Using DT X-Scan Detectors for Oil and Gas Pipes Inspection Applications

Table of Content

Introduction
Digital X-ray Inspection Techniques
Working Principle of a Typical X-Ray Imaging System
DT X-Scan Products
X-Scan ic4 Series
X-Scan iHE series
Conclusion

Introduction

Factors like cracking, internal and external corrosion, manufacturing flaws, and third party damage can affect oil and gas pipelines and other similar containers, exposing them to severe strain, stress, and other effects. As a result, non-destructive tests are increasingly being used to ensure quality in industrial areas. The quality of welding seams is a key point for quality assurance.

A number of current technologies are typically used for X-ray inspection, visual inspection, ultrasonic, magnetic particle, and other inspection techniques to assess the welds and ensure their quality.

A simple visual inspection be used to observe various weld defects such as cracks, porosity, incomplete fusion, incomplete penetration, overlap, inclusions, and edge melt. However in most of cases, visual inspection alone is not adequate because of the inner flaws. [1]

Ultrasonic weld inspection is based on the fact that high frequency sound waves beyond the range of human hearing can propagate in different materials, and be reflected by opposite wall surfaces and internal interfaces. Ultrasonic inspection is extensively used for nondestructive testing.

Its primary purpose is to detect and characterize internal discontinuities, but it can also detect surface discontinuities, measure thickness, and define bond characteristics. However, more methods may be needed to define acceptance or rejection.

X-ray weld inspection provides a unique benefit, as it is executed by pointing a radiographic source (a radioactive isotope or an X-ray tube) to the part of the weld that has to be inspected and by exposing for a digital detector or radiographic film to the radiation on the opposite side of the source tube or tip.

The resulting digital detector image or film contains data about the weld’s internal features. The image can be examined for all the related parameters to determine acceptance or rejection.

Compared to conventional photographic film, digital X-ray technology is now increasingly preferred. Its advantages include the ability to digitally transfer and improve images as well as time efficiency through bypassing chemical processing. In addition, less radiation can be used to create an image of similar contrast to traditional radiography.

Digital X-ray Inspection Techniques

The X-ray inspection technique, as used in the oil and pipe sector, has evolved from generating an image using a crude, noisy¸ low light phosphor screen that fluoresces when bombarded with ionizing radiation, to a clean, high-resolution image produced using digital imaging devices.

During this evolution, the X-ray image intensifier coupled to a CCD camera was utilized by the most extensively used technique. The image intensifier is a bulky device that weighs about 80 lbs and is developed using evacuated glass technology.

To put it simply, the image intensifier captures a low light image on a coated fluorescent input screen, changing the light energy to electron energy, and then accelerating the electron energy across an evacuation chamber to a smaller output fluorescent screen.

The image brightness is considerably increased by the acceleration of electrons [2], and it is subsequently converted back to light energy and captured with a CCD camera. The image is then displayed on a high-resolution monitor. The image intensifier offers a unique advantage by producing a live real time representation as the image is created at a video frame rate of 30 per second.

Although the image intensifier is still being used for the inspection in oil and pipe applications, it has certain limitations such as image blooming, limited dynamic range, high noise level, and relatively poor contrast.

The above issues can be resolved by using direct digital imaging devices. The digital imaging devices also provide a considerable improvement in contrast capability, a larger inspection area, and improved resolution in some cases. They are also robust and lighter in construction.

The digital imaging devices are two fundamental designs. One type is based on an amorphous selenium (a-Se) sensor or a flat panel amorphous silicon (a-Si) array. The panels’ active imaging area varies from 4 x 4" to 18 x 20". The physical size ranges from about 6 x 6" to 24 x 24" with a thickness of about 2"; and 15 lbs is the maximum weight.

The arrays are made using thin-film transistor technology and the pixel pitch differs from 100 to 400 µm. These devices are directly interfaced to a computer and the digital image is shown on a video workstation or the computer screen.

