Optical and visual testing - Boroscopy and Endoscopy


Main objective

Optical and visual testing have been widely known in the diagnostics of civil engineer structures, since methods are easily available and do not require large expenditures and effort in application. In literature both methods are assigned mostly in category of non-destructive testing, however sometimes they fall into destructive category, since in some particular cases there is a need of inducing minor damages in case of difficult to reach areas .

However, historically, when developed technology and equipment was not existing - usefulness of this methods was highly limited and not accurate. Especially due to high subjectivity and no possibility of recording hardcopy documentation. Final analysis of the inspected damages or structures was highly dependent on the operator., quality of tested object and optical instrument.

Nowadays there are available very advanced optical technologies and as a result borescope’s and endoscope’s popularity has increased in diagnostics of bridge or tunnels as a routine operational equipment. Currently assessment of the structure behaviour is also affected by the operator, however the quality of imaging is much more developed, which simplifies the task.

Despite its advantages and disadvantages – both boroscopy and endoscopy cannot be used as a sole method of verification and should be coupled with other non-destructive or destructive surveying technologies in order to receive accurate answer on the structural behaviour and state of the infrastructure.


Functioning mode

Borescopes and endoscopes are devices used to inspect hard-to-reach, dark places. It can be the inside of the profile or the engine compartment, elements of the vehicle suspension or an air conditioning system. They allow the observation of very complex devices without the need to disassemble. In case of civil engineering structures inspection this is also a main advantage of the equipment allowing to test difficult to reach areas with no source of light or at night. Endoscopes/videoscopes are a more advanced types of the borescope that has video and still image recording capabilities. Main components of the borescope and endoscope are objective lens system, relay lens system, eyepiece. The eyepiece determines the magnification. At the end of the tool there are objective lens which works similarly to a camera lens. First image of the object is created at the back of the lens and relay lens reform it along the length of the borescope or endoscope. The last set of lenses produce the final image, which can be seen through the eyepiece. The magnification of the lens and eyepiece are determined by the manufacturer and is referred to magnification at a specific distance and mathematically it is a logarithmic function. Modern equipment allows to have a complete video processing system (closed-circuit television) with computerized video enhancement and high-resolution display. Other important elements are – video output terminal (in case of endoscopes), insertion tube, handle, remote control (e.g. brightness/center button, live/gain button, measurement joystick or freeze button) .



  • rigid/half rigid borescopes – usually in diameter 4 to 19 mm with different types of light sources (UV,VIS,LED); extendable versions available on the market as well – in that case the diameter can vary between 9,5 mm up to 44 mm,
  • flexible borescopes – diameter range from 3 mm to 10 mm,
  • micro borescopes – usually in diameter of 1 mm to 3,5 mm.
  • periscopes – for use in underwater or high/low pressure conditions.


  • rigid endoscopes
  • flexible endoscopes

The parameters are usually similar for borescopes and endoscopes, in both cases there is USB interface and built-in memory of, for instance, 64Mb. The cable of the borescope or endoscope has usually length of 1 m.

Technical specifications, availability and prices of different types of borescopes and endoscopes can be found on the websites of the manufacturers as well with the operational manuals .

Process/event to be detected or monitored

By means of borescopes and endoscopes it is possible to detect and photograph abnormal sections on the structural elements of the bridge or tunnel with cracks or deformations. Moreover it is possible to detect areas affected by different types of corrosion or chemical attack. Typical defects observed on the concrete structures can be found in Guidebook on non-destructive testing of concrete structures .

Physical quantity to be measured (e.g. actions, displacements, deformations, dynamic structural properties, material properties including mechanical, electrical and chemical properties, relative displacements of the two sides of a crack, etc.).

No physical quantity is directly measured in case of boroscopy or endoscopy, however as stated in section 1.3.3. it is possible to detect visible effects of the degradation processes occurring on structural elements of the bridge or tunnel.

Induced damage to the structure during the measurement

Inspection of concrete often require using a drill hole for inserting the structural inspection endoscope, this method causes minor damage to the structure. Despite this, in most cases, both boroscopy and endoscopy are non-destructive to the structure.

General characteristics

Measurement type (static or dynamic, local or global, short-term or continuous, etc.)

