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CORROSION DETECTION DEVICES

Boyd D. Howard

Senior Fellow Engineer

Co-authors: Dr. Kenneth Gibbs and James B. Elder III

Westinghouse Savannah River CompanyArmy Corrosion Summit--2004

December 2003

Westinghouse Savannah River CompanyAiken, SC 29808

PREPARED FOR THE U.S. DEPARTMENT OF ENERGY UNDER CONTRACT

DE-AC09-96SR18500


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Corrosion Detection Devices

Boyd D. Howard

Senior Fellow Engineer

Co-authors: Dr. Kenneth Gibbs and James B. Elder III

Westinghouse Savannah River Company

Army Corrosion Summit--2004

ABSTRACT

Nondestructive Examination Systemsspecialists at the Department of EnergysSavannah River Site have unique, remotelycontrollable, corrosion detection capabilities.

The corrosion detection devices most frequentlyused are automated ultrasonic mapping systems,digital radiography imaging devices, infraredimaging, and eddy current mapping systems.These devices have been successfully utilized ina variety of applications, some of which involvehigh levels of background radiation. Not only iscorrosion located and mapped but other types ofanomalies such as cracks have been detected andcharacterized. Examples of actual corrosion thathas been detected will be discussed along withthe NDE systems that were used.

Westinghouse Savannah River Company, aprime contractor to the Department of Energy,has collaborated with other government agenciesin conceiving, designing, fabricating, deploying,and supporting automated inspection devices.The collaborative working relationships, whichWSRC has had with other government agencies,have been highly successful and very beneficial.In every case technology has been transferred inboth directions; thus benefiting both agencies.

INTRODUCTION

The fact that metals corrode does not come as asurprise to anyone. Corrosion affects all of us.Many of the things that are corroding aggravateus and cost us money. It has been reported thatcorrosion costs in the United States alone areestimated to be close to $300,000,000,000 ayear, or approximately 3.2 percent of the U.S.gross domestic product.

Those who live in states where they put salt onthe roads to melt snow and ice must diligentlymonitor the condition of their automobiles orthey end up with side panels like the one shownin figure 1. One somewhat expects and accepts

this kind of degradation on a twenty-year oldcar, but when a two-year old Lexus shows signsof rust we tend to get a little upset!

Figure 1: Rusted Side Panel

Corrosion accelerated fatigue failures can becatastrophic! A tragic example of that occurredin 1988 when a nineteen-year old Boeing 737lost a major portion of its upper fuselage in fullflight at 24,000 feet. The pilot, somehow,managed to land the plane, as seen in Figure 2.One flight attendant was sucked into the holethat had opened up in the fuselage and wasswept to her death. Many others were injured.

Many fatigue cracks were detected in theremaining fuselage skin lap joints; however, theNational Transportation Safety Boards report


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Figure 2: The Aloha Incident

attributed the incident to the failure of themaintenance program to detect corrosiondamage.

Figure 3: Rivet Hole Crack & Photomicrographs

Figure 3 is an example of a corrosion assistedcrack around a rivet hole. Until the Aloha

Incident almost all inspection of a jet aircraftsskin was done visually. In this paper we willdiscuss better ways to detect corrosionbeforeit becomes a matter of life and death.

Pipeline failures, due to internal and externalcorrosion, have also resulted in both monetaryand human losses.

The photo in figure 4 is the bottom of a pipelinethat has corroded underneath the externalinsulation. If the condition is left undetected,the pipeline could fail at the least opportunemoment, causing loss of property and possibleloss of life.

In this paper we will discuss some of the latestdevelopments in the detection of corrosion. Wewill also describe some of the nondestructiveexamination devices in use at the Department ofEnergys Savannah River Site that could bemade available to other government facilities.

Figure 4: Corrosion Caused by Condensation

SURVEY OF NDE METHODS

A variety of nondestructive examinationmethods have become available that are viablecandidates for the detection of corrosion. Thosethat will be considered are visual, ultrasonic,radiographic, eddy current, electromagneticacoustic transducer scanning, thermographicinspection, and ground penetrating radar.

Being aware that no NDE method producesabsolute discrimination of deleterious anomaliesrequires judicious selection of the test to be usedand a careful selection of inspection points tomaximize the benefits of inspection.

