Non-destructive testing personnel are qualified to perform NDT based on accumulated in-person or remote classroom training, in-person practical training, written and practical exams, and in some cases demonstration or qualification exams. Performance demonstration (PD) or Inspection Qualification (IQ) are interchangeable terms. NDT PD and IQ are supplemental to the core certification process that verifies the competency skills of an NDT technician. It demonstrates that the technician can follow an NDT procedure to perform an examination for a specific application and deliver acceptable results within the capability of the NDT method or technique utilized. This article explores the relation between NDT performance demonstration and AWS D1.1 and AWS D1.5 codes [1-2].
Introduction to Non-destructive Testing Performance Demonstration in Compliance with AWS D1.1 and 1.5 Code
Non-destructive testing of steel structures (think buildings) and steel bridges using ultrasonic testing (UT) and phased array ultrasonic testing (PAUT) is described in AWS D1.1/D1.1M Structural Welding Code - Steel, AWS D1.5/D1.5M Bridge Welding Code. The core NDT certification requirements are well defined and reference SNT-TC-1A and CP-189 guidelines. The qualification process for Ultrasonic Testing Level 2 requires a minimum of 80 hours of formal classroom training and 630 hours of on-the-job supervised practical experience. The qualify for Phased Array Ultrasonic Testing Level 2, an additional 80 hours of training beyond Ultrasonic Testing Level 2 is required. In addition, 320 hours of supervised on-the-job supervised practical experience is required.
Performance demonstration (PD) or Inspection Qualification (IQ) in compliance with AWS D1.1 and D1.5 is presented in the codes but with limited detail. AWS D1.8/D1.8M Structural Welding Code - Seismic Supplement does provide a detailed examination structure and grading scheme. This code is often used to evaluate the skill of ultrasonic level 2 technicians before they are approved to a project. In most cases, the entity administering the examination is independent from the non-destructive testing technician employer.
Overview of AWS D1.8 Performance Qualification Exam
The AWS D1.8 Structural Welding Code-Seismic Supplement outlines a performance qualification exam for ultrasonic technicians. The exam consists of at least 20 indications across multiple test specimens. An example test specimen is shown in Figure 1. The test specimen is a bridge girder flange simulation with two artificial discontinuities inserted into the weld. The first is a mid-wall lack of fusion approximately 0.50” long. The second is lack of root fusion also 0.50” long.
The NDT candidate must accurately assess the AWS D1.1/1.5 indication rating (IR) (decibels), weld flaw length, axial location relative to reference edge, and depth in the weld relative to top surface. The actual metrics cited above must be confirmed via two ASNT Level 3 UT inspectors.
The following metrics are used to determine assess the participant’s performance:
The indication rating (IR) must be within ± 6 dB
The indication length must be within +1” to -0.5”
The indication depth must be within ± 0.25”
To be considered a detected flaw, the candidate must satisfy at least two of the above metrics. Weld flaws that are detected with ultrasonic testing as well are passed on the overall rating assessment, R. The Overall Rating considers detected flaws “D” and false indication “F”. The following calculation is used:
(1) R=1/2 (1 +D – F)
To pass the exam the overall rating R must be 0.90 or higher, a detection rating D of 0.87 or higher, and a false indicating rating F of 0.15 or less. The candidate will pass the test if the detection rate is sufficient while the reject rate is minimal.
Phased Array Inspector Qualification to AWS D1.1 and 1.5 Code
Phased Array Ultrasonic Testing (PAUT) is a more advanced form of ultrasonic testing. It utilizes an array of ultrasonic transducers that can be electronically controlled to produce and receive ultrasonic waves at various angles and focal lengths. This allows for more precise and detailed inspections of welds and materials, including the ability to detect and size defects with greater accuracy. PAUT is often preferred for its versatility, speed, and ability to provide real-time imaging of the inspected area.
Personal qualification requirements for UT Level I, II, & PAUT level II are outlined in SNT-TC-1A. To receive these levels, you must reach the appropriate hours required per level. Along with the hours you must pass the appropriate practical exam administered by a UT level III or PAUT level III. The hours required are as listed. UT level I 40 Training hours and 210 method hours. UT level II 40 more training hours and 630 method hours. To take the PAUT level II you must be UT level II certified. PAUT level II 40 training hours with 320 method hours. These apply to AWS D1.1, D1.5, and D1.8.
Personal qualification requirements for practical exams according to AWS D1.5/D1.5M for PAUT. The exam would consist of two welded joints (e.g. butt, T, Corner) that have real or artificial discontinuities. These joints need to be examined using a phased array procedure written in accordance with AWS D1.5/D1.5M Annex J.
Phased Array Ultrasonic Testing (PAUT) Data
Figure 2: Example phased array ultrasonic testing for AWS non-destructive testing personnel qualification exam.
Example of PAUT data is shown in the figure above. The typical display for an Olympus X3 encoded scan shows the A-scan on the top left, S-scan in the top right, and C-scan across the bottom. The displayed PAUT A-scan is selected using the S-scan data cursor. The PAUT S-scan displayed depends on the C-scan data cursor.
When using UT and PAUT they use the same principles but when evaluating indications, they us difference premises. For UT you calculate the Indication rating. For PAUT you set three different levels to evaluate the accept or reject of an indication. Indication rating described from the AWS D1.1/D1.1M. The indication rating is the algebraic difference in decibels between the indication level and the reference level that is corrected for attenuation. Indication rating=d, attenuation factor=c, indication level=a, and reference level =b. the formula if the instrument has gain in dB: a – b – c = d. For PAUT evaluation the three different levels are Automatic Reject Level (ARL), Standard Sensitivity Level (SSL), and Disregard Reject Level (DRL). These levels can change based on the acceptance criteria, however for this example I will pull from AWS D1.5/D1.5M. the SSL will be aligned with the primary reference level dB at 50% ± 5% of Full Screen Height (FSH). The ARL is defined as 5 dB over SSL, and the DRL is defined as 5 dB under the SSL. All of these will be displayed on the A-scan of the PAUT unit. These levels break the A-scan into 4 classes class A, class B, class C, and class D. Class A is anything above the ARL. Class B is between SSL and ARL. Class C is between DRL and SSL. These classes correlate to the AWS D1.5/D1.5M table J.3 PAUT Acceptance Criteria as shown below.
Summary for Ultrasonic (UT) and Phased Array Ultrasonic Testing (PAUT) Performance Demonstration Exams
Non-destructive testing performance demonstration exams are emerging as important milestones for NDT inspection personnel across many different fabrication codes including AWS, ASME, and API. This article described the important features of AWS ultrasonic and phased array PDQs. In general, nondestructive testing performance demonstration exams in for ASME and API codes are comparable or more stringent.
References
AWS D1.1/D1.1M: American Welding Society, "Structural Welding Code - Steel," AWS D1.1/D1.1M:2020, Miami: American Welding Society.
AWS D1.5/D1.5M: American Welding Society, "Bridge Welding Code," AWS D1.5/D1.5M:2015, Miami: American Welding Society.
AWS D1.8/D1.8M: American Welding Society, "Structural Welding Code - Seismic Supplement," AWS D1.8/D1.8M:2016, Miami: American Welding Society.
SNT-TC-1A: American Society for Nondestructive Testing, "Recommended Practice No. SNT-TC-1A: Personnel Qualification and Certification in Nondestructive Testing," SNT-TC-1A:2020, Columbus: American Society for Nondestructive Testing.