Inspection Trends

Nondestructive examination (NDE) personnel are qualified to perform inspections 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) and inspection qualification (IQ) are interchangeable. NDE, PD, and IQ are supplemental to the core certification process that verifies the competency skills of an NDE technician. It demonstrates that the technician can follow an NDE procedure to perform an examination for a specific application and deliver acceptable results within the capability of the NDE method or technique utilized. 

Introduction to NDE Performance Demonstration in Compliance with the AWS D1.1 and AWS D1.5 Codes

NDE of steel structures 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, and AWS D1.5M/D1.5, Bridge Welding Code. The core NDE certification requirements are well-defined and referenced in the American Society for Nondestructive Testing (ASNT) Recommended Practice No. SNT-TC-1A: Personnel Qualification and Certification in Nondestructive Testing, and ASNT CP-189, Standard for Qualification and Certification of Nondestructive Testing Personnel. The qualification process for UT Level II requires at least 80 hours of formal classroom training and 630 hours of on-the-job supervised practical experience. To qualify for PAUT Level II, an additional 80 hours of training beyond UT Level 2 is required. In addition, 320 hours of supervised on-the-job practical experience is required. 

The codes present PD or IQ in compliance with AWS D1.1 and D1.5 but with limited detail. AWS D1.8, Structural Welding Code — Seismic Supplement, does provide a detailed examination structure and grading scheme. This code is often used to evaluate the skill of UT Level II technicians before they are approved for a project. In most cases, the entity administering the examination is independent of the NDE technician employer.

Overview of AWS D1.8 Performance Qualification Exam

AWS D1.8 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 Fig. 1. The test specimen is a bridge girder flange simulation with two artificial discontinuities inserted into the weld. The first is a mid-wall incomplete fusion approximately 0.50 in. long. The second is the lack of root fusion, which is also 0.50 in. long.

The NDE candidate must accurately assess the AWS D1.1/D1.5 indication rating (IR) decibels, weld flaw length, axial location relative to the reference edge, and depth in the weld relative to the top surface. Two ASNT Level III UT inspectors must confirm the actual metrics cited above.

The following metrics are used to assess the participant’s performance:

• The IR must be within ± 6 dB
• The indication length must be within +1 in. to –0.5 in.
• The indication depth must be within ± 0.25 in.

For a flaw to be considered detected, the candidate must satisfy at least two of the above metrics. Weld flaws detected with UT are passed on the overall rating assessment, R. The overall rating considers detected flaws “D” and false indication “F.” The following calculation is used:

R = 1/2 (1 + D – F)

To pass the exam, the overall rating of R must be 0.90 or higher, the detection rating, D, must be 0.87 or higher, and the false rating, F, must be 0.15 or less. The candidate will pass the test if the detection rate is sufficient while the rejection rate is minimal.

PAUT Inspector Qualification to AWS D1.1 and AWS D1.5 Codes

PAUT is a more-advanced form of UT. It utilizes an array of electronically controlled ultrasonic transducers 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.

Personnel qualification requirements for UT Level I, II, and PAUT Level II are outlined in ASNT SNT-TC-1A. The candidate must reach the required hours per level to receive these levels. Along with the hours, the candidate must pass the appropriate practical exam administered by a UT Level III or PAUT Level III instructor. The hours required are as listed: UT Level I 40 training hours and 210 method hours and UT Level II has 40 more training hours and 630 method hours. To take the PAUT Level II exam, the candidate must be certified at UT Level II. PAUT Level II requires an additional 80 training hours with 320 method hours. These apply to AWS D1.1, AWS D1.5, and AWS D1.8.

The minimum personnel qualification requirements for practical examinations are outlined in AWS D1.5M/D1.5 for PAUT. The exam consists of two welded joints (e.g., butt, T, corner) that have real or artificial discontinuities. These joints need to be examined using a PAUT procedure written in accordance with AWS D1.5M/D1.5 Annex J.

Figure 2 shows an example of PAUT data. The typical Olympus X3 encoded scan display shows the A-scan in the top left, the S-scan in the top right, and the C-scan across the bottom. The displayed PAUT A-scan is selected using the S-scan data cursor, and the PAUT S-scan displayed depends on the C-scan data cursor.

UT and PAUT use the same principles, but when evaluating indications, they use different premises. For UT, the indication rating should be calculated. For PAUT, three levels are set to evaluate whether to accept or reject an indication. The indication rating described in AWS D1.1 is the algebraic decibel difference between the indication level and the reference level 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 is 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 — Fig. 3. However, for this example, I will pull from AWS D1.5. The SSL will be aligned with the primary reference level dB at 50% ± 5% of full screen height. The ARL is defined as 5 dB over SSL, and the DRL is defined as 6 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 four classes: A, B, C, and D. Class A is anything above the ARL; Class B is between SSL and ARL; Class C is between DRL and SSL; and Class D is anything below DRL. These classes correlate to the AWS D1.5 Table J.3, PAUT Acceptance Criteria, as shown below.

Summary

NDE performance demonstration exams are emerging as important milestones for NDE inspection personnel across many different fabrication codes, including AWS, the American Society of Mechanical Engineers (ASME), and the American Petroleum Institute (API). Coincidentally, the latter two demonstration exams are comparable or more stringent.

THOMAS R. HAY, PhD, P.E. (tomhay@techknowserv.com) is president of TechKnowServ Corp., State College, Pa. He is a licensed professional engineer and an ASNT Level III inspector.