How to Detect Corrosion on Pipeline Inner Walls?

Pipelines are widely used in industries such as petroleum,natural gas,chemical engineering,water treatment,construction,and energy.During long-term operation,the inner walls of pipelines are subjected to corrosion from fluid media,leading to wall thinning,reduced strength,and even leaks or explosions in severe cases.Therefore,regular inspection of pipeline inner wall corrosion is critical to ensuring production safety and extending equipment service life.

With advancements in modern inspection technologies,multiple advanced non-destructive testing(NDT)methods are now available to efficiently and accurately assess pipeline corrosion.This article systematically introduces common types of pipeline corrosion,detection methods,and their application scenarios to help enterprises and engineers select appropriate inspection solutions and ensure pipeline safety.

II.Common Types of Pipeline Corrosion

Before conducting corrosion inspections,it is essential to understand common corrosion types to select the most suitable detection methods.

1.Uniform Corrosion

oCharacterized by overall,even erosion of the pipeline surface by corrosive media,leading to gradual wall thinning.

oCaused by chemical or electrochemical reactions,common in pipelines transporting acidic or alkaline fluids.

2.Pitting Corrosion

oForms localized small pits or cavities on the pipeline surface,with significant depth that may cause perforation and leaks.

oPrimarily occurs in stainless steel or alloy steel pipelines,often triggered by chloride ions or sulfides.

3.Localized Corrosion

oOccurs in specific areas of the inner wall,such as welds,bends,or joints.

oCaused by fluid velocity changes,impurity deposition,or localized electrochemical potential differences.

4.Crevice Corrosion

oMainly occurs at pipeline connections,flange interfaces,or under seals due to oxygen concentration differences or localized acidic environments.

5.Stress Corrosion Cracking(SCC)

oCracks form under combined stress and corrosive media,degrading mechanical properties.

6.Microbiologically Influenced Corrosion(MIC)

oCaused by bacterial or microbial activity,common in sewage pipelines or marine environments.

III.Detection Methods for Pipeline Inner Wall Corrosion

Detection methods include traditional approaches and modern NDT technologies.

1.Traditional Methods

(1)Borescope Inspection

Insertion of optical or video borescopes to visually inspect corrosion.

Pros:Simple operation,visual clarity.

Cons:Limited to large-diameter pipelines;cannot measure wall thickness.

(2)Ultrasonic Thickness Gauge

Uses ultrasonic reflection to measure wall thickness and assess corrosion.

Pros:Portable,high accuracy,applicable to various materials.

Cons:Limited to point measurements;ineffective for overall corrosion assessment.

2.Modern NDT Technologies

(1)Ultrasonic Testing(UT)

Principle:Detects corrosion via ultrasonic wave propagation and reflection.

Methods:

oA-Scan:Measures wall thickness.

oB-Scan:Provides corrosion cross-sectional views.

oC-Scan:Generates 2D corrosion distribution maps.

Pros:

✔️High precision for various materials.

✔️Suitable for uniform corrosion detection.

Cons:

❌Blind zones in complex structures.

❌Requires coupling agents for wave transmission.

(2)Magnetic Flux Leakage(MFL)

Principle:Identifies corrosion defects by analyzing magnetic flux changes.

Pros:

✔️Fast inspection for large-scale steel pipelines.

✔️Suitable for in-service pipelines.

Cons:

❌Limited to ferromagnetic materials(not for stainless steel/alloys).

❌Requires advanced signal processing.

(3)Eddy Current Testing(ECT)

Principle:Detects corrosion via electromagnetic induction.

Pros:

✔️Ideal for non-ferrous pipelines(copper,aluminum,stainless steel).

✔️High-speed online monitoring.

Cons:

❌Limited depth for thick-walled pipelines.

(4)Radiographic Testing(RT)

Principle:Uses X-ray imaging to visualize corrosion and cracks.

Pros:

✔️High-resolution imaging for cross-sectional defects.

Cons:

❌Expensive equipment;requires shutdowns.

IV.How to Select the Right Detection Method?

Choose methods based on pipeline material,environment,and corrosion type:

Detection Requirement Recommended Method

Rapid overall corrosion assessment Magnetic Flux Leakage(MFL)

Uniform corrosion detection Ultrasonic Testing(UT),X-ray(RT)

Pitting/crack detection Eddy Current(ECT),X-ray(RT)

Visual internal inspection Borescope

V.Conclusion

Inner wall corrosion detection is vital for pipeline maintenance.Traditional methods(e.g.,borescopes,ultrasonic gauges)offer basic assessments,while modern NDT technologies(UT,MFL,ECT,RT)enable precise analysis.

Future advancements in AI,automated robotics,and big data will further enhance detection efficiency and accuracy,ensuring safer industrial operations.