Corrosion is the destructive attack of a material by reaction with its environment. Corrosion control is achieved by recognising and understanding corrosion mechanisms. Following the research of the English scientist Michael Faraday it has been understood that most corrosion is electrochemical in nature. Since corrosion is an electrochemical process, it follows that electrochemical techniques and electrochemical instrumentation can be used to study the corrosion process. Electrochemical techniques are well understood by corrosion scientists and it is a rare corrosion laboratory that does not have at least one ACM Instrument.
Electrochemical techniques are popular because they are fast, accurate and versatile. Much faster than weight loss coupons, accurate even to the lowest corrosion rates and versatile enough to cope with any test in laboratory or field it is easy to see why electrochemical instruments are the bedrock of corrosion research. A number of electrochemical techniques have been developed specifically for corrosion measurement. Among these techniques are Linear Polarisation Resistance, Cyclic Polarisation, Potentiostatic testing, Galvanodynamic sweeps, and Critical Pitting Temperature tests. All these tests are very straightforward to employ in a corrosion laboratory or in the field.
Corrosion scientists also make extensive use of AC Impedance (sometimes called Electrochemical Impedance Spectroscopy). This has been well researched over the last 30 years and proves a very useful technique, allowing measurements to be taken in unlikely electrolytes as well as showing details of the corrosion mechanism hidden from DC tests. Here at ACM we also understand physics as well as corrosion and know our sampling theory. To get the ultimate precision and speed along with the vital 50 or 60 Hz rejection you need to sample the waves as fast as possible. Sampling slowly and building up the waves allows the phenomena of Faradaic Rectification to occur, spoiling the result. So we use fast accurate analysers and crunch the numbers with an on-board Digital Signal processor in real time for superb AC results.
Of particular interest to ACM is Current and Voltage Noise (sometimes called Electrochemical Noise). Both senior directors of ACM were involved with front line research at post-doctoral level during the early days of Current and Voltage Noise. Scientists have applied C & V Noise to the measurement of uniform corrosion rate, localised corrosion, and inhibitor evaluation. The exceptional feature of this technique is that the sample is not driven to any unnatural potentials, thus maintaining the surface condition of the metal.
For the newcomer to corrosion we recommend the Corrosion and Protection Centre, [UMIST]. Established in 1972 it offers an excellent Masters course in corrosion as well as numerous short course options. One of the world's first dedicated corrosion centres it encourages specialists from different academic disciplines to cross their traditional boundaries and work in relevant areas of corrosion and protection.
ACM Instruments has the world's widest range of electrochemical instrumentation for corrosion measurement, we make over fifty different instruments and one purpose of this web page is to help guide the new user to the correct instrument for the job. One example of ACM's dedication and experience is our attitude to grounded samples, we love them. Since our foundation in 1985 we have always made our potentiostats electrically isolated from ground, so flow rigs, pipelines, bund walls, and Blackpool Tower prove no problem for your fully floating optically isolated ACM Instrument.
All of our computer controlled instruments use a standard RS232 port as the interface (or use a USB to RS232 adapter). This allows any Windows PC the world over to be used as the controller, be it portable, desk top or miniature single board. No messing about opening up obsolete 'ISA slot' computers with a screwdriver to plug in a little PCB card with nothing to show for your investment.
ACM Instruments products for the Corrosion Scientist are described below, starting with our first choice instruments and finishing with some very unusual models:
The Gill AC is the preferred choice of hundreds of corrosion labs the world over. This single channel instrument boasts all the capabilities of its larger brothers and represents very good value for money. If more than one Gill AC is owned they may be combined in the Sequencer to form a fast simultaneous system with up to 32 Gill ACs running in parallel and, as a bonus, the additional ones cost even less than the first!
The Gill 8 and the Gill 12 represent our flagship laboratory models. Offering Two Amps of output and 8 or 12 sequential channels they will take pride of place in any corrosion laboratory. All instruments come with a full compliment of AC and DC software including such different tests as Harmonic Analysis and Galvanodynamic, no need for a long options list like a Mercedes!
