Practical Welding Today®
Radiographic and ultrasonic weld inspection
Establishing weld integrity without destroying the component
This article outlines the differences in radiographic and ultrasonic weld inspection, the two most common methods if nondestructive testing. It gives an overview of both methods, including how they are used.
Radiographic and ultrasonic weld inspection are the two most common nondestructive testing (NDT) methods used to detect discontinuities within the internal structure of welds. The obvious advantage of both of these testing methods is their ability to help establish the weld's internal integrity without destroying the welded component.
Radiographic testing (RT) usually is suitable for testing welded joints that can be accessed from both sides, with the exception of double-wall signal image techniques used on some pipe. Although this is a slow and expensive NDT method, it is a dependable way to detect porosity, inclusions, cracks, and voids in weld interiors.
RT makes use of X-rays or gamma rays. X-rays are produced by an X-ray tube, and gamma rays are produced by a radioactive isotope. The basic principle of radiographic weld inspection is the same as that of medical radiography. Penetrating radiation is passed through a solid object (in this case, a weld rather than part of the human body) onto photographic film, creating an image of the objectâ€™s internal structure on the film.
The amount of energy absorbed by the object depends on its thickness and density. Energy not absorbed by the object causes exposure of the radiographic film. These areas will be dark when the film is developed. Areas of the film exposed to less energy remain lighter. Therefore, areas of the object where the thickness has been changed by discontinuities, such as porosity or cracks, will appear as dark outlines on the film. Inclusions of low density, such as slag, will appear as dark areas on the film, while inclusions of high density, such as tungsten, will appear as light areas.
All discontinuities are detected by viewing the weld shape and variations in the density of the processed film. This permanent film record of weld quality is relatively easy to interpret if personnel are properly trained. Only qualified personnel should conduct radiography and radiographic interpretation because false readings can be expensive and can interfere seriously with productivity, and because invisible X-ray and gamma radiation can be hazardous.
Ultrasonic testing (UT) can be used on ferrous and nonferrous materials and often is suited for testing thicker sections accessible from one side only. In general, it can detect finer linear or planar defects than can RT.
UT makes use of mechanical vibrations similar to sound waves but of higher frequency. A beam of ultrasonic energy is directed into the object to be tested. This beam travels through the object with insignificant energy loss, except when it is intercepted and reflected by a discontinuity.
The ultrasonic contact pulse reflection technique is used in UT. This system uses a transducer, which converts electrical energy into mechanical energy. The transducer is excited by a high-frequency voltage that causes a crystal to vibrate mechanically. The crystal probe becomes the source of ultrasonic mechanical vibration. These vibrations are transmitted into the test piece through a coupling fluid, usually a film of oil, called a couplant.
When the ultrasonic waves pulse strikes a discontinuity in the test piece, it is reflected back to its point of origin. Thus, the energy returns to the transducer. The transducer now serves as a receiver for the reflected energy.
The initial signal, or main bang; the returned echoes from the discontinuities; and the echo of the rear surface of the test piece all are displayed by a trace on the screen of a cathode-ray oscilloscope. The detection, location, and evaluation of discontinuities become possible because the velocity of sound through a material is nearly constant, making distance measurement possible, and the relative amplitude of a reflected pulse is more or less proportional to the size of the reflector.
One of the most useful characteristics of UT is its ability to determine the exact position of a discontinuity in a weld. This testing method requires a high level of operator
Tuesday, December 9, 2008
Radiographic and ultrasonic weld inspection-Establishing weld integrity without destroying the component
Posted by BR at 10:29 AM
- [MW:1387] Welder qualification
- [MW:1391] BRAZING CS tube sheet to copper tube WPS...
- Quality inspections-Ensuring a top notch weld insp...
- Fatigue Failures
- Weld inspection before you weld-Using procedure qu...
- First line of defense-Educating welders to achieve...
- Entering a new phase in weld inspection-An introdu...
- A review of common nondestructive tests-Assessing ...
- Understanding weld discontinuities
- What welding inspectors should know about welding ...
- Radiographic and ultrasonic weld inspection-Establ...
- Material guidelines-Properties and characteristics...
- The fundamentals of gas tungsten arc welding: Prep...
- [MW:1392] CVN Impact exemption on PQR as per UCS 6...
- Tips for TIG torches-Simplifying torch assembly
- Joining aluminum with GTAW: Advice for the novice
- How to Improve Your Welds: Helpful hints for GMAW
- [MW:1393] Re: CVN Impact exemption on PQR as per U...
- [MW:1394] FW: Call for Registeration- National Wel...
