Why is it necessary to increase the test pressure in the shell side so that it reaches the test pressure in the tube side when the pressure in the tube side is higher?

What is the purpose of doing this? Is it to check the pipe end?

To prevent unexpected operating conditions, that is, to ensure the housing can still withstand the situation when the heat exchange tubes rupture

It is to check whether the strength of the pipe ends meets the requirements; since the test pressure on the tube side is high, it is not possible to detect leaks in the pipe ends during hydrostatic testing on that side. Therefore, the pressure on the shell side is increased to assess the strength of the pipe ends.

This post was last edited by HSLJHZ on 2016-3-29 at 14:33. It seems that this topic has been discussed many times in the forum; I’ll quote what’s been said there: GB151 specifies requirements for pressure testing of heat exchangers – for those whose tube-side design pressure is higher than the shell-side design pressure, the drawings must outline in detail the testing methods and pressures applicable to the joints between the heat exchange tubes and the tube sheet. The following methods are generally used for handling this situation: 1. When the pressures in the tube side and shell side are not significantly different, the test pressure on the shell side can be increased to match that of the tube side. However, in this case, the components on the shell side must be tested under the increased pressure to ensure they can withstand it. 2. Use a permeable medium for pressure testing of the shell side; when the pressure on the tube side is much higher than that on the shell side, or when it is not possible to increase the pressure used for testing the shell side, a highly permeable medium such as ammonia can be employed for this purpose, in order to check the connections between the heat exchange tubes and the tube sheet. 3. Change the design pressure of the tube sheet – sometimes it is possible to modify the tube sheet design to use a pressure difference approach, thereby addressing the issue of higher pressure on the tube side compared to the shell side. See relevant books and standards for details. Standards are generally written this way for a reason. Has anyone thought about why this requirement is put forward (why is the design pressure for the shell side lower than that for the tube side, and why are stress tests or leakage tests carried out using the test pressure on the shell side as the standard)? ) This is mainly to address the situation where, during use, if the heat exchange tubes are damaged due to abrasion or corrosion, fluid from the tube side may leak to the shell side. In cases where the shell side is part of a closed fluid circulation system, the pressure on that side will increase gradually or rapidly. If there is no safety valve installed on the shell side or if the safety valve fails, the strength of the shell and the pipe connections attached to it will be put under severe stress, and there even is a risk of the container bursting. To eliminate this risk, this provision is considered in advance. If the design pressure of the tube side exceeds the maximum allowable test pressure on the shell side, but it is necessary to take the above requirements into account, the main pressure-bearing components such as the shell and tube sheet must be redesigned, usually by increasing their thickness.

A common issue is that the first method is used more often

It’s usually a fixed-tube-sheet heat exchanger, right?

HSLJHZ explained it very clearly! :lol

It’s actually about considering safety. Just in case

Actually, it is for pressure testing the pipe ends. During shell-side pressure testing, it is possible to conveniently and visually check for leaks at the pipe ends. During the pressure testing of the tubes, it is difficult to detect leaks at the tube ends in a timely manner due to the obstruction posed by the tube bundle; especially for the middle rows, these leaks are hardly visible at all. When the test pressure on the shell side is lower than that on the tube side, a pass on the shell side does not indicate a pass on the tube side. However, when the test pressure on the shell side is ≥ the test pressure on the tube side, approval for the shell side can represent approval for the tube side. Finally, another reason is that damage to the heat exchange tubes can cause pressure from the tube side to leak into the shell side (in cases of widespread tube failure), for safety reasons.