Visual Inspection

As mentioned previously, visual inspection hasbeen and continues to be the primary method todetect corrosion. And, one might argue, eventhe most sophisticated inspection technique

includes the human element. Touching theobject being evaluated and looking at it carefullyis a very important part of the inspectionprocess. Pilots of commercial aircraft make acareful visual inspection of their aircraft prior totakeoff, because they are ultimately responsiblefor the safety of their passengers.

Visual inspection requires good vision, adequatelighting, and knowledge of what to look for.Enhancement of visual inspection can be doneby using low power magnifying glasses, or wheninspecting tubing, the use of boroscopes or video

cameras.

Ultrasonic Inspection

Ultrasonic Testing (UT) methods utilize soundwaves to interrogate an item. They can be usedto measure the thickness or length of an item.UT can also be utilized to detect flaws such ascracks or pitting, detect liquid inside a


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component, measure the length and detectcorrosion of buried anchor rods or interrogateconcrete. Automated ultrasonic inspectionsystems, have been successfully used to detectsubsurface corrosion and cracking in piping,storage tanks, and aircraft components.

Ultrasonic thickness meters have often beenused to check pipelines for corrosion. Whilethese meters can determine wall thickness (andwall thinning) it is very difficult to detectlocalized, internal corrosion with these devices.Ultrasonic thickness mapping of specificallyselected inspection points provides far moreinformation about the condition of a pipingcomponent, tank wall or floor.

Automated ultrasonic inspection systems, and inparticular phased array UT systems, can besuccessfully used to detect subsurface corrosionon piping, tank walls, aircraft lap-joints andmicrocracking around rivets of high speedaircraft.

Figure 5: Phased Array Scan Presentation

Phased array UT systems generate a beam withvarious probe elements pulsing at slightlydifferent times. By precisely controlling thedelays between the probe elements, beams ofvarious angles, focal distance, and focal spotsize can be produced. The illustration shows

how a beam can be focused at an angle and agiven distance by firing the left elements slightlyahead of the corresponding elements on theright. It is possible to change the angle, focaldistance, or focal spot size, simply by changingthe timing to the various elements.

The sectorial scan is a real-time side view

generated from a single inspection point,without any physical motion from the probe.

Radiographic Inspection

Radiographic inspection provides moreinformation about the condition of a component

than any other method; however, radiographicinspection requires the use of dangerous,ionizing radiation. It also requires access to bothsides of the component being inspectedand itis expensive.

Radiographic films have been the primarymethod to capture images of the componentunder investigation; however, there are severalimage recording methods now available. Spacedoes not allow a comprehensive discussion ofthe various methods. One of the newer image

recording devices, referred to as computedradiography, employs the use of photostimulableplates. These plates can be used much the sameas conventional films. Important differences arethat they are reusable, they are more efficient atcollecting data than film, and because the latentimage is digitized the resulting data set has fargreater dynamic range than what can be seenon a film.

Other important methods for capturing radio-graphic images are lens-coupled, charge coupleddevices; direct imaging flat panel devices; linear

arrays; and image intensifiers. All of thesedevices can be configured in programmableautomated scanning systems such as is shownbelow. The collected image data provided byeach of these image collection devices can beenhanced, stored, and retrieved, as can be seenin the data acquired on a 24 inch diameter,insulated pipe that was in service (Figure 5).The data is uniquely quantifiable.

Figure 6: DR of Corroded Pipeline


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Eddy Current Inspection

Eddy current inspection is used quite extensivelyin the aerospace industry. Eddy currentinspection devices aid in the detection of surface(or near surface) anomalies. Eddy current

technology is also an excellent, inexpensive toolused for material sorting and measuring coatingor material thickness. Specialty tubingmanufacturers rely on automated eddy currentinspection devices to test their products. Eddycurrent thickness mapping can be performed todetect corrosion in aluminum aircraft skins.

Electromagnetic Acoustic Transducer (EMAT)

Electromagnetic Acoustic Transducers induceultrasonic waves in metals without the need for acoupling medium. The method is designed forrapid assessment of corrosion in piping even ifthe piping is coated or at temperatures up to500oF. A volumetric interrogation of the fullcircumference of a pipe run is accomplishedwith the EMAT devices astride the top of thepipe, as shown in figure 7. Anomalies that havebeen detected in long runs of piping by thismethod are erosion, pitting, cracking, etc.

