Vacuum collapse failure refers to negative pressure being generated inside the pipeline during shutdown drainage, rapid medium emptying, pump sudden stop and system vacuum pumping. External atmospheric pressure is far greater than the internal pressure, and the flexible PFA lining cannot bear the pressure difference load. The lining is inwardly squeezed and sunken integrally or in large areas, tightly attached to the inner wall of the steel pipe and unable to reset. The flow passage is severely narrowed or fully blocked. In serious cases, the lining cracks under excessive compression stress, corrosive medium permeates the bonding interlayer, leading to large-area lining peeling and substrate corrosion leakage. This failure often occurs in negative pressure operation pipelines and process pipelines prone to internal vacuum after shutdown.
1. Pressure Difference Formation and Lining Collapse Deformation Mechanism
PFA lining only relies on sintered bonding force to attach to the steel pipe inner wall, and its own structural rigidity is weak. When the pipeline internal pressure drops below atmospheric pressure, a huge external pressure difference acts uniformly on the outer surface of the fluoroplastic lining. Once the pressure difference exceeds the critical anti-collapse bearing capacity of the lining and interface bonding force, the lining detaches from the steel pipe wall and caves inward. PFA has obvious viscoelastic creep characteristics; after being pressed and deformed under negative pressure for a certain period, it will produce permanent indentation deformation and cannot rebound to the original state even if the internal pressure is restored. Different from thermal stress buckling caused by thermal expansion constraint, this deformation is driven by external atmospheric pressure and internal pressure gap.
2. Typical Positions Prone to Vacuum Collapse Damage
Pipeline sections close to vacuum pumps and negative pressure extraction equipment with direct negative pressure action;
High-point blind pipes and dead legs where gas is pumped out and vacuum is easily formed during drainage;
Long horizontal pipelines with rapid liquid emptying, forming continuous negative pressure along the pipe axis;
Lining areas with pre-existing local degumming, which become the first collapse position under pressure difference;
Thin lining parts with insufficient structural stiffness and poor ability to resist external compression.
3. Core Inducing Factors Accelerating Collapse Failure
No anti-vacuum structural reinforcement design for lined pipelines used in negative pressure working conditions;
System operation lacks pressure balance venting measures during emptying and shutdown;
Sudden shutdown of conveying pump leads to siphon backflow and rapid negative pressure generation inside the pipe;
The bonding strength between lining and base pipe is insufficient in the prefabrication process;
Long-term maintenance of negative pressure state without timely pressure compensation and atmospheric balance.
4. Full-Link Prevention and Control Technical Measures
① Adopt grid anchor lining or thickened reinforced lining for negative pressure process pipelines
Improve the overall rigidity and anti-collapse performance of the lining structure fundamentally.
② Install atmospheric balance breather valves at pipeline high points and blind pipe ends
Supplement air in real time to eliminate internal negative pressure during liquid drainage and pump shutdown.
③ Optimize pump shutdown program to implement slow stop and valve sequential switch logic
Avoid instantaneous siphon effect and sharp pressure drop inside the pipeline.
④ Strictly control the sintering process to ensure uniform and reliable bonding between lining and steel pipe
Prevent local degumming that induces preferential collapse.
⑤ Prohibit long-term vacuum state without pressure compensation; regularly conduct endoscopic inspection of pipeline inner shape
Discover collapsed deformation at the initial stage and replace defective pipe fittings.
5. Prevention Effect Comparison Table
表格
| Design & Operation Mode | Vacuum Collapse Risk | Application Suggestion |
|---|---|---|
| Ordinary thin lining + no balance vent + sudden pump shutdown | Large-area lining collapse blockage occurs after one negative pressure formation | Retrofitting balance breathing device and replacing with anti-vacuum reinforced lined pipe |
| Reinforced anti-collapse lining + pressure balance configuration + standardized shutdown interlock | Effectively eliminate pressure difference load and irreversible lining sinking deformation | Standard design specification for negative pressure and vacuum process PFA lined heating pipelines |
| Built-in point anchoring lining + online pressure real-time monitoring + quarterly internal shape inspection | Extremely low caving blockage and lining separation leakage hidden danger | Preferred scheme for vacuum distillation and negative pressure feeding anti-corrosion heating pipe network |
Conclusion
PFA lining vacuum collapse failure is caused by internal and external pressure difference squeezing the flexible lining to detach and cave inward, resulting in permanent flow channel blockage. Core prevention measures include selecting anti-negative pressure reinforced lining structures, configuring pressure balance venting components, optimizing equipment shutdown control logic, guaranteeing interface bonding quality and avoiding long-term vacuum operation. Whole-process closed-loop management of pipeline customized design, auxiliary equipment matching and on-site operation specification can eliminate pipeline blockage and medium leakage accidents caused by negative pr
