Home > Defect Evaluation

1. Discrimination and evaluationof defect for material and technology 

In the process of industrial manufacturing, various defects inevitably appear in the internal of workpiece, such as pores, cracks, looseness, shrinkage, inclusion and slag inclusion, etc.

Traditional methods such as ultrasonic testing and magnetic particle testing have limitations. It can’t get detailed information of defects such as types, dimension and location using traditional methods and it is difficult to make an accurate evaluation.

Industrial CT systems can realize diversified non-destructive functions for various workpieces with different material or different structure. Industrial CT systems can acquire CT images of workpiece after scanning. The images are saved as digital images and processed by customized software, and then internal defects of workpiece can be clearly displayed. According to the distribution characteristics of gray scale in the region of defect, type of defect can be recognized. Dimension, area and location of defect can be acquired by measurement function, which are benefitial to evaluate defects accurately.

Three-dimensional images can be constructed based on two-dimensional CT image by using the corresponding 3D reverse software, which can benefit to observe 3D shape of defect, to realize 3D measurement and localization, and to make a final evaluation. 

1.1Inspection points for industrial CT systems

CT image is a cross section image of workpiece obtained by industrial CT systems, and the defect displayed in CT image shows 2D distribution in cross section of workpiece.

The image grey value is proportional to X-ray radiation attenuation coefficient of workpiece which is determined by physical principle of industrial CT system. It can also be considered that the image grey value is approximately proportional to the density of workpiece. Defects can be detected when there is density difference between defects area and background area. Otherwise, defects can’t be detected in CT image.

An industrial CT systems has certain specifications. Defect can not detected when its dimension or density difference is less than specifications of industrial CT system. That is, Range of defect dimension or density difference should not be beyond the detection ability of the industrial CT system.

1.2Difference between defect and internal structure in CT image

It is needed to distinguish difference between defects and internal structure in CT image due to the defect in CT image is shown depending on the difference of gray value, which can be confused with internal structure of workpiece.

 

 

Area

Edge shape

Gray of edge

Defect

Smaller

Irregular

Existing irregular gray transition area

Structure

Bigger

Simple and regular

Having clear gray edge

1.3Features and legends of CT image for diversified defects

It is needed to know various features of defects and gray distribution in CT image, and then correctly distinguish type of defects.

 

Type of defect

Features

Features of CT image

Legends of CT image

Pores

With simple void edge and small size

Low density, small area with clear and simple edge appears in high density area. The gray value of small area is consistent, and close to the gray value of air surrounding workpiece.

Pores with different diameter on the pore Phantom 

A pore near surface of steel casting

 

Shrinkage

With irregular cavity edge and lager size

Low density area with complex edge appears in high density area. And its area size is bigger. The gray value of low density area is consistent, and close to the gray value of air surrounding workpiece.

Casting shrinkage of railroad parts

 

Looseness

Void area isn’t consistent, and size is bigger.

Low density area with complex edge appears in high density area. And its area size is bigger. The gray value in this area isn’t consistent, which is higher than the gray value of air surrounding workpiece.

Looseness of workpiece

 

Crack

It is a narrow and hollow defect. Shape and direction of defect is random. 

Low density area with narrow edge appears in high density area. Width of this area is very small, and its length isn’t being limited. The gray value in this area is close to the gray value of air surrounding workpiece.

Crack in a rock sample

 

Debonding

It is a narrow and hollow area which extends along adhesive interface.

Debonding is similar to the crack, and it is located in adhesive interface. Its shape is regular,  such as straight line, arc, etc.

Two debondings in a sample

 

Inclusion

It is located inside workpiece.

Granular low density area or granular high density area is located in workpiece.

High density inclusion in a rock sample.

 

 

2.Evaluation service system of defects

   

2.1Evaluation service system of defects for industrial CT systemAs the most advanced NDT system, industrial CT system can realize various NDT functions for various material workpieces or various dimension workpieces. It can accomplish the interpretation for internal structure of workpiece and identification and evaluation of defect according to the CT image, which the identification and evaluation of defect is the most basic goal of NDT.

 GRANPEC has built evaluation service system of defects inspected by industrial CT system, and has formed mature and efficient X-ray NDT solutions based on the goal of defect evaluation.

 

Basis

Stages

Measures for evaluation service system of defects

Characteristics of inspected workpiece, such as dimension, structure, density, type and size of defect

Designing stage of industrial CT system

Adopting customized design, including parameters of X-ray source, detector, and mechanical layout in CT system to meet the inspection requirements.

Researching and manufacturing stage of industrial CT system

Strictly ensuring quality of hardware, and developingdigital image processing software with various general and special functions according to the characteristics of the defect area in digital image in order to realize more effective defect recognition, measurements function for dimension and density.

Delivery and using stage of industrial CT system

Assisting users to complete research and development of detection technology, and realizing reliable and efficient detection for various types of defect.

After-sale service stage of industrial CT system

Providing related technology support according to the customer’s requirements.

 

 2.2Function of defect evaluation software for industrial CT system  

Image inspection & processing software of industrial CT system is the direct tool to realize defect evaluation, and use of software functions is an important part of effective evaluation defects.

 

Evaluation methods

Functions

Evaluation standard

Visual

Defect is found by visual method, and its type, dimension and location can be estimated from CT image.

CT image is processed by image processing software, which makes detail information of image more clearly in ROI (region of interested) and gray area of ROI. It benefits to visually observe and effectively estimate the defect information.

 Image processing software includes diversified generally functions of digital image and some special functions for defects image processing.

Evaluation standard of defect is decided by user. Defect levels and workpiece quality can be evaluated based on specific interpretation standard of defect in NDT industry.

Dimension measurement

Dimension information and location information of defect can be acquired by dimension measurement functions of image processing software.

The image processing software includes diversified dimension measurement functions, such as length, diameter, area, angle and wall thickness, etc. The precision of dimension measurement is about 0.1mm.

Density measurement

Density information of workpiece can be acquired by density measurement function of image processing software.

Density measurement in ROI can be realized by calibration method.