Thomas R. Hay, Ph.D., P.E, ASNT Level #107162
498 Meckley Rd.
State College, PA 16801
June 30, 2020
The rope access technician (RAT) certification process is structured in a similar manner to non-destructive testing technicians. Where NDT technicians are certified through various central certifications programs like the American Society for Non-destructive Testing (ASNT) Central Certification Program (ACCP), rope access technicians are certifiable through Industrial Rope Access Trade Association (IRATA) and Society of Professional Rope Access Technicians (SPRAT). Similar to non-destructive testing personnel certification levels, there are comparable rope access technician levels. For example, a Level 1 technician is qualified to work while suspended from ropes under the supervision of a Level 3 RAT. A level 2 rope access technician may perform some limited rigging work and planning under the supervision of the Level 3. Finally, the Level 3 technician is responsible to the project rigging, equipment safety, rescue plans and project execution. This article discusses some of the more common non-destructive testing applications that are converging to rope access and provides some example NDT applications.
Advanced Non-destructive Testing Techniques
Non-destructive testing techniques can be broadly classified into conventional and advanced NDT techniques. Conventional NDT techniques include visual inspection (VT), liquid penetrant testing (PT), magnetic particle testing (MT), and some disciplines of ultrasonic testing (UT), eddy-current testing (ET), and radiographic testing (RT). Some important advanced NDT methods include acoustic emission testing (AE), phased array ultrasonic testing (PAUT), time-of-flight diffraction (TOFD), alternating current field measurement (ACFM), total focusing method / full matrix capture (TFM/FMC), guided wave ultrasonic testing (GWUT), and some disciplines of magnetic flux leakage (MFL) and eddy-current testing.
Safety and Access to Fracture Critical Structures
The number one goal for any project that requires NDT support is to ensure the safety of the NDT inspector and support crew while providing access to the fracture critical assets to perform the inspection in accordance with the contractual obligations. This section contrasts two different approaches to undertake an NDT inspection at a hydroelectric dam spillway. The spillway’s tainter gates control the spillway flow and contain many complete joint penetration (CJP) welded joints that are considered fracture critical. In order to perform non-destructive testing on the tainter gates, the gates must be shut completely so that the ground surface is relatively dry. Staging the spillway platform for non-destructive testing is an expensive proposition. While the tainter gates are accessible via a man-lift from the spillway runoff, a large crane is typically required to lower the man-lift down to the spill way at the start of the project and to extract the man-lift at the end of the project. An 80-ft manlift can require 140-ton crane, detailed crane lift plan, permitting, and significant transportation costs. The cost of simply delivering and extracting the man-lift can easily exceed the NDT inspection costs for some projects.
Figure 1 shows a TECHKNOSERV CORP. rope access ultrasonic testing level 2 technician performing phased array testing on a tainter gate fracture critical member. In this scenario, a two-man team accesses the gate using rope from the roadway or walkway above the gates. Significant cost savings are realized through elimination of heavy machinery rental, transportation, and traffic control.
Figure 1. Phased array ultrasonic testing (PAUT) preformed by a rope access technician.
Acoustic Emission Testing of Power Plants Piping
There are several critical components of power plants that are very susceptible to various time dependent damage mechanisms such as high temperature tensile failures, creep and rupture failures, hydrogen embrittlement, hot corrosion/erosion failures. Acoustic emission (AE) has been adopted in various structural health monitoring (SHM) platforms for critical components to detect the initiation and propagation of corrosion induced micro-cracking in high temperature high pressure pipelines and boilers, micro-fissuring due to hydrogen damage in waterwall tubes of condensers and as well as micro-cracking due to fatigue. Significant scaffolding must be erected to provide acoustic emission technicians access to all elevations the high temperature high pressure (HTHP) pipelines in order to install acoustic emission sensors. Depending on the powerplant configuration and vintage, the cost to erect the scaffolding may exceed the cost to perform the acoustic emission testing. In many cases, it is more pragmatic and cost effective to install the acoustic emission sensors, AE cables, and acoustic emission data acquisition hardware using a rope access team.
Figure 2. Rope access and alternating current field measurement (ACFM) for amusement parks.
Alternating Current Field Measurement (ACFM) and Amusement Parks
Amusement park non-destructive testing is largely a visual inspection process supplemented by magnetic particle testing and liquid penetrant testing. However, alternating current field measurement (ACFM) is trending to replace some visual inspection techniques where coatings prevent a thorough inspection or ride tear down and/or coating removable is undesirable. Staging for high elevation inspections at amusement parks can be a challenge due to limited roadways and access for large cranes. Many roller coasters exceed the reach of the largest man-lifts. The rope access inspections are often a necessity versus an economic alternative to cranes, man-lifts, or scaffolding. Figure 2 shows a rope access technician torqueing a flanged connection bolt and performing ACFM on various welds.
Advanced NDT for Bridge Non-destructive Testing
Phased array ultrasound (PAUT) and acoustic emission testing are applied to various fracture critical steel bridge structures. Phased array inspection is advantageous compared to conventional ultrasound because it provides: Full volumetric coverage of complex shapes from limited sensor positions and the ability to sweep ultrasonic angles increase probability of detection (POD), and reflections from defects or geometric features are color mapped according to their intensity and are easily sized against pass/fail acceptance criteria. Acoustic Emission technology has been utilized to provide risk-based inspection and maintenance for fracture critical members in infrastructure such as bridges and storage tanks. Acoustic emission technology provides real-time feedback on structural condition without the need for direct access to the area of interest. Access the bridge fracture critical members requires traffic control, and snooper trucks and other special access vehicles which impact total inspection cost. Rope access to fracture critical connections can be achieved from the roadway, or walkway, without traffic interruption or specialty access vehicles. As a result, acoustic emission inspection and phased array testing can be completed at comparable quality level for significantly less cost. The video shared below is compressed sample of the rope access bridge non-destructive testing experience.