Nondestructive testing methods used in bridge inspection

Visual inspection – this is the most common form of non-destructive testing as they don’t need any special testing equipment. It can be done quickly and is more economical than the other non-destructive methods but the subjective nature of visual inspection can produce variable and inaccurate results.

 

Digital image processing – Earlier two methods Neuro-Fuzzy Recognition Approach method (NFRA) and the Simplified K-Means Algorithm (SKMA) method (Lee 2011) were developed to recognize surface defects like rusting by using digital color imaging processes. 

 The NFRA methods utilized artificial intelligence to separate rust pixels from the background pixels while SKMA method utilized a statistical approach to separate object pixel from the background pixels. These methods couldn’t generate reliable results under specific environmental conditions. Later on, another advanced method rust-color-spectrum-based rust defect-recognition method (RUDERM) was developed which utilized color space unlike greyscale images used in earlier methods to identify rust spots and discriminate it from the background and other defects (Shen et al. 2013).

The eddy current method – It works on the electromagnetism principle and utilizes electromagnetic induction to detect defects in conductive materials. It has several advantages which makes it a practical option for field inspection. One of the advantages is that it can penetrate both conductive and non-conductive steel coatings to identify underlying cracks without damaging the integrity of the coating system of the bridge.

Radiographic method – This is the oldest and traditional approach to non-destructive testing. It is similar to X-ray testing and used to inspect the quality of the butt welds. In this method, penetrating radiation is absorbed to generate a high contrasting image indicating the cracks and discontinuities in the welds. Although this is an effective method but the high radiation can be harmful to the inspection crew and the public.

 

 

Ultrasonic testing

This method works on high-frequency sound waves to detect and size the defects in the welds. Advancement in this method made it automated which utilizes robotics to ensure complete coverage of the area under inspection and minimize human interaction (Badar 2008). It can easily locate surface and subsurface defects but requires high skills to operate the system.