The other design is built on a linear diode array (LDA). This device features a row of imaging elements as opposed to the area array of the a-Se or a-Si. The input side of the LDA has a scintillation screen or a sequence of scintillating elements joined to a linear array of diodes.

The pitch between the diodes can differ from 0.2 mm to 2.5 mm. The element pitch is the key parameter that determines the LDA’s resolution capability. Theoretically, the length can be as long as needed. The LDA weighs only 4 to 8 lbs.

The LDA could be a much cheaper solution compared to the area array, and it also meets the needs for excellent signal-to-noise performance, high detection efficiency, and coverage. Additionally, LDAs can be used for many high-energy and low energy X-ray inspection applications. It can provide a suitable solution in high energy applications, as it delivers better crosstalk performance.[3]

Working Principle of a Typical X-Ray Imaging System

Figure 1 shows the operating principle of a standard imaging system with X-ray linear diode array (also known as line scan camera). X-ray linear diode array works on the same principle as a fax machine, which is sometimes known as a "push broom" operation. It captures a single line at a time (horizontal), and needs either the camera or the object to be moving to produce the vertical direction of the image.

Figure 1. The operating principle of a typical imaging system.

DT X-Scan Products

Over the last two decades, Detection Technology (DT) has developed X-ray Line scan cameras (X-Scan) for numerous X-ray applications. DT X-Scan, a linear-array X-ray detector, was designed as the imaging detector component for testing, inspection, and quality control instruments.

The imaging is based on shifting an object at a constant speed relative to the detector and an X-ray source, and collecting and storing a 2D X-ray image line by line. This also makes it ideal for weld inspection for oil and pipe applications.

Two X-Scan series are recommended based on the needs of oil and pipe applications - high energy-based X-Scan iHE series and X-Scan ic4 series with robust and compact design.

X-Scan ic4 Series

Figure 2. X-Scan ic4 product.

X-Scan ic4 series products have robust environmental design and come with industry-leading speed. They provide a low-cost solution for single energy industrial NDT applications with the smallest pixel size down to 0.2 mm. The high energy versions of ic4 work with the energy range of 160 KeV to 600 KeV, and the low energy versions are designed for the energy range of 40 KeV to 200 KeV.

X-Scan ic4 series products are relevant for applications, which need cost-efficient designs with the active length up to 614 mm and tough environmental enclosure. [4] Figure 3 shows the block diagram of the X-Scan ic4 series.

Figure 3. The Block diagram of a X-ray imaging system with X-Scan ic4

The following are general features of the X-Scan ic4 series products:

  • Active X-ray detection length from 102 to 614 mm which equals to the width of the conveyor
  • Scanning speed up to 4166 lines/s (equals to 3.3 m/s belt speed with 0.8 mm pitch)
  • Available pixel pitches: 0.2 mm, 0.4 mm, 0.8 and 1.5 mm
  • Data acquisition with USB 2.0 interface
  • Dynamic range > 8000, and 16-bit AD conversion
  • Versatile in industrial NDT applications with industry leading speed and sensitivity
  • Compact, waterproof enclosure with IP67 classification
  • USB interface support for multi-view systems (up to 4 pcs detector to single computer)
  • High tolerance (up to 6 K volts contact discharge) to electro static discharge (ESD)
  • High-performance and cost-effective DT photodiode and ASIC design
  • Enhanced features including binning function and temperature drift correction etc.
  • Interface library and demonstration software for application development

