BGCMAP rate of corrosion tester

The BGCMAP corrosion system has been designed to help develop effective maintenance schedules for the electrical power industry.

The system provides a rapid and reliable way of assessing the potential life of steelwork using the Linear Polarisation Resistance (LPR) technique to determine the rate or corrosion.

Powered by rechargeable batteries, the system integrates GPS technology to provide an accurate location, date and time stamp for every test result.

The BGCMAP system glossary has been designed specifically for the power line industry and can be classified in terms of structure, component, line, segment, circuit and street. The user is also able to enter details of the inspector as well as soil and weather conditions.

The unit will automatically apply a current to the structure and determine Ecorr, from which the operator can then choose the best fit line to measure Rp.

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BGCMAP rate of corrosion tester: Frequently asked questions

Q: What is a linear polarisation resistance test?

A: A linear polarisation resistance (LPR) test is a quick corrosion rate monitoring method and can give an indication of the corrosion resistance of materials in their in-situ environment. The measured polarisation resistance is used to determine the corrosion rate of the material using the Stern-Geary equation.

Q: How is linear polarisation resistance measured?

A: The free corrosion potential (ECorr) is first measured between the buried structure and surrounding materials with a half-cell. A current is applied in increments to the circuit through an electrode spike and the changes in electrical potential then recorded around the free potential through the half-cell. The resulting linear polarisation resistance curve is used to derive the polarisation resistance from the best-fit line gradient.

Q: What is the polarisation resistance?

A: Polarisation resistance (Rp) can be defined as the resistance (Ohms) of the test specimen to oxidation during the application of an external potential. The rate of corrosion is directly related to the Rp and hence used to identify potential corrosion risks

Q: What is corrosion current?

A: By assuming certain constants, it is possible to convert the polarisation resistance Rp to a Corrosion current ICorr in mA, which can be used with an assumed affected surface area to determine loss of section/year at the measured rate of corrosion. Given the number of assumptions made these values should be used with caution.

Q: How does the LPR measurement system work?

A: The BGCMAP instrument uses a half-cell, electrode spike and clamp to make the electrochemical connection to the buried steel component to be tested. Once connected to the component the measurement takes approximately 15 seconds. It is very quick.

Q: How should the readings taken be used to assess corrosion?

A: The LPR measurement does not actually determine the corrosion present. It measures the rate of corrosion that is occurring at the time of the test. For this reason, the LPR method is best utilised as a comparative measure of the risk of corrosion being present and to highlight test components most at risk for further investigation.

Q: What are the major types of corrosion?

A: The two major forms of corrosion that are likely to affect buried structures such as lighting columns or transmission tower foundation and anchors, are uniform corrosion and pitting corrosion. Pitting corrosion is localized corrosion at a point where surface protection may be failing and uniform corrosion is more or less uniformly distributed over the surface.


Benefits of the BGCMAP corrosion system:

  • On-site measurement of full LPR curve, ECorr and polarisation resistance
  • Integrated GPS provides location date and time stamp for every test result
  • Transmission line terminology
  • Storage for over 700 results
  • Battery operated, rugged unit for use in remote locations
  • Lightweight and easy to transport
  • User friendly Windows based software for reporting
  • Complete testing package available

All of our equipment is supplied fully calibrated to UK national standards.

BGCMAP system specifications  

Rugged site logger with waterproof connectors
Daylight viewable screen
Tactile large keys for operating with gloves
Low power with long battery life
Flash memory for instant start up and power down
On site LPR measurement
GPS tagged test data

Keypad Sealed colour coded and full alphanumeric keypad, tactile and audio feedback
Operating temperature  0 to +50°C
Screen Monochrome LCD transflective with backlight
Contrast keypad adjustable
Display area 122mm x 77mm
Protective anti-reflective glass
Connectors Uniquely configured waterproof lemo type
Acquisition 2 channel, 16 bit acquisition at 10Khz sample rate
Pre-trigger on both channels
Data transfer USB-PC cable
Storage 700+ results, including full LPR curve, ECorr, Rp with full header information including site, structure, line, segment, weather, soil condition, date, time, latitude and longitude
Voltage range ECorr +/- 20mV
Current range Auto
GPS Trimble Lassen SQ module with integral embedded antenna
Protocols are TSIP and NMEA 0183
Accuracy of the GPS is - 
Horizontal: Altitude: 
Power Battery: 1.2V NiMH rechargeable AA cells
Auto power off and battery indicator
Battery life 8 hours + operation on full charge
Charge time Approx 6 hours
Charging External wall plug-in charger for 100/110/250VAC inputs (trickle charge)
External cigar plug-in charger for 12VDC inputs (fast charge)
Dimensions L 218mm x W 187mm x D 55mm
Weight 1.35Kg
Half-cell sensor
Type Commercial CuCuSO4 half-cell fitted with porous ceramic plug and supplied ready filled with crystals

The BGCMAP software operates under Windows XP and follows all of the usual file handling protocols. Files are downloaded from the site unit and are automatically entered into a report table.

From the table each file can be viewed independently and site data reviewed. The 'best fit' slope can be chosen to determine the polarisation resistance.

Corrosion of a steel element embedded in the ground is an electrochemical process. It acts as a galvanic cell in a similar way to a battery producing an electric current. This current can be measured on the surface as an electric field and compared with an electrode at a standard potential.

The BGCMAP operates by applying a current (ΔΙ) and recording the change in electric potential (ΔΕ) that occurs between the half-cell and the corroding sample. These values are plotted against each other. For small values around the free corrosion potential (Ecorr), the plot is assumed to be linear, the slope of which is the polarisation resistance (Rp).

Application to transmission tower legs

Carrying out the test on transmission tower legs is easy and rapid. The electrode spike is driven into the ground within 1m of the component, to a depth of at least 200mm.

The BGCMAP unit is connected to the component and the electrode using heavy duty steel clips. Any surface coating at the point of contact is removed beforehand. The copper / copper sulphate half-cell is then inserted firmly into the ground, in a small hole excavated alongside the component being tested.

The test is carried out automatically by the BGCMAP, which applies a current and records the voltage. The GPS co-ordinates and the date and time of the test are also recorded.

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