes for liquefied hydrocarbons and corrosive media should be placed on the lower layer； Pipes that must be installed in the lower layer and for which the operating temperature of the medium is 250°C or higher can be placed on the outside, but they should not be adjacent to liquefied hydrocarbon pipes. The medium operating temperature for most bottom-of-tank pumps is equal to or higher than 250°C. When the bottom-of-tank pump is located beneath a pipe tray (bridge), in order to minimize the liquid level in the tower and meet the requirements regarding the effective net positive suction head of the pump, this specification stipulates that the pipes can be installed on the outer side of the lower layer of the pipe tray. I don’t understand how the explanation in the text relates the placement of pipes in the lower layer of the pipe tray to meeting the net positive suction head requirement of the pumps. If it is a pipe rack on the pump outlet pipeline, there is no impact between the upper and lower layers ； Conversely, if the pump’s inlet pipe is located in a ductwork system on an upper level, the head pressure is higher, so the effective net positive suction head should be greater, right?
To minimize the liquid level height in the tower, draw a diagram by yourself,...
Conversely, if the pump’s inlet pipe is located in a ductwork system on an upper level, the head pressure is higher, so the effective net positive suction head should be greater, right? Isn’t this statement incorrect? Reaching the upper level means a higher liquid level in the tower, making cavitation more likely.
I’m sorry, I don’t understand what you mean. The pipes on the upper and lower levels of the pipe tray aren’t necessarily related to the tower liquid level, right?
I think the focus of the explanation is not the lower layer, but the outer side of the lower layer. Because the pump is generally oriented with its head facing the sides of the pipe gallery, while the motor is directed toward the middle of the pipe gallery, with common access passages on both sides. That’s why he had you arrange the pipes on the outside of the lower layer. On the lower level, it is because the pipes coming out of that level can be turned downward directly, which is more convenient than on the upper level; moreover, this prevents the formation of liquid pockets. (If the outlet of the tower is at 6m, the first layer of pipe racks is at TOS.5m, and the second layer is at TOS.8m, then liquid pockets will form if the pipes are placed on the second layer.) On the outside, the external inlet pipes should take as few detours as possible; you can go straight down from the outside of the pipe rack, and then create an inverted frame underneath the side beams of the first layer of pipe rack. The exit should be placed as close to the columns as possible, as it is possible to weld vertical guide frames or U-shaped clamps to those columns. Then walk straight down to the ground. This is the simplest trend.