Table 1. General Characteristics of X-Scan ic4 series

General Characteristics X-Scan
0.2ic4
X-Scan
0.4ic4
X-Scan
0.8ic4
X-Scan
1.5ic4
X-ray tube voltage Vp range 40-200 kVp /
160-600 kVp
40-200 kVp /
160-600 kVp
40-200 kVp /
160-600 kVp
40-200 kVp /
160-600 kVp
Scintillator material GOS /CdWO4 GOS /CdWO4 GOS /CdWO4 GOS /CdWO4
Active area lengths 102–614 mm 102–614 mm 102–614 mm 192–576 mm
Number of pixels 512-3072 256-1536 128-768 128-384
Pixel pitch (spacing) 0.2 mm 0.4 mm 0.8 mm 1.5 mm
Pixel height 0.3 mm 0.6 mm 0.8 mm 3.2 mm
Pixel width 0.1 mm 0.3 mm 0.7 mm 1.4 mm
Maximum scanning speed 60 cm/s 167 cm/s 333 cm/s 625 cm/s
Min integration time 0.33 ms 0.24 ms 0.24 ms 0.24 ms
Interface USB2.0
Maximum integration time 128 ms
A/D resolution 16 bits
Dynamic range > 8000
Data digital interface 16 bits
Linearity/Non-linearity < 1%
Operational voltage +12 V DC
Power consumption 60 W max
Ambient Temperature 0 - 40 °C
Relative Humidity 30 – 80%
Storage Temperature -10 - 50 °C

 

X-Scan iHE series

Figure 4. A X-Scan iHE product

The X-Scan iHE series is a family of high-resolution linear array detector designed for NDT applications utilizing X-ray tubes up to 600 kVp energies. On special request, X-Scan iHE can be customized for high-energy tomography applications that utilize linear accelerators as radiation source.

Pixel sizes of 0.8 mm, 0.4 mm, and 0.2 mm are supplied as standard products. The active length can be easily modified due to the modular system structure. Coupled to low-leakage silicon photodiodes, pixelated cadmium tungstate (CdWO4) scintillator form the key detection element and the charge produced is read-out with DT’s proprietary low-noise ASIC circuits. [4]

X-Scan iHE series are relevant products, which are optimized for high-energy applications, and they provide the option of using linear accelerators up to 9 MeV. Figure 5 shows an example of block diagram of X-Scan iHE series mechanics.

Figure 5. The block diagram of an X-ray imaging system with X-Scan iHE detector

The following are general features of the X-Scan iHE products:

  • Active X-ray detection length from 410 to 1638 mm, which equals to the width of the conveyor
  • Scanning speed up to 1250 lines/s (equals to 1 m/s belt speed with 0.8 mm pitch)
  • Available pixel pitches: 0.2 mm, 0.4 mm and 0.8 mm
  • Dynamic range > 8000 and 16-bit AD conversion
  • High conversion efficiency, sensitivity, and dynamic range for complex high-energy applications
  • Cost efficient solution for industrial CT application
  • Data acquisition with Ethernet or frame grabber card interfaces
  • High-performance and cost-effective DT photodiode and ASIC design
  • Appropriate for both continuous and non-continuous sources
  • Interface library and demonstration software for application development
  • Customized solution available upon request

Table 2. General Characteristic of Standard X-Scan iHE series

General Characteristics X-Scan
0.2iHE
X-Scan
0.4iHE
X-Scan
0.8iHE
Notes
X-ray tube voltage Vp range 100-600 kVp 100-600 kVp 100-600 kVp 1)
Scintillator material CdWO4 CdWO4 CdWO4  
Scintillator thickness 3.15 mm 3.15 mm 3.15 mm 1)
Active area lengths 410-820 mm 410-820 mm 410-820 mm 2)
Pixel pitch (spacing) 0.2 mm 0.4 mm 0.8 mm  
Pixel height (PD) 0.3 mm 0.6 mm 0.8 mm  
Pixel width (PD) 0.1 mm 0.3 mm 0.7 mm  
Pixel height (scintillator) 1.57 mm 1.57 mm 1.57 mm  
Pixel width (scintillator) 0.16 mm 0.25 mm 0.6 mm  
Maximum scanning speed 5-10 cm/s 20-26.7 cm/s 40-53.3 cm/s  
Minimum integration time 2.0-4.0 ms 1.5-2.0 ms 1.5-2.0 ms  
Maximum integration time 128 ms 128 ms 128 ms  
A/D resolution 16 bits 16 bits 16 bits  
Overall uniformity
without offset at X-card level
< ±15% < ±15% < ±10%  
Overall uniformity
without offset at detector level
< ±20% < ±20% < ±15%  
Electronic crosstalk of each channel ≤0.5% ≤0.5% ≤0.5% 3)
Dynamic range > 8000 > 8000 > 8000 4)
Data digital interface 16 bits 16 bits 16 bits 5)
Interface Ethernet Ethernet Ethernet 6)
Linearity/Non-linearity < 1% < 1% < 1% 7)
Operational voltage +12 V DC +12 V DC +12 V DC 8)
Power consumption 60 W max 60 W max 60 W max  
Ambient Temperature 0 - 40 °C 0 - 40 °C 0 - 40 °C  
Relative Humidity 30 – 80% 30 – 80% 30 – 80%  
Storage Temperature -10 - 50 °C -10 - 50 °C -10 - 50 °C  

