Thermal oxidative aging brittle cracking failure refers to long-term service of PFA lining under continuous high temperature and oxygen-containing process atmosphere. The polymer molecular chain undergoes oxidative degradation and chain scission, making the fluoroplastic lose original toughness and gradually turn rigid and brittle. Under temperature alternation, medium pressure and tiny vibration, irregular cracks appear on the lining surface, which extend inward until complete fracture. Corrosive medium permeates the crack gap to separate lining from steel substrate, finally causing lining fragmentation shedding and base pipe penetration leakage. This damage belongs to irreversible chemical aging deterioration of fluoropolymer itself, mainly appearing in pipelines with long-term high-temperature continuous operation.
1. Oxidative Aging and Brittleness Mechanism
PFA long-term exposed to high-temperature aerobic environment will trigger free radical oxidation reaction on molecular backbones. Oxygen molecules attack carbon-carbon bonds in the polymer chain, breaking long molecular chains into short fragments, while generating polar oxidized groups. The original inter-molecular entanglement force decreases sharply, material elongation and impact toughness decline obviously, and the lining transforms from flexible tough state to hard brittle state. Microcracks germinate on stress-concentrated areas of the brittle lining under thermal expansion and contraction cyclic load. Cracks expand rapidly along the direction of molecular fracture without obvious plastic deformation. Different from thermal extrusion deformation caused by expansion coefficient mismatch, this failure stems from chemical molecular structure damage rather than pure physical dimensional deformation.
2. Typical Positions Prone to Thermal Aging Cracking
Direct heating sections closest to heat source with the highest long-term stable temperature;
Pipeline highest points where gas phase medium accumulates and oxygen concentration is high;
Elbows and bent parts bearing alternating bending stress during temperature fluctuation;
Thin lining areas with low material stock and faster aging degradation rate;
Pipeline sections frequently alternating between ultra-high temperature and room temperature shutdown.
3. Core Inducing Factors Accelerating Aging Failure
Long-term operation exceeding the upper limit of PFA continuous allowable service temperature;
High oxygen content in gas-liquid mixed medium continuously supplying oxidation reaction sources;
Addition of strong oxidizing substances in process medium to accelerate molecular chain breaking;
Unreasonable formula of lining raw material with insufficient anti-oxidation stabilizer content;
Long-term uninterrupted production without shutdown rest, lacking interval to slow down aging reaction.
4. Full-Link Prevention and Control Technical Measures
① Strictly lock the upper limit of long-term operating temperature
Forbid overtemperature running beyond the rated temperature range of PFA lining.
② Optimize process medium composition to reduce excess strong oxidizing components
Cut off the chemical driving force of oxidative degradation from the medium side.
③ Select PFA resin with anti-aging modified formula during lining customization
Add heat stabilizers to slow down molecular chain oxidation fracture.
④ Arrange regular intermittent shutdown and cooling maintenance periods
Reduce cumulative thermal aging damage through periodic temperature reduction.
⑤ Carry out regular endoscopic observation and flexibility sampling test on key aging-prone pipe sections
Replace seriously embrittled lining pipelines before crack generation.
5. Prevention Effect Comparison Table
表格
| Operation & Material Mode | Thermal Aging Cracking Risk | Application Suggestion |
|---|---|---|
| Long-term overtemperature + high oxidizing medium + no periodic maintenance | Brittle cracking and lining fragmentation occur within fixed service cycle | Replace with high-temperature resistant modified fluoroplastic lining |
| Temperature strictly controlled + medium oxidation degree limited + regular outage maintenance | Effectively delay molecular aging and brittlement process | Standard operation specification for high-temperature PFA lined heating pipelines |
| Anti-oxidation modified lining + real-time temperature interlock + annual lining performance inspection | Extremely low aging cracking hidden trouble | Preferred scheme for continuous production high-temperature anti-corrosion heating equipment |
Conclusion
PFA lining thermal oxidative aging brittle crack failure is caused by high-temperature oxygen erosion breaking polymer molecular chains, leading to irreversible embrittlement of lining material and stress-induced crack propagation. Core prevention measures include rigidly controlling service temperature, reducing oxidizing components in conveying medium, adopting anti-aging modified lining materials and arranging periodic shutdown maintenance and performance inspection. Whole-process control of material selection, process parameter management and equipment maintenance can eliminate leakage accidents caused by aging fragmentation of PFA lining heating tubes.