Inspection with borescopes and endoscopes is static and performed locally in a short-term conditions.

Measurement range

Not applicable.

Measurement accuracy

Depends on the magnification of the lens and adjustment of the camera to the inspected element or area.

Background (evolution through the years)

Borescopes and endoscopes were primarily used in inspection of the pipes and tubing. Lenox Instrument Company, was a pioneer in the development of borescopes for a various applications around the world. First borescope for turbine rotor inspections was found in 1921. Lenox Instrument Company supplied borescopes for inspecting hard to reach, often dark, locations. Applications included power turbines, oil refinery piping, gas mains, soft drink tanks, and many other remote locations. After 1944 Lenox improved its borescope with radiation resistant optics and a swivel-joint eyepiece, which permitted the operator to work from any angle. This newer instrument was also capable of considerable bending to snake through the tubes in the reactor. Lenox supplied a total of three borescopes with radiation resistant optics; they were the first optical instruments to be used in a nuclear environment. .

Endoscopes have mainly experienced four stages of development, from the initial rigid tube endoscope, semi-flexed endoscope to fiber endoscope, and now electronic endoscope. With the continuous improvement of the endoscope structure, the image quality is also undergoing a qualitative leap. The original endoscope used candle light as the light source. Later, Edison invented the electric light bulb, and the endoscope was changed to the light bulb as the light source. Today’s endoscopes mainly use optical fibers or LED lights as light sources. Shenzhen Coantec Technology focuses on the research of endoscopes. It has been carefully thinking about the choice of light source and the improvement of image quality .


General points of attention and requirements

Design criteria and requirements for the design of the survey

Before the survey with use of the borescope or the endoscope there should be few issues considered when performing an inspection. In the first place – what kind of defects could be present and in what elements of the bridge or tunnel structure. Secondly – what would be the nature of the defect and if the tested area is reachable by the operator without any risk. Regarding the equipment itself care should be taken while use – LCD monitor should not be subjected to impact, pressure or scratching.

Procedures for defining layout of the survey

Details on general rules of the survey with visual testing can be found in norm EN 13018:2016 - Non-destructive testing - Visual testing - General principles. Standard specify the general principles and requirements for direct and remote testing and can be used as a guide, however it applies to the determination of a product with specified requirements, so attention is required, and should not be treated as an only source of information.

Design constraints (e.g. related to the measurement principles of the monitoring technologies)

Most important issue that shall be considered is the access to the tested element and if inspection will not induce the risk for operator’s safety.

Sensibility of measurements to environmental conditions.

Measurement with borescope and endoscope is not influenced by environmental conditions.


Procedures for calibration, initialisation, and post-installation verification

Adjustment of the equipment should be performed depending on the objective of the inspection. The inspector should be trained and qualified. Details on the equipment adjustment can be found in manufacturers manual

Procedures for estimating the component of measurement uncertainty resulting from calibration of the data acquisition system (calibration uncertainty)

Not applicable.

Requirements for data acquisition depending on measured physical quantity (e.g. based on the variation rate)

Not applicable.


Requirements and recommendations for maintenance during operation (in case of continuous maintenance)

Not applicable for continuous maintenance. Details on the equipment use recommendations can be found in manufacturers manuals .

Criteria for the successive surveying campaigns for updating the sensors. The campaigns include: (i) Georeferenced frame, i.e. the global location on the bridge; (ii) Alignment of sensor data, relative alignment of the data collected in a surveying; (iii) Multi-temporal registration to previous campaigns; and (iv) Diagnostics.

Not applicable.


Report should include:

  • identification of the equipment used,
  • inspected area, element,
  • scope of research,
  • date of survey,
  • photos and/or videos adequately labelled and described with date/hour/description of the place of inspection and surrounding conditions.

Lifespan of the technology and required maintenance (if applied for continuous monitoring)

Boroscopy and endoscopy are not used in continuous monitoring.

Interpretation and validation of results

Expected output (Format, e.g. numbers in a .txt file)

Photos and videos collected on the memory card as jpg files etc.

Interpretation (e.g. each number of the file symbolizes the acceleration of a degree of freedom in the bridge)

Visual evaluation based on the photos and videos recorded.


