Common problems and solutions of shell and tube heat exchangers

Common problems and solutions of shell and tube heat exchangers

The shell-and-tube heat exchanger has also become a heat retarder, which is mainly used in petroleum, chemical and other industries for medium heat exchange, and is one of the indispensable key equipment in the entire process.

The shell-and-tube heat exchanger is mainly composed of three parts, namely the front-end structure, the shell, and the rear-end structure.

Among them, the tube bundle in the back-end structure is one of the most important components. It undertakes the performance of medium heat transfer and heat exchange, and the heat exchange tube determines the heat exchange area of the heat exchanger.

Reasons why shell and tube heat exchangers are prone to problems

1. There are too many pipe heads, and the welding work is heavy, which is prone to welding defects;

2. The working condition of the pipe head is extremely harsh;

3. The induced vibration generated by the shell-side fluid during the operation of the heat exchanger causes continuous vibration of the tube bundle, which is one of the main factors causing damage to the tube head.

4. Erosion or corrosion of the tube head by the tube-side medium.

Common Tube Head Manufacturing Questions

1. Quality problems of weld seam welding

Partial burn-through of the heat exchange tube at the tube head; undercutting or fusing of the tube wall of the tube head heat exchanger along the circumferential direction; undercutting at the root of the weld seam between the tube sheet and the heat exchange tube; The upper half circle in the direction is larger and the lower half circle is smaller; there are air holes in the weld seam of the tube sheet and heat exchange tube; the height of the weld foot is lower than the drawing requirements or the thickness of the weld seam is not enough.

2. The length and expansion of the extension of the heat exchange tube

The length of the heat exchange tube protruding from the tube sheet is too long or too short, which is different from the drawing design; the expansion does not meet the standard requirements.

Problem Causes and Preventive Measures

The shell-and-tube heat exchanger has also become a heat retarder, which is mainly used in petroleum, chemical and other industries for medium heat exchange, and is one of the indispensable key equipment in the entire process.

Partial burn-through of the heat exchange tube at the tube head

Solution: During welding, it is strictly forbidden to strike and extinguish the arc on the pipe wall. The spot welding seam should be avoided and staggered by 90°, and the welding speed should be adjusted to make progress while maintaining stability.

Undercut or fusing of tube head heat exchange tube wall along the circumferential direction

Solution: Properly adjust the distance between the welding wire, the gun head and the heat exchange tube when welding, hold the welding torch with the right hand, feed the wire with the left hand, and use a stable posture to facilitate the welding of the tube head.

Root undercut of tube sheet and tube welds

Solution: Strictly follow the welding process when welding, and properly adjust the welding speed, wire feeding, current, gun head angle, etc. to ensure welding stability.

There is a difference in the height of the weld leg of the tube sheet and the heat exchange tube, the upper half circle is larger and the lower half circle is smaller in the circumferential direction

Solution: Place the heat exchanger vertically; make the tube sheet in a horizontal position, and use a platform or dig a pit to facilitate welding by the welder and ensure the quality of the weld seam.

Tube sheet and heat exchange tube welds have air holes

Solution: Grind the surface of the tube sheet, the groove, and the end of the heat exchange tube before welding to ensure that there are no sundries on the surface and reveal the true color of the metal. At the same time, the purity and flow of argon gas and the surface cleanliness of the welding wire are guaranteed.

Slowly rise and fall during welding, pay attention to the relevant factors in the arc ignition, finishing and welding process that affect the protection of the molten pool by argon.

The height of the welding leg is lower than the drawing requirements or the thickness of the welding seam is not enough

Solution: Strictly follow the welding process, use appropriate welding wire, welding speed, etc., to ensure the size of the welding leg.

2. The protruding length and expansion of the heat exchange tube

The protruding length of the heat exchange tube does not meet the requirements of the drawing

Solution: When making heat exchangers, the production process should be compiled in advance, and there are documents such as qualified welding evaluation and welding process documents for guidance. During the assembly process of the tube bundle, the production process is strictly followed.

At the same time, the inspection of process procedures is strengthened, and the next procedure can only be carried out after the inspection and inspection of each procedure is qualified.

Swelling problem

Solution: Before expanding the tube, the expansion joint process test and preparation of the expansion joint process should be carried out. When expanding the tube, the operator carefully implements the process and checks the expansion degree. If the tube does not meet the standard, the tube must be re-expanded.

The connection of heat exchange tubes and tube sheets is the most important link in the entire heat exchanger manufacturing process. Although there are many influencing factors, as long as more attention is paid to the inspection of the process during production, the pre-welding, welding, and welding procedures are strictly carried out in accordance with the requirements. Post-inspection procedures, you can ensure its quality clearance.