API 570 Piping Inspection Services: Reliable Inspection & Integrity Solutions

Corrosion and Thickness Measurement in API 570 Inspection

Corrosion and metal loss are among the most important issues evaluated during many piping inspections. Internal corrosion can result from the process fluid, contaminants, water, chemicals, or changes in operating conditions. External corrosion can develop because of atmospheric exposure, damaged coatings, moisture beneath insulation, or other environmental conditions.

Ultrasonic thickness measurement is commonly used to determine the remaining wall thickness of piping components. Readings can be collected at selected locations based on the inspection plan and known damage mechanisms. Where historical measurements exist, current readings can be compared with previous results.

The inspection team may establish thickness-monitoring locations to track changes over time. These locations should be selected based on the piping system's configuration, expected corrosion mechanisms, service conditions, and previous inspection results.

Localized corrosion can require particular attention because isolated pits or areas of accelerated metal loss may not be adequately represented by a limited number of measurements. Inspection planning may therefore include additional readings where visual observations or service history suggest increased risk of localized deterioration.

Corrosion-rate calculations may be used where sufficient reliable inspection data is available. These calculations should account for the quality and location of previous measurements, inspection uncertainty, changes in operating conditions, and other relevant factors.

Where measured thickness approaches or falls below applicable minimum requirements, further engineering assessment may be required. Decisions about continued operation, repair, replacement, or other action should be based on appropriate technical evaluation rather than thickness data alone.

Non-Destructive Testing Methods for Piping Systems

Non-destructive examination can provide additional information when visual inspection and thickness measurements are not sufficient. The selected method should correspond to the suspected defect or deterioration mechanism.

Ultrasonic testing can be used for thickness measurement and, using appropriate techniques, for detecting certain internal or planar discontinuities. It is widely used in piping inspection because it can provide quantitative wall-thickness information without cutting or damaging the pipe.

Radiographic examination can be used in suitable applications to identify internal features or discontinuities in welds and components. Because radiography involves radiation, appropriate safety controls and qualified personnel are required.

Magnetic particle examination can identify certain surface and near-surface discontinuities in ferromagnetic materials. It may be appropriate for investigating welds or areas where cracking is suspected.

Liquid penetrant examination is designed to identify certain surface-breaking discontinuities on suitable non-porous surfaces. It can provide useful information about potential surface cracks that may not be clearly visible.

Other inspection technologies may be selected depending on the piping material, component geometry, access limitations, service conditions, and suspected damage mechanism. A professional inspection program does not necessarily require every NDT method; instead, methods should be selected according to the information needed to evaluate the piping.

Common Piping Damage Mechanisms

Understanding damage mechanisms is essential for developing an effective piping inspection program. Different services can produce different forms of deterioration, so inspection locations and methods should reflect the actual operating environment.

General corrosion can gradually reduce wall thickness over a broad area. Localized corrosion can produce deeper metal loss in particular locations. Pitting is one example of localized deterioration and may require focused examination.

Erosion can occur where high-velocity fluids, suspended particles, or turbulent flow conditions remove material from internal surfaces. Areas near elbows, reducers, control valves, and other flow disturbances may warrant attention depending on the process.

Corrosion under insulation is another concern in certain systems. Moisture can become trapped beneath insulation and contribute to external corrosion, sometimes without being immediately visible. Inspection planning may therefore consider insulation condition and service temperature when applicable.

Cracking mechanisms can also affect piping under certain combinations of materials, chemicals, temperatures, stresses, and operating conditions. Examples of damage mechanisms encountered in industry include fatigue-related cracking, thermal fatigue, stress corrosion cracking, and other forms of environmentally assisted cracking. The specific mechanism must be established through appropriate technical evaluation.

Vibration can contribute to mechanical fatigue and damage to supports, small-bore connections, and piping components. Changes in operating conditions or equipment performance may also introduce new vibration-related concerns.

Identifying the likely damage mechanisms before inspection helps ensure that inspection resources are directed toward areas where meaningful deterioration information can be obtained.

API 570 Inspection Planning and Intervals

Inspection planning should be based on the characteristics and operating history of the piping system. Factors such as service conditions, corrosion history, material, previous inspection findings, damage mechanisms, and applicable requirements can influence the inspection strategy.