- [MW:1395] Re: Calibration, Validation of welding m...
- GMAW vs. FCAW for beginners: Choose the best proce...
- Using narrow-gap GTAW for power-generation equipme...
- 10 frequently asked GTAW questions-Answers and exp...
- MIG welding tips and resources
- TIG welding - an overview
- The shocking truth about welding-A closer look at ...
- Guidelines for tungsten electrodes-Identifying, se...
- Arc welding discontinuities
- P is for plasma, precision-Requirements, qualities...
- Seeing GTAW through a new lens-Gas lens basics and...
- Welding austenitic stainless steel-Tips for optima...
- Welding ASTM A514 or A514M-05 steel?-Before you do...
- Stuck on SMAW?-Easy answers to 8 common electrode ...
- Great welds need the right gas
- The whats, whys, and whens of GTAW
- Tips for troubleshooting GMAW consumables-Gun and ...
- The lowdown on low-alloy filler metals-Your option...
- Welding hazards and how to prevent them
- GTAW common joint designs
- TIG for titanium tubing-Success hinges on filler m...
- [MW:1396] Re: Calibration, Validation of welding m...
- Microstructure of Steel
- [MW:1397] RE: 1312] Re: 1307] Re: 1305] welding re...
- [MW:1398] Equivalent PWHT
- [MW:1399] Re: Equivalent PWHT
- [MW:1400] Re: Equivalent PWHT
- [MW:1401] Interpass temperature measurement.
- [MW:1402] Re: Equivalent PWHT
- [MW:1403] Re: 1312] Re: 1307] Re: 1305] welding re...
- [MW:1404] Re: Interpass temperature measurement.
- [MW:1405] Re: Interpass temperature measurement.
- [MW:1406] Re: Equivalent PWHT
- [MW:1407] GOST 1050-88 CT 3
- [MW:1408] Branch components.
- [MW:1409] Re: GOST 1050-88 CT 3
- [MW:1410] Comparison of Vacpack electrode
- [MW:1412] Re: Comparison of Vacpack electrode
- [MW:1411] Re: Comparison of Vacpack electrode
- Metallographic Sectioning
- [MW:1413] Re: Interpass temperature measurement.
- [MW:1414] welding reqd on a weldolet
- [MW:1415] Re: welding reqd on a weldolet
- Resolving the challenges of welding coated steels
- [MW:1416] Re: welding reqd on a weldolet
- [MW:1417] Missing Information about reference to E...
- [MW:1418] ASME B31.3-2006 Ed. Fig. 328.5.2.c
- [MW:1420] Re: ASME B31.3-2006 Ed. Fig. 328.5.2.c
- [MW:1419] Re: ASME B31.3-2006 Ed. Fig. 328.5.2.c
- [MW:1421] Re: ASME B31.3-2006 Ed. Fig. 328.5.2.c
- [MW:1422] PWHT Requirement for clad plate vessel
- [MW:1423] Re: PWHT Requirement for clad plate vess...
- [MW:1424] Re: PWHT Requirement for clad plate vess...
- [MW:1427] Tray support ring on overlay
- Will your weld hold up? Discovering and preventing...
- Submerged arc welding : then and now
- Tips for TIG torches
- Metallurgical aspects of tube production
- Preparing, testing bend samples
- Modified GMAW for root passes
- Joining GMAW and GTAW
- SMAW Basicsâ€”How much do you know?
- First line of defense-Educating welders to achieve...
- Titanium You can weld it!
- Carbon content, steel classifications, and alloy s...
- Welding's effect on strengthening steel
- Making steels stronger
- It's all about why
- Welding cold-rolled steel to cast iron
- The root causes of weld defects
- Tack Welding
- Welding Symbols: A Useful System or Undecipherable...
- Failure Avoidance in Welded Fabrication
- Low Voltage Short Circuiting-GMAW
- Heat Treatment - What Is It?
- [MW:1425] Inspecting inaccessible piping -LRUT
- [MW:1426] NDT
- [MW:1428] Re: ASME B31.3-2006 Ed. Fig. 328.5.2.c
- [MW:1429] Re: ASME B31.3-2006 Ed. Fig. 328.5.2.c
- [MW:1430] Re: PWHT Requirement for clad plate vess...
- [MW:1431] RE: 1430] Re: PWHT Requirement for clad ...
- ▼ December (125)
- ► 2009 (2497)
- ► 2010 (5182)
- ► 2011 (4336)
- ► 2012 (3034)
- ► 2013 (3341)
- ► 2014 (2939)