Locations Where Delamination First Occurs in PTFE-Lined Heat Exchanger Cylinders Due to Thermal Cycling and Causes

1. The wet-dry interface zone (the most common location for blistering and delamination)

As the liquid level inside the heat exchanger cylinder rises and falls repeatedly, half of this zone is submerged in high-temperature liquid, while the other half is exposed to low-temperature steam or vapor. This area experiences the highest frequency of thermal cycling and the most frequent temperature shocks.

The thermal expansion coefficients of PTFE and the steel substrate differ significantly; repeated expansion and contraction generate alternating shear stress. Simultaneously, continuous evaporation and concentration at the liquid surface cause salts to penetrate the microscopic gaps between the lining and the shell, where crystallization and expansion force the interface apart, leading to the earliest appearance of blistering and delamination.

2. Stress concentration points at flanges, pipe bends, and corners of the shell

Flanges, inlet and outlet ports, temperature measurement ports, and spray ports are structural transition corners:

The steel substrate inherently contains residual stresses from casting or welding, and during PTFE lining formation, tensile and bonding stresses at these corners are already relatively high; under thermal cycling, stress at these corners is amplified, causing the interface bond to fail first, resulting in delamination and peeling starting from the root of the fillet.

3. Base of welded supports for internal supports and baffles

Internal baffles and anti-vortex supports are welded to the inner wall of the steel cylinder. The metal thickness at the weld points is uneven, and thermal expansion and contraction occur asynchronously. Micro-bubbles and bonding voids exist at the welded areas where the lining is applied. As temperatures rise and fall, the gas within these voids expands and contracts, causing continuous delamination of the lining along the weld seam.

4. Transition Zone Between End Heads and Straight Section of the Cylinder

The transition area between the curved end heads and the straight cylinder body experiences significant stretching during lining formation, resulting in lower bond strength at the interface compared to the straight sections of the cylinder. During overall temperature changes, the curved sections undergo greater deformation and displacement, leading to concentrated shear forces and preferential development of annular bulging and delamination.

5. The vapor-exposed zone at the top of the spray heat exchanger cylinder

The top is not wetted by the process fluid and is subjected to alternating exposure to low-temperature condensing vapor and high-temperature cylinder walls over extended periods. The lining undergoes continuous cycles of dry heat and rapid cooling without liquid-phase buffering. Consequently, the adhesive interface ages much faster than in fully submerged areas, and localized delamination gradually expands into larger patches.