The Field Machine is the best instrument in the world for corrosion testing in the field, here at ACM we are very proud of this instrument. Housed in a rugged waterproof case, protecting the electronics and portable PC, this instrument will perform all the corrosion tests, both AC and DC, on multiple channels whilst running under its own considerable battery power. Once you own a Field Machine you will wonder how you ever managed without one!
The Weld Tester is a very serious piece of equipment. Like many ACM products it is unique. Able to test up to 5 parts of any couple simultaneously with AC and DC tests it allows the response of each segment to be determined. The multi-element cell could be a sectioned weld or a mixed metal system. Up to 12 separate cells can be tested, ideal for checking weld sensitisation in relation to real operational fluids or even mixed metal heat exchangers. The Weld Tester does not just test welds!
Now for some of the other, more specialised, instruments:
The GalvoGill 12 avoids the problems generated by multiplex units when performing long term tests. Twelve Zero Resistance Ammeters (ZRAs) constantly monitor twelve pairs of electrodes to record the current flow with time. There are no switching currents as in a multiplexed system. Each pair may also have a reference electrode which is fully buffered and recorded.
The Pot 16 has 16 potentiostats built in, each at a fixed range i.e. not changed through the software. This allows very long tests of electrodes under potentiostatic control to be performed in complete certainty that the set potential will not be changed. The current flowing is recorded with time. Ideal for testing cathodic disbonding, CP systems, and sensitisation with no multiplexer switching spikes.
The Gal 16 has 16 galvanostats built in, each at a fixed range i.e. not changed through the software. This allows very long tests of electrodes under galvanostatic control to be performed in complete certainty that the set current will not be changed. Current and potential are recorded with time. Ideal for testing cathodic disbonding, CP systems, and sensitisation with no multiplexer switching spikes.
The Anode 16 is used to determine the potential and current carrying capacity of alloys used for Cathodic Protection. It provides an easily used and reliable method of screening batches of anodes to ensure performance consistency for batch to batch.
The Zed 16 features 16 zero resistance ammeters and is used to measure current flowing between two working electrodes for each channel. Each channel can also have a high impedance reference electrode input for measuring the potential of the couple.
The Parallel 30 LPR comprises thirty channels, two or three electrode. Each channel has a dedicated potentiostat and a four range ZRA for the determination of corrosion rate using LPR. The cells can be two or three electrode, when in three electrode mode the software allows for the LPR test to be performed at the rest potential. A very cost effective multichannel corrosion tester.
The Isolated 20 allows for individual pairs of working electrodes, with reference electrode, to be used in a common electrolyte without stray galvanic coupling between the pairs. The galvanic couples are maintained by 20 individual ZRAs, each galvanically isolated from the others unlike the GalvoGill 12 in which each pair is referenced to instrument ground (never mains ground in one of our instruments).
The Bubble Test is software for use with a Gill 12 or any collection of Gill ACs. Designed to test oilfield inhibitors it produces perfect reports with graphs showing percentage inhibition and charts. The philosophy behind this software was simplicity and ease of use, allowing any untrained operator to produce very technical reports on the performance of inhibited systems.
The Critical Pitting Temperature test offers a standard ASTM test with full control of the heating cycle and potentiostatic settings. The ability to perform this test is built into every Gill AC, and may be made operational on request.
The Speedy 9 was originally built by us for biological research. Each of its 9 channels has a dedicated pair of 24 bit ADCs to measure current and voltage and 8 decades of count resistors. The result is a device that can measure current and voltage at 60 readings per second for each channel; 1,080 twenty-four bit readings per second. This high speed may be applied during a cyclic sweep, at a fixed potential, or during galvanic measurements.
If you have reached here and still have not decided which instrument you would like perhaps you need one of our Bespoke Instruments. These are customised to your exact requirements and, because they usually perform a single specialised test, they often cost less than a fully equipped Gill AC, Gill 8, or Field Machine. Just contact ACM with your requirements and we will quote price and delivery within 24 hours. Finally, all ACM Instruments are now covered by our great new 2 year warranty for your peace of mind.
See Application Notes for more information on AC Impedance, Critical Pitting Temperature, inhibitors, welds, ER, Current and Voltage Noise and LPR techniques plus many more.
Isolated 20
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