How to Test the Corrosion Performance of Flanges

Flanges are used in industrial structures primarily to improve connections and maintain leak-proof steel pipelines. However, many flanges corrode and age after a period of use, losing their sealing performance. Therefore, it is essential to regularly test flanges for corrosion. Here, we share the process for measuring flange corrosion.

First and foremost, it is crucial to emphasize the importance of regular maintenance and inspection of flanges. Corrosion typically manifests as thinning of the flange wall, with localized pitting. The causes and mechanisms of internal corrosion in stainless steel flanges require specific methods and principles for analysis. Currently, the most widely used flange corrosion detection methods both domestically and internationally are magnetic flux leakage testing and ultrasonic testing.

Ultrasonic Testing: Ultrasonic testing utilizes the principle of ultrasonic pulse reflection to measure the thickness of the corroded steel pipe wall. The basic principle of magnetic flux leakage testing is based on the high magnetic permeability of ferromagnetic materials. The magnetic permeability at the corrosion defect site of a flange is much lower than the flange's overall permeability. When the flange is magnetized by an external magnetic field, most of the magnetic lines of force pass through the steel pipe when there are no defects, resulting in a uniform distribution. However, when there are defects inside the flange, the magnetic lines of force bend, and some leak out onto the steel pipe surface. Detecting the leakage flux escaping from the magnetized flange surface determines the presence of the defect.

Additionally, during testing, an ultrasonic pulse is emitted perpendicularly towards the inner wall of the flange. The probe first receives the reflected pulse from the inner surface of the steel pipe wall, and then receives the reflected pulse from the outer surface of the steel pipe wall. The distance between this reflected pulse and the reflected pulse from the inner surface reflects the thickness of the steel pipe wall. In actual testing, elbows need to be inspected according to the specific conditions and instructions, following the methods used in ultrasonic testing. Ultrasonic testing is also applicable to the thickness measurement and metal property testing of other metal structural components.