Figure 7: EMAT Assembly on Pipe RunThermographic Inspection

Thermographic inspection is commonly referredto as infrared inspection. This inspectionmethod is being successfully used throughoutindustry. Locating hot spot defects in electricalservices has been particularly effective. Otheruses include the determination of process liquid

or catalyst levels in chemical towers and/orcolumns. And boiler tube corrosion has beensuccessfully characterized with a scanningthermal line device that was developed by theLangley Research Center.

Thermographic images are acquired in real-timeand advanced processing provides informationabout coating defects and/or thickness variationsin the coating and sub-surface corrosion spots.

Lawrence Livermore National Laboratory hasdeveloped a dual-band infrared computedtomography system that can search for hiddendefects on bridge decks and airplane fuselages.The dual-band infrared images are acquired asmaps. The data is then processed, revealingcorrosion damage and other surface and sub-surface anomalies. As can be seen in the photo,

the entire system can be mounted and operatedfrom a specially equipped vehicle.

Fig. 8: Dual-Band Infrared Mobile Unit

Ground Penetrating Radar

Recent developments in both hardware andsoftware have both contributed to theavailability of ground penetrating radar systemsthat can provide 3-dimensional informationabout reinforced concrete. In the photo arecomputer generated images that show thelocation and level of rebar in a concrete slab.


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This system was developed by GeophysicalSurvey Systems, Inc.

Figure 9: Severely Degraded Bridge Supports

GPR requires access to only one surface, and isfaster, safer and is less expensive than radio-

graphy. In the photo above the rebar in thebridge supports is seriously degraded. GPR canprovide information concerning rebar that isbelow the surface.

Figure 10: GPR 3D Rebar Image

GPR has been found to be useful in evaluatingexisting structures for continued use,modification or for repair.

WESTINGHOUSE SAVANNAH RIVER

COMPANYS NONDESTRUCTIVEEXAMINATION CAPABILITIES.

The Department of Energys Savannah RiverSite is much like other government agencyfacilities. The facilities are aging, and corrosionhas taken its toll. Fortunately, no one wasinjured when the tower in figure 11 collapsed.

Figure 11: Fallen Tower

In the photo that follows the inventor of SoundAnchor (Bill Hinz) is performing thespecialized ultrasonic examination on the anchorrod of a tower.

Figure 12: UT Anchor Rod at SRS

WSRCs Savannah River Technology Center(SRTC) specialists have developed extensiveexpertise in competencies related to corrosionprevention, detection and mitigation. SRTC hasover 150 engineers focused on materials andreliability systems. SRTC has worked withDOE and other government agencies toevaluated and mitigate corrosion and

deterioration in a variety of materials andenvironments. SRTC provides materialselection, environmental testing, coating andrepair technologies.


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NDE Systems engineers and Materials NDE &Consultation specialists have been called on toprovide non-intrusive, field-deployable NDEmethods that provide the information thatoperations and facilities personnel need toensure that personnel and the environment are

not endangered.

As seen in the photo below, the walls of astorage drum are severely degraded.

Figure 13: Corroded Hazardous Waste Drum

Corroding drums become more serious whenthere is a possibility of releasing radioactivedebris or hazardous waste to the environment.

Corroding storage tanks that contain highlyradioactive waste are also a concern at the

Savannah River Site. The Department ofEnergy has committed itself to turning high levelwaste into glass billets, but, until that task isaccomplished, the storage tanks must bemonitored.

High Level Waste Tank Ultrasonic Testing

Highly radioactive waste is safely stored inunderground tanks. The tanks are 5 to 45 feetbelow grade. Access to these tanks for NDE islimited. SRTC performs remote visual andautomated ultrasonic inspections of the tank

walls through access ports that vary in diameterfrom 5 inches to 8 inches. The access portsprovide entry into a 30 inch wide annular space.

In the figure below is a photo of one of the wallcrawlers that has been developed. The crawlerautomatically positions radiation-hardenedultrasonic transducers, cameras, and lightsources.

