Remote Visual Testing (RVT) for Internal Pressure Vessel Inspection
By Bruce A. Pellegrino, Visual Inspection Technologies, Inc.
Remote visual testing (RVT) of large surface areas (>1 m2) associated with vessel inspection requires a unique hardware approach compared to commercially-available borescopes, fiberscopes and videoborescopes. Faced with stricter OSHA regulations and the increased global competitiveness of today's marketplace, process facilities have looked toward a technical solution, including man-less entry into vessels, pressure vessels and tanks for their internal inspections. A unitized pan, tilt, light, color, zoom video inspection system was developed for use in confined-space, and hazardous-area locations associated with these components.
Recent history
Since the early 1970's, borescopes, fiberscopes and videoborescopes have been successfully applied to a very wide range of industrial inspection tasks including aircraft engines, nuclear steam generators, pharmaceutical tubing and border-crossing contraband detection. As a virtual spinoff of the medical instrument market place, industrial RVT has adopted and modified medical probe technology for suitability in the fast growing commercial sector. However, in the technical transfer of medical hardware to the larger-scale applications of petrochemical process units such as pressure vessels, mixers, tanks and steam drums, it became apparent that a scaled-up approach was necessary.
Additionally over the past several years, VT/RVT has been professionalized as an official NDT discipline by way of ASNT's TCIA Level-III testing and certification process. The end result of these efforts is that many industrial facilities are dramatically increasing the use of RVT.
OSHA regulation
Heavy industry, including power generation, refineries, chemical and process plants have historically sent personnel into large pipes, tanks, pressure vessels and mixing vats whenever routine or emergency inspections were needed. With the recent addition of U.S. Department of Labor's OSHA regulation, Process Safety Management (CFR 1910.119), inspection methodology, frequency and history must be documented by trained personnel. Figure 1 shows a typical Teflon-lined, pharmaceutical-grade vessel which is 8-ft dia. × 12-ft high, and with a 24-in.-dia. manway. Typical inspection includes verifying the integrity of plastic, stainless steel, refractory or glass linings, inspecting welded supports and assessing the condition of mixing blades, vanes and seals.
Numerous injuries and deaths have been documented over the years due to the hazards of heat, lack of oxygen, presence of toxic fumes and even failure of electro-mechanical systems such as gate valves. Additional OSHA regulations (CFR 1910.146) have made it illegal to send workers into confined spaces without significant safety systems in place including:
- Signs, work permits and written procedures
- Sign-in, sign-out books at worksite entrances
- Training in first aid, CPR, confined space entry, respiratory care and rescue
- GFI power
- Retrieval rescue equipment
- Air sampling instruments
- Vessel cleaning and purging procedures
- Blank-off, lock-out and tag-out of process vessels
Driven mainly by costs, many industrial facilities, through their safety departments, are following this letter-of-the-law and are using human entry into confined space as a last resort for inspection work. This is especially true in those intermediate range applications (12 - 24 in.-dia.) where human access is impractical.
Unfortunately, early attempts to employ medical-offshoot technology for large-area inspections were largely unsuccessful due to fundamental limitations associated with lighting, lensing and resolution in these small instruments. By the late 1980's, consumer preferences for smaller, lighter, higher-quality and lower-cost camcorders created a market demand that was filled by electronic giants such as Sony, Matsushita, Toshiba and Phillips. This multibillion-dollar business drove the development of higher-resolution CCD imagers, miniature lensing and a host of electronic image-processing and storage techniques which became readily available at reasonable cost to the industrial NDT markets. The huge R&D investments justifiable in a consumer electronics market, which could never have been made in the industrial inspection sector, became a technical windfall. All that was left to be done was packaging.
The elements of a suitable industrial RVT device include:
- Electronic imager—such as a charge-coupled device (CCD)
- Lensing—preferably variable focal length (zoom)
- Lighting—especially directional, focused white light
- Packaging—waterproof, small, light, corrosion-resistant
- Manipulation/positioning—mounts, poles and remote control of viewing direction
- Control cable—power, control & video signals
- Uuser interface—joystick operated, easy to use, video monitor
- Data storage—videotape of PC-based frame grabber
The Fig. 2 block diagram illustrates the design of a small (< 5.5-in.) pan, tilt, light, color zoom CCTV inspection system which is scaled to inspect 8–30-in.-dia vessels.
Fig. 3 is a 3-D rendering of the 5.5-in.-dia. pan, tilt, zoom (PTZ) head showing the framing angles available which allow detailed, close-up inspection of a component although the camera is 10–15 ft away. The remote PAN feature allows the inspector to sweep left and right; TILT permits looking up and down.
Field deployment
After several field deployments to test the camera's suitability in terms of sufficient resolution, magnification and lighting, it was determined that a proper positioning pole was needed to affix the camera's position at various locations in the vessel. Fig. 4 shows a swivel-base tripod with 1-in.-dia. carbon-reinforced plastic (CRP) support poles. The poles allow the PTZ camera head to be cantilevered into a vessel using a flange mount to secure the system.
CONCLUSION
The 5.5-in. dia. pan, tilt, light, color, zoom video inspection camera system has been successfully used to inspect several hundred vessels to date. Users report savings between U.S. $5,000–50,000 per deployment by not having to shut down or send personnel into these vessels. Additionally, a faster, safer, more thorough and better-documented inspection is achieved. The video images have been digitized and transmitted over the Internet to corporate engineering headquarters for analysis, archiving and trending. Further development work is being done so that the camera head can be deployed into Class I, Div. 1 hazardous locations as defined by the National Electric Code (NEC) and the National Fire Protection Association (NFPA).
Edited by Nick Basta
Bruce Pelligrino is president and GM of Visual Inspection Technologies.
For more information: Visual Inspection Technologies, Inc. 199 Highway 206 Flanders, NJ 07836. Tel: 973-448-0077.