Specific methods used for validation of results depending on the technique

No specific guidelines available.

Quantification of the error

Not applicable.

Quantitative or qualitative evaluation

Boroscopy and endoscopy are used in qualitative evaluation.

Detection accuracy

Primarily depends on the resolution of camera and experience of the operator.


  • Recording directly on the memory card.
  • Small diameter of the camera to pass through the tiniest holes.
  • Various photo resolution settings and low cost.
  • The durability guaranteed by stainless steel construction of the device.


Experience of the operator required to properly understand observed issues.

Possibility of automatising the measurements

Live video inspections can now be viewed in real time from a computer, tablet or smartphone across the room or around the world.


The main barrier in the survey includes the access to the tested areas for the operator, which can be limited.

Existing standards

EN 13018:2016 - Non-destructive testing - Visual testing - General principles.

ACI 201.1R, ACI 207.3R, ACI 224.1R, ACI 362R.


Relevant knowledge fields

  • Construction diagnostics,
  • Construction appraisal,
  • Design studies of facilities subjected to dynamic loads,
  • Technical expertise regarding assessment of impact of vibrations on buildings,
  • Analysis of the reliability of shell structures.

Performance Indicators

  • cracks,
  • holes,
  • deformation,
  • obstruction/impeding,
  • rupture.

Type of structure

  • bridges,
  • tunnels,
  • walls,
  • buildings,
  • viaducts,
  • marine hydrotechnical structures,
  • lining of tunnels and mining shafts,
  • foundations.

Spatial scales addressed (whole structure vs specific asset elements)

Boroscopy and Endoscopy can be used to inspect specific elements of bridges or tunnels which are primarily subjected to corrosion risk and mechanical damages and accessible for the operator.


  • concrete,
  • steel,
  • composites,
  • polymers,
  • ceramics.

Available knowledge

Reference projects

No reference projects.


Examples of application of borescopes and endoscopes in real case studies:

  • Assessment of the technical condition of selected buildings on the premises of PGE GiEK S.A. Turów Power Plant Branch, Poland;
  • Assessment of the technical condition along with material tests of the structural elements of the Electrolytic Baths Hall on the area of KGHM Polska Miedź S.A., Poland;
  • Technical expertise of the steel supporting structure of the hall with a cubature in Łazy, Poland.

Borescope Inspection Training and Certification


  • AXIO MET. (2021, 12 10). Borescopes — inspection in harsh conditions. Retrieved from AXIO MET Instruments with a digital Soul: https://axiomet.eu/pl/en/page/1127/borescopes-inspection-in-harsh-conditions-en/
  • D. Mężyk, P. S. (2016). Wprowadzenie do zaawansowanych technik pomiarowych 3D stosowanych w wideoboroskopowych zdalnych badaniach wizualnych. Przegląd Spawalnictwa - Welding Technology Review vol 88 No 10.
  • Davis, A. (1998). Nondestructive Test Methods for Evaluation of Concrete in Structures/ACI 228.2R-98. American Concrete Institute.
  • International Atomic Energy Agency. (2002). Guidebook on non-destructive testing of concrete structures. Training Course No.17. Vienna: IAEA.
  • Lenox Instrument Company. (2021, 12 11). History of borescopes. Retrieved from Lenox Instruments: https://www.lenoxinst.com/About_History_2_Borescopes.html
  • Mężyk, D. (2010, 3). Zastosowanie endoskopii przemysłowej w procesie badań wizualnych jako metody diagnostyki obiektów przemysłowych. Dozór Techniczny.
  • Mix, P. E. (2005). Introduction to Nondestructive Testing - A Training Guide . New Jersey: John Wiley & Sons,Inc. .
  • Olympus. (2021, 12 10). Olympus Instructions - Industrial Endoscope. Retrieved from Olympus Support Downloads : https://www.olympus-ims.com/en/.downloads/download/?file=285218824&fl=en_US&inline
  • PGE. (2021, 12 10). PGE Polska Grupa Energetyczna SA. Retrieved from https://elturow.pgegiek.pl/strona-glowna
  • The Nippon Communications Foundation. (2021, 12 10). Olympus Endoscopes: The Inside Story. Retrieved from https://www.nippon.com/en/features/c00513/