 

Note 1) 6 mm and 10 mm thick CdWO4 are also available upon request. With 6 mm and 10 mm thick CdWO4, the detectable energy range cab be 100 – 9 MeV.

Note 2) The active lengths of longer than 820 mm are also available upon request. There is no limitation on the max active length for customized X-scan iHE product.

Note 3) The electronic crosstalk of each channel is measured in ASIC level.

Note 4) Dynamic Range is defined as saturation signal/RMS Noise, with lowest gain setting (feedback capacitance is 3.5 pf) of ASIC. Available gain options are listed below: Available gain options are listed below:

i i i i i i i i i
GS0 0 1 0 1 0 1 0 1
GS1 0 0 1 1 0 0 1 1
GS2 0 0 0 0 1 1 1 1
Cf [pf] 2 3.5 3 2.5 2 1.5 1 0.5

 

Note 5) Digital interface uses 16-bit per pixel, but user can select actual output data to be 16,14,12,10 or 8 bits. The default value is 16-bits.

Note 6) Frame grabber card interface is available upon request.

Note 7) Non-Linearity is defined as max deviation from ideal response line defined by zero offset and signals at 80% of dynamic range.

Note 8) The operational voltage to be supplied to module. External power supply for 100-240 AC is provided with the module.

Conclusion

It has been proven that DT’s X-Scan detectors (LDA) fulfill the requirements of high detection efficiency, and superior signal-to-noise performance as the sub-system solution for X-ray inspection in oil and pipe applications.

Compared to other inspection methods, DT’s X-Scan detectors provide the following key benefits:

  • Compact and robust design for adverse environmental requirements
  • Suitable for both continuous and non-continuous sources in the range of 100 KV to 15 MeV
  • Cost-efficient solution in welding applications
  • Well controlled scatter and crosstalk ensures excellent image quality in high energy applications
  • Options for a wide coverage range of active X-ray detection length

Reference

1. Andreas Liessem, Fabian Grimpe, Ludwig Oesterlein "State-of The Art Quality Control During Production of Saw Linepipes" Calagary, Alberta, Canada, 4th International Pipeline Conference, 2002

2. Jianming Yu, Jiantao Niu "Imaging Technique of Computed Radiography and Digital Radiography" First Edition, Beijing, China Medication Technology, 2009, page 607-623.

3. Andreas BEYER, Holger LUX, Michael WÜSTENBECKER "Digital X-ray Solution For State-of-the-Art Radioscopic Testing of Weld Seams of Welded Steel Pipes According To DIN EN ISO 10893-7:2009-03" Ahrensburg, Germany, page 8-11, 2010

4. Detection Technology Inc. "X-Scan Linear-Array Detectors User’s Manual" 2009

This information has been sourced, reviewed and adapted from materials provided by Detection Technology, Inc.

For more information on this source, please visit Detection Technology, Inc.

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