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Piping of shell and tube heat exchangers

Release time:

2025-04-11

In the fields of petrochemical industry, power energy, shipbuilding, etc., shell-and-tube heat exchangers are like the "heat scheduler" of industrial systems, and the tube threading process is the core technology to ensure its efficient operation. The following is how to weave an efficient heat transfer network in "industrial needlework"

1. Prepare before threading the tube

a. Material and tool inspection

Pipe: Confirm that the material (such as 304 stainless steel, copper-nickel alloy), length, and outer diameter tolerance (±0.1mm) meet the design requirements.

Tubesheet: Check tubesheet hole diameter (usually 0.2 to 0.5mm larger than the outer diameter of the tube), hole spacing, and surface finish (Ra≤3.2μm).

Tools: threading guide, tube expander (mechanical/hydraulic), thickness gauge, cleaning brush.

b. Cleaning treatment

Clean the inner wall of the tube plate hole and the end of the tube with acetone or alcohol to remove oil and oxide layer.

Check the inner wall of the pipe without burrs (can be blown with compressed air).

2. The pipe operation process

a. Pipe preassembly

Insert the pipe through the side of the housing, pass through the baffle hole and the tube plate hole successively, and ensure that the clearance between the baffle and the baffle is uniform (0.5~1mm on each side).

Use the guide head to prevent the deformation of the tube end (especially the thin-walled tube), and the direction of the tube should be pushed from the fixed end (front tube plate) to the floating end.

b. Arrangement selection

Triangular arrangement (30°/60°) : High heat transfer efficiency, but difficult cleaning (suitable for cleaning fluids).

Square arrangement (90°) : easy to mechanical cleaning, low pressure drop (easy scaling conditions are preferred).

Corner square arrangement (45°) : Balance efficiency and maintainability.

c. Positioning and fixing

Temporarily fix both ends of the pipe after threading to avoid displacement.

Check the length of the tube protruding from the tube plate (usually 2~3mm, for welding or expansion).

3. fixed process selection

a. Welding fixation:

Application scenario: high temperature and high pressure conditions (such as steam heat exchanger).

b. Operating points:

Argon arc welding base, welding foot height ≥1.5 times the pipe wall thickness;

Post-weld penetration inspection (PT) or radiological inspection (RT) for cracks.

c. Expansion fixation

Application scenario: Low temperature and low pressure or easy corrosion conditions (such as seawater cooler).

d. Operating points:

Mechanical expansion: control expansion rate (3%~6%)

Hydraulic expansion: uniform pressure, suitable for thick tube plate

e. Welding expansion joint

First expansion to eliminate the gap, and then welding to enhance the sealing (commonly used in the petrochemical industry).

4. Quality inspection

a.Dimensional check

Pipe straightness deviation ≤1mm/m, full length deviation ≤3mm.

The coaxiality error between tube bundle and shell is < 2mm.

b.Tightness test

Airtight test: the shell is filled with 0.4~0.6MPa compressed air and coated with soapy water to check the leakage of the tube end.

Hydraulic test: 1.25 times the design pressure for 30 minutes, no pressure drop.

c.Heat transfer performance verification

Monitor the temperature difference between import and export in actual operation, compare the design value (deviation within ±10% qualified)