Long-term operation of PFA lined heating pipes under continuous high temperature, frequent temperature fluctuation and ultraviolet radiation will cause the molecular chain of PFA lining to break and crosslink abnormally. The lining gradually loses original toughness and becomes hard and brittle. Tiny cracks appear on the inner surface under medium scouring and pressure impact, which expand to form penetrating cracks. Corrosive medium directly permeates through cracks to contact the metal base pipe, triggering rapid corrosion and perforation of the substrate. This failure belongs to irreversible material aging damage of non-metal lining, which is a common hidden danger of lined anti-corrosion heating equipment under high-temperature working conditions.
1. Thermal Aging Brittle Crack Initiation Mechanism
PFA resin possesses excellent flexibility and anti-corrosion performance in its initial state. When exposed to long-term heat load exceeding the recommended service temperature range, thermal oxidative degradation occurs inside the material. Polymer molecular chains fracture continuously, plasticizer components volatilize and lose, the lining hardness rises sharply while elongation and impact toughness decline greatly. Under internal pressure, fluid scouring and thermal stress generated by expansion difference between lining and steel pipe, microcracks germinate at stress-concentrated positions such as lining pits and thin areas. Cracks extend along the thickness direction with temperature cycles until they run through the lining layer. Different from lining peeling caused by interface debonding, this damage is intrinsic performance deterioration of PFA material itself rather than bonding failure between lining and base pipe.
2. Typical Positions Prone to Aging Cracking
Pipe elbows and tee inner arc surfaces suffering long-term medium impact and stress concentration;
Liquid level alternation areas with repeated heating and cooling and obvious temperature difference;
Lining areas close to heat source with local overtemperature and concentrated heat radiation;
Pipe end flange lining edges with frequent assembly extrusion and external force squeezing;
Thin lining regions formed by uneven sintering thickness during processing.
3. Core Inducing Factors Accelerating Aging Cracking
Long-term overtemperature operation far exceeding the upper limit of PFA continuous service temperature;
Frequent sharp temperature rise and cooling leading to alternating thermal stress on the lining;
Oxygen-containing medium and ultraviolet irradiation accelerating thermal oxidative aging of PFA;
Excessive flow velocity causing strong fluid erosion and mechanical abrasion on the inner lining surface;
Inadequate lining thickness design resulting in poor anti-aging and anti-cracking allowance.
4. Full-Link Prevention and Control Technical Measures
① Strictly lock system working temperature below the rated temperature of PFA lining
Set up overtemperature interlock alarm to avoid long-term thermal degradation.
② Adopt gradient heating and cooling operation specifications
Forbid sudden temperature shock to reduce cyclic thermal stress on the lining.
③ Optimize pipeline flow rate to control medium scouring strength
Add buffer baffles at elbows to mitigate direct impact on the lining.
④ Guarantee minimum lining thickness during manufacturing
Supervise sintering forming process to prevent partial ultra-thin lining defects.
⑤ Arrange regular endoscopic internal inspection
Check crack and embrittlement conditions of the lining, replace failed pipes in advance.
5. Prevention Effect Comparison Table
表格
| Operation & Production Mode | Aging Cracking Risk | Application Suggestion |
|---|---|---|
| Long-term overtemperature + frequent temperature shock + no internal inspection | Rapid embrittlement cracking and medium penetration within service cycle | Stop operation and conduct internal endoscopic inspection immediately |
| Temperature controlled within standard range + gradual temperature switching + thickness compliance | Effectively slow down PFA aging and crack generation | Standard operation and manufacturing specification for PFA lined pipes |
| Thickened lining design + flow buffer structure + periodic internal detection | Extremely low brittle cracking failure probability | Preferred scheme for long-term high-temperature lined heating pipelines |
Conclusion
PFA lining brittle cracking failure is caused by thermal oxidative degradation of polymer materials under sustained high temperature and alternating thermal stress, leading to toughness loss and crack penetration. The core prevention strategies include limiting operating temperature to avoid thermal aging, reducing temperature mutation and medium impact damage, controlling processing lining thickness and carrying out regular internal detection. Whole-process control of production quality, operation parameters and in-service inspection can effectively prevent substrate corrosion leakage accidents induced by PFA lining aging cracking of heating tubes.
