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Development of Alternative Measures of Weld Quality

Description:

Non-destructive testing (NDT) is one of many practices used for assuring weld quality in structural welding; other practices include a) establishment of welding procedures, b) welder qualification, c) shop or erector certification, d) control of welding operations in fabrication and erection, d) visual inspection of completed welds, e) contractor supplied inspection, and f) optional inspection supplied by the owner. The commonly used NDT method is ultrasonic inspection (UT) although magnetic particle inspection (MT), radiographic testing (RT) and dye penetrant testing (PT) are also employed.

Typical NDT requirements are decades old. However, modern equipment and technology can be leveraged to help assure quality and reduce or eliminate NDT. Since 2010, welding equipment has been produced that records critical welding information, namely welding current and voltage. The amperage/voltage relationship can be used to identify the stability of the welding arc; instability in the arc may indicate the likelihood of weld discontinuities. Arc time, combined with a method of measuring the weld joint length (perhaps with laser measuring devices), could be used to determine travel speeds. With this data, heat input levels can be determined. Measurement of wire feed speeds and welding time could be used to determine melt-off rates, deposition rates, and joint fill rates. These data can be compared to the parameters associated with ideal welds, and non-conformances identified. For purposes of this proposal, the combination of this data is called the “electronic fingerprint” of the weld.

Conceptually, it may be possible for an ideal “electronic fingerprint” to reduce or even eliminate NDT requirements. Alternately, rather than performing NDT on 100% of the welded connections, a portion of the welds with a less-than-ideal “electronic fingerprint” may be identified for inspection.

The collection of welding current, voltage, wire feed speed, and the current/voltage interaction has been established. Travel speed measurements have not been established for semi-automatic welding (this data has been collected from robotic systems). The linkage of this data to conditions where weld defects are created has not been established.

Objective:

The objective of this research is to establish an alternative measure of weld quality that would eliminate or reduce reliance on conventional NDT. For welds that fail to meet the criteria for the alternate system, conventional NDT could be used.

Benefits:

The time and expense associated with NDT can be viewed as an expense that adds limited value. Certainly, when the quality of welding is such that no defects are detected by NDT, it is difficult to assign value to such activities. Using “electronic fingerprints” to accept welds with a high probability of acceptable quality could reduce these non-value added inspection costs considerably. Identifying welds via the “electronic fingerprint” that are likely to have quality problems and designating those welds for NDT would result in resources being directed to specific welds in an intelligent manner.

Estimating savings associated with reduced or eliminated NDT is difficult. A conservative estimate suggests that 3-5% of the fabrication cost associated with bridge girder fabrication is associated with NDT. More difficult to estimate is the cost in terms of factory throughput, particularly with RT is required.

Tasks:
  1. Survey the welding industry and identify available electronic data. Identify unavailable information.
  2. Investigate methods to obtain missing data (such as travel speed).
  3. Conduct a series of welds using idealized welding parameters as well as sub-optimal condition. Using conventional UT, compare the “electronic fingerprint” of good and bad welds.
  4. In a blind test, produce weld with acceptable and unacceptable “electronic fingerprints” then validate the model with conventional UT.
  5. Propose code language for incorporation into AISC and AWS standards that would permit the use of this alternate approach to weld quality management.
Sponsoring Committee:AKC70, Fabrication and Inspection of Metal Structures
Research Period:24 - 36 months
RNS Developer:D. Miller, R. Medlock
Date Posted:03/31/2020
Date Modified:05/08/2020
Index Terms:Nondestructive tests, Automatic welding, Weld strength, Weld tests, Welding, Welds, Weldments, Data collection, Quality assurance,
Cosponsoring Committees: 
Subjects    
Highways
Construction
Materials
Bridges and other structures

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