Phased-array ultrasonic testing (PAUT) is making its way into the steel bridge world. This is a form of ultrasonic testing (UT) in which an array of transducers in a single housing are fired in sequence to create, steer, and focus a particular waveform to detect discontinuities. PAUT may be encoded, which means using a wheel or similar device to trigger data collection automatically, including position of the probe, along the travel path of the probe.
PAUT is new to the bridge industry but is not new technology. Its use in lieu of radiography (RT) has been accepted in the tank and pressure vessel industries for years. Ongoing research conducted by FHWA indicates that PAUT can be used to assure similar levels of weld quality as conventional NDE methods.
Pending AASHTO balloting, PAUT is expected to appear as a standardized UT method in the next edition of the AASHTO/AWS D1.5 Bridge Welding Code. Use of PAUT in lieu of RT in D1.5 will initially be only with the Engineer’s approval. Florida DOT has already adopted provisions similar to the D1.5 provisions, becoming the first DOT in the country to fully embrace this technology.
There are a number of reasons to prefer UT to RT. Foremost is the safety hazard that accompanies RT and the significant disruption to the fabrication process that this safety hazard causes. In addition, UT is superior to RT in detecting planar discontinuities such as tightly closed cracks or lack of fusion. However, conventional UT has drawbacks that have led RT to be the default butt weld NDE method in D1.5. UT is highly dependent on operator skill and technique; the operator must analyze the scan in real time; and conventional written UT reports, unlike radiographs, present little or no visual information about the weld and do not capture the entire weld, only rejectable or “recordable” areas.
However, unlike conventional UT, encoded PAUT using scans or combinations of scans that cover the full weld volume can be used to build a three-dimensional map of detected discontinuities within the weld. The data can be analyzed at the time of scanning or later. The semiautomatic or even automatic nature of encoded PAUT means that, except for some supplemental manual scanning that must be performed, the individual operator’s technique in manipulating the probe is no longer a significant consideration. Sectorial scans sweeping through multiple angles can enhance the detectability of discontinuities at different orientations. (Rejectability, as always, depends not just on detectability but on acceptance criteria.)
The addition of PAUT to the next edition of D1.5 will facilitate faster, safer, and more accurate investigation of full-penetration welds. Later, additional research through NCHRP will take even further advantage of PAUT by helping establish acceptance criteria based on “fitness for purpose” concepts that will make investigations smarter and avoid unnecessary repairs. Expect to see this technology appearing on shop floors as fabricators adopt it and technicians gain qualifications.
Heather Gilmer, P.E. is the Quality Assurance Manager at Tampa Tank Inc. - Florida Structural Steel
Alex Wilson Announces Retirement from ArcelorMittal
After 41 years of dedicated and outstanding service to the plate business, Alex Wilson, Division Manager, Customer Technical Service, has decided to retire on May 31, 2015. After obtaining his Bachelor’s and Master’s degree in metallurgy from MIT, where he was also a standout basketball player, he worked for Corning Glass and Westinghouse before joining Lukens Steel’s research division in 1974. Wilson has been the driving force and the leading expert behind the development of low sulfur technology in plate steels as well as the application of weathering and high performance steels for bridges and multiple product development efforts, such as HSLA- 65/80/100, for the Navy.
Wilson is extremely well respected in the industry, having held numerous leadership positions in organizations like ASTM, The Bridge Task Force, The National Steel Bridge Alliance and the AISI Market Development Committee. His contributions to the industry have been recognized numerous times, including being named a fellow of ASM International in 1985 and most recently receiving the prestigious Lifetime Achievement Award from the AISC.
American Petroleum Institute Provides Interactive Gas Tax Map
The 2016 World Steel Bridge Symposium, to be held April 13-15, 2016 in Orlando, Florida, is now accepting papers for presentation. The organizers of the 2016 WSBS are interested in papers that deal with all aspects of steel bridge design and construction. Papers will be requested based on acceptance of abstracts of 500 words or less. Below is a list of important information.
- Preferred format is a pdf attachment.
- Send abstracts to email@example.com
- Abstracts are due by June 5, 2015
- Authors will be notified of acceptance by July 17, 2015
- Completed papers for review must be received by November 13, 2015
The World Steel Bridge Symposium brings together design engineers, construction professionals, academicians, transportation officials, fabricators, erectors, and constructors to discuss and learn state-of-the-art practices for enhancing steel bridge design, fabrication, and construction techniques.