Under-deposit corrosion perforation failure refers to impurities, sediment and scaling substances settling and adhering to the inner wall of the heating pipe to form a covering deposit layer. Liquid under the sediment cannot exchange with the mainstream medium, forming a closed occluded microenvironment. The local pH value drops and corrosive ions concentrate continuously, breaking the passive film of stainless steel and inducing localized pitting corrosion that extends through the pipe wall, resulting in medium leakage. This failure is hidden under surface fouling and hard to detect in daily visual inspection, widely occurring in heating circulation pipelines with poor medium filtration and long-term low-flow operation.
1. Corrosion Occlusion and Perforation Mechanism
After solid impurities deposit on the pipe inner wall, the covered area is isolated from the main fluid. Dissolved oxygen inside the deposit gap is quickly consumed by electrochemical corrosion reactions, turning the covered metal surface into an anode region prone to dissolution. Chloride ions and acid radicals in the mainstream medium continuously migrate into the sediment to balance positive charges, making the confined area highly acidic and corrosive. The passive chromium oxide film on 316 stainless steel is destroyed locally, and corrosion pits grow inward vertically. The sediment layer shields external pressure and flow scouring, allowing pits to expand steadily until wall penetration. Different from uniform internal corrosion of the whole pipeline, this corrosion only takes place beneath dirt deposits, while the exposed pipe wall remains intact basically.
2. Typical Positions Prone to Under-Deposit Corrosion
Bottom of horizontal pipelines where heavy impurities naturally settle and pile up;
Low-lying dead leg pipelines without medium circulation and long-term liquid stagnation;
Inner wall of heating coil pipes with low flow velocity and weak self-flushing ability;
Reduced-diameter pipe sections where flow slows down and particulate matter is easy to retain;
Pipe sections downstream of blocked filters with a large number of unfiltered impurities entering the system.
3. Core Inducing Factors Accelerating Corrosion Damage
Lack of filter equipment at the pipeline inlet, with raw medium carrying a large amount of suspended solids;
Long-term low-flow or intermittent shutdown operation leading to impurity precipitation and deposition;
No regular chemical cleaning or online flushing to remove accumulated sediment inside the pipe;
Medium containing chloride ions and acidic components that aggravate occluded area corrosion;
Excessively long pipeline stagnation period during system shutdown without drainage treatment.
4. Full-Link Prevention and Control Technical Measures
① Install multi-stage precision filter and dirt separator at the system inlet
Intercept particulate impurities from the source to avoid sediment generation.
② Set the minimum flow interlock program to forbid long-term low-flow stagnant operation
Use fluid scouring to prevent dirt from adhering to the pipe wall.
③ Formulate periodic circulation pickling and high-speed water flushing plans
Thoroughly strip deposited fouling before thick sediment forms occluded corrosion zones.
④ Add corrosion inhibitors and dispersants to the circulating medium
Disperse tiny particles and suppress electrochemical pitting reaction.
⑤ Arrange regular endoscopic inspection and wall thickness scanning on horizontal pipe bottom areas
Locate hidden corrosion pits under deposits ahead of leakage.
5. Prevention Effect Comparison Table
表格
| Operation & Protection Mode | Under-Deposit Corrosion Risk | Application Suggestion |
|---|---|---|
| No front-end filtration + no periodic cleaning + frequent shutdown retention | Hidden perforation leakage appears under sediment within operation cycles | Add filtering facilities and carry out full pipeline chemical cleaning |
| Inlet impurity interception + flow protection + fixed-cycle pipeline flushing | Effectively eliminate sediment deposition and occluded corrosion conditions | Standard operation specification for closed-cycle stainless steel heating piping systems |
| Online fouling monitoring + automatic periodic cleaning + fixed-point thickness detection | Extremely low hidden perforation leakage risk | Preferred scheme for continuous industrial heating circulating pipeline equipment |
Conclusion
Under-deposit corrosion of 316 stainless steel heating tubes is caused by sediment forming a sealed microenvironment that enriches corrosive ions and consumes oxygen, triggering localized pitting penetration under the dirt layer. The core prevention ideas are blocking impurity inflow via filtering devices, avoiding flow stagnation to reduce deposition possibility, regularly removing fouling deposits, adding chemical additives to inhibit corrosion and carrying out targeted hidden trouble detection. Whole-process management of medium pretreatment, operating parameter restriction and equipment maintenance can eliminate unexpected shutdown and medium leakage accidents caused by under-deposit corrosion of heating pipelines.
