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Integration of Production Data with NDE of Bridge Welds

Description:

The world-renowned quality expert Edward Deming said, “Routine 100% inspection to improve quality is equivalent to planning for defects, acknowledgement that the process has not the capability required for specifications. Inspection to improve quality is too late, ineffective, costly.” Deming promoted process control versus after-the-fact inspection, and he has been proven right by quality results and associated market disruption in many industries where process control has been used. The principle as described in this document is to integrate process controls and bridge fabrication NDE with the goal of improving overall production and reducing reliance on after-the-fact NDE.

Sensors are available to detect, measure and control nearly every variable that affects the quality of bridge welds. Preheat temperature and joint tolerances can be measured immediately before a weld is made. During welding, the voltage, current, travel speed and gas flow rates can all be measured and verified. Heat input can be instantaneously calculated. Importantly, the instantaneous voltage/amperage relationship of an ideally balanced arc can be compared to the actual welding output; deviations from the ideal conditions represent conditions that may result in weld quality problems. After the weld is made, the weld profile can be instantaneously read with lasers, identify visually-discernable weld quality problems, including undercut, undersized welds, poor weld profiles, etc. Finally, post weld NDE (including the newer PAUT outputs) can be linked and compared to the input characteristics.

This research will align with the following goals of the 2018 Strategic Plan of the AASHTO Committee on Bridges and Structures:

Goal 6 – Optimize Structure Systems – This project aligns with item 6.2.5. The use of production data will be the use of new technology to improve quality, reduce variation, and increase productivity in steel bridges.

Objective:

The research component of this proposal is to determine which quality related problems can and cannot be detected with process controls as compared to after-the-fact NDE. For example, the loss of shielding gas is readily detected with an imbalance in the voltage/amperage output characteristics that are part of modern welding power sources. Some forms of cracking are related to inadequate preheat, and the preheat sensors should enable detection of these problems. However, it is not currently known whether all bridge-quality concerns can be detected with process sensors.

This proposal involves the integration of the pre-weld sensor output, during welding output, post welding quality surface measurements and NDE results in a way that will enable better quality welds on a first pass basis, eliminating the creation of welds that require repair. For example:

1) Sensors that detect pre-welding conditions such as joint fit-up and profile, and preheat measurement can create “no-go” conditions that preclude welding until the conditions are corrected.

2) Sensors that measure arc instability can be used to shut down welding operations until corrected.

3) Sensors that detect weld surface profiles a foot or two behind a completed weld can stop welding operations if the output characteristics are non-conforming. For long welds, such as web-to-flange fillet welds, production can be stopped instead of the continued creation of less than ideal welds.

4) Linkage of NDE results to the production conditions (pre-weld, during weld and post welding sensor outputs) can help identify the conditions under which weld discontinuities are created, enabling adjustments to the acceptable pre-weld and during welding outputs.

5) The welding process controls described above can be used to identify portions of welds that are most likely to contain weld discontinuities, and therefore constitute the best use of our NDE resources. The output of sensor has the potential of “pointing fingers” to suspect welds.

6) As data is collected, it is probable that the need for new sensors will be identified that would further reduce the need for after-the-fact NDE.

7) Closed loop system could be developed to adjust welding output real time so as to eliminate conditions that result in weld flaws. Currently, seam tracking and joint volume measurement tool are being used to adjust robotic welding conditions to eliminate underfill and incomplete fusion problems.

Benefits:

Process control has the potential of significantly improving the first-pass weld quality and reducing the reliance on NDE that is currently a major means by which bridge Owners obtain confidence that their structures will perform as intended in service.

Tasks:

To be determined by research project panel

Implementation:

The results of this research will be implemented into national standards for fabrication, including the AASTHO/AWS Bridge Welding Code and AASTHO fabrication specifications. Also, draft specification language will be developed that state DOTs can use to adopt into their standard specifications.

Sponsoring Committee:AKB20, Steel Bridges
Research Period:24 - 36 months
Research Priority:High
RNS Developer:Ronnie Medlock, Member AKB20 and Duane Miller, Lincoln Electric
Date Posted:03/30/2021
Date Modified:04/20/2021
Index Terms:Nondestructive tests, Welds, Steel bridges, Process control, Fabrication, Inspection,
Cosponsoring Committees: 
Subjects    
Construction
Design
Maintenance and Preservation
Bridges and other structures

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