Automated ultrasonic inspections are performedon a regular basis to monitor the tank walls forcracking, corrosion, pitting and other forms ofdegradation.

Figure 14: Tank Wall Crawler

The following figure shows UT data of pittingcorrosion that was acquired on a cooling waterline. Dark blue represents base metal thickness.The differing hues represent variations in thethickness of the pipe wall.

Figure 15: UT Data of Cooling Water Line

Filmless Radiographic Imaging

WSRCs NDE System design engineers andspecialists have been recognized internationallyas experts in conceiving, designing, integrating,and deploying filmless (digital) radiographicimaging devices. Filmless radiographic imagingdevices that they have provided are operating atHanford, Washington; Kansas City, Missouri;


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Oak Ridge, Tennessee; and Los Cruces, NewMexico.

Filmless imaging systems that have beendeployed at the Savannah River Site have beenused to interrogate hazardous waste drums,

highly radioactive storage devices, closure weldson pressurized reservoirs, B-25 low level wasteboxes, 3013 assembly inner container lidconfiguration and the closure welds on the outercontainers, and the circumferential welds on4000 drums.

The image of the corroded hazardous wastedrum, shown in figure 13, was acquired with afield deployable filmless imaging setup similarto the one shown in figure 16.

Figure 16: Drum DR Imaging Setup

Most of the filmless imaging systems, developed bythe SRS team, have been cabinet enclosures such asis shown in figure 18. These systems have been usedto acquire radiographic images on everything fromNASA shuttle hardware, to a failed-Plutonium filledstorage container.

A 420 kVp DR cabinet enclosure above and one thatis similar to it are being used to ensure the integrityof 3013 assembly closure welds. Porosity as small as

12 mils in diameter and incomplete fusion wereimaged in some of the pre-production closure welds.

Figure 17: Closure Weld Porosity

Figure 18: 420 kVp DR Cabinet Enclosure

Figure 19: Weld Anomaly in Closure Weld

Figure 20: Photomicrograph of the Weld Anomaly

A field-deployable filmless radiographic imagingsystem that WSRCs DR team will be testing isshown in Figure 21 This imaging device can betransported by land or by air to any emergency site.The device is being evaluated for the Defense ThreatReduction Agency.

Figure 21: Field Deployable DR Imaging Concept

The scintillating screen will have a 34 by 51 inchfield of view. Connecting the scintillating screen tothe charge coupled device camera will be a one of akind, camera bellows. The purpose of the camerabellows is to eliminate light. WSRCs radiationbackground subtraction experience will be useful inthose situations where a radioactive dirty bomb hasbeen transported to a potential target.


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A device similar to that, illustrated in figure 21, couldbe used to inspect piping and vessels for corrosion orblockages.

Conclusions

Corrosion is a fact of life, but things could be worse.Corrosion prevention specialists are doing their partto minimize untimely failures resulting from failedcomponents. And never have there been morenondestructive examination tools available to assistplant engineers in detecting corrosion at early stages.

Early detection and prompt remediation can extendcomponent life, protect the environment, and ensureemployees a safe working environment.

References

www.Corrosion Doctors.org

Boiler Tube Corrosion Characterization with aScanning Thermal Line; K. Elliott Cramer, NASALangley Research Center

www.navalmaterials.com

Dual-Band Infrared Computed Tomography:Searching for Hidden Defects, Ken Dolan;dolan2llnl.gov

Geophysical Survey Systems, Inc., Geophysical.com

Damage Characterization of Corroded 2024-T3Fuselage Lap Joints, Bellinger, Forsyth andKomorowski; [email protected]

Phased Array Ultrasonic Testing, RD-tech.com

The Hidden Threat to all Chill and Cold WaterPiping; www.corrview.com

Application of Infrared and Visual Imaging forInspection and Evaluation of Protective Coatings;Shubinsky, Kwan-Hwa Jan, and Bernecki;www.iti.northwestern.edu
http://www.navalmaterials.com/mailto:[email protected]://www.corrview.com/http://www.iti.northwestern.edu/http://www.iti.northwestern.edu/http://www.corrview.com/mailto:[email protected]://www.navalmaterials.com/

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