TECHNICAL FIELD

This disclosure relates to a device for outputting a signal indicative of the corrosion resistance of a region of an article. The device has particular application for use in the stainless steel fabrication and installation industries and is disclosed in this context. However, it is to be appreciated that the disclosure is not limited to that use. Also disclosed are methods for determining a corrosion resistance indicator of the article region.

BACKGROUND OF THE INVENTION

Stainless steel is manufactured, fabricated and widely used for its corrosion resistance.

Manufacturing standards specify the mechanical properties and chemical composition, but do not directly specify or measure corrosion resistance.

Laboratory instruments are used to determine both the pitting potential and the pitting temperature of stainless steels using laboratory potentiostatic and potentiodynamic techniques. This type of equipment measures a large surface area of the test specimen, it is expensive, time consuming and is required to be done in laboratory type facilities.

The above references to the background art do not constitute an admission that the art forms part of the common general knowledge of a person of ordinary skill in the art. The above references are also not intended to limit the application of the corrosion test device as disclosed herein.

SUMMARY

Disclosed herein is a hand-held device for outputting a signal indicative of the corrosion resistance of a region of an article. The device may comprise a body having a probe able to form an electrochemical cell with the article region, a power source operative to induce a corrosion reaction in the cell, first and second sensors mounted to the body, wherein, during the corrosion reaction in the cell, the first sensor being able to determine a first value relating to a parameter of the article, and the second sensor being able to determine a second value relating to a parameter of the cell, and a signal generator for outputting a signal indicative of the corrosion resistance of the article region responsive to the first and second values.

In some forms, the device further comprises a container mounted to the body for storing a fluid, the container having an applicator for the controllable release of the fluid onto the surface of the article to form the cell with the article region.

In some forms, the applicator is disposed on a portion of the container that projects from an external surface of the body.

In some forms, the power source is operative to modify an electric potential of the cell to induce the corrosion reaction in the cell.

In some forms, the second sensor comprises an ammeter.

In some forms, the device further comprises an return circuit contact pin, wherein the return circuit contact pin is mounted to and projects from the external surface of the body.

In some forms, the ammeter is connected to the return circuit contact pin. In some forms, the probe is immersed in the container such that it contacts the fluid to form the cell with the article region, the fluid and the return circuit contact pin.

In some forms, the probe is in the form of an electrode that is able to form a cathode of the cell during the corrosion reaction.

In some forms, the parameter of the article is temperature. In some forms, the parameter of the cell is current.

In some forms, the first sensor is in the form of a thermometer.

In some forms, the thermometer is an infrared thermometer. In some forms, the thermometer is a thermocouple. In some forms, the thermometer is a resistance thermometer RTD

In some forms, the signal generator is a display for outputting at least one of the first value, the second value and a value indicative of the corrosion resistance.

In some forms, the device further comprises a memory for storing a software program for determining the value indicative of corrosion resistance. In some forms, the device further comprises a database held on the memory, wherein the database is able to store information relating to corrosion resistance.

In some forms, the device further comprises a processor for running the software program, wherein the software program is configured to associate at least one value determined by the device with the information relating to corrosion resistance held in the database to obtain the value indicative of corrosion resistance.

In some forms, the at least one value determined by the device includes at least one of the first value, the second value, the applied potential and a concentration of the applied fluid.

In some forms, the display is configured to output the value indicative of corrosion resistance. In some forms, the signal indicative of the corrosion resistance of the region of an article is a visual representation of the value indicative of corrosion resistance.

In some forms, the value corrosion resistance indicator is in the form of a pitting resistance equivalence value.

In some forms, the database is in the form of at least one lookup table or equation that is held in the memory.

In some forms, the device further comprises a plurality of lights responsive to the second value determined by the second sensor.

In some forms, the power source is able to maintain an electrode potential within 1 millivolts of a pre-set value. In some forms, the power source has a potential range of -1.0 to 1.6 volts. In some forms, the article is a stainless steel. In some forms, the power source is mounted to the body.

In some forms, the fluid includes a predetermined concentration of chloride ions.

Also disclosed herein is a device for testing the corrosion resistance of a metal article. The device may comprise cell generating means to generate an electrochemical cell where a region of the article forms an electrode in that cell, and sensing means to determine a first value relating to a parameter of the article and a second value relating to a parameter of the cell, wherein an indication of the corrosion resistance of the article is established using an estimate of the pitting resistance of the metal in the article region determined from the first and second values.

In some forms, the device is operable to allow the electrochemical cell to be generated in situ on the metal article.

In some forms, the first and second values are able to establish a pitting resistance equivalent number for the metal article region.

In some forms, the electrochemical cell is operative to induce a corrosion reaction in the cell and the sensing means is arranged to determine the first and second values during that corrosion reaction.

In some forms, the parameter of the article is temperature. In some forms, the parameter of the cell is current.

In some forms, the cell generating means comprises a container containing an electrolyte, an applicator to apply the electrolyte to the article region whilst maintaining fluid

communication with the electrolyte in the container, a probe arranged to be immersed in the electrolyte and form a second electrode of the cell and a power source arranged to be connected to the article region and the probe.

Also disclosed herein is a method for determining a corrosion resistance indicator of an article region comprising the steps of, positioning a device adjacent the article region, applying a fluid to the article region using the device, determining the temperature of the article region using the device, and applying an increasing potential with the device to form an electrochemical cell with the article region until a current of the cell determined by the device increases above a value that indicates the corrosion pitting potential of the article

In some forms, the method further comprises comparing a concentration of the applied fluid, the determined temperature, the applied potential with information relating to corrosion resistance held in a database to determine the corrosion resistance indicator.

In some forms, the device performs the step of comparing the concentration of the applied fluid, the determined temperature, and the applied potential with information relating to corrosion resistance held in a database to obtain the corrosion resistance indicator. In some forms, the method further comprises displaying the corrosion resistance indicator.

Also disclosed herein is a method for determining a corrosion resistance indicator of an article region. The method may comprise the steps of, positioning a device adjacent the article region, applying a fluid to the article region using the device, applying a constant potential with the device to form an electrochemical cell, applying an increasing temperature to the article region until a current of the cell determined by the device increases above a value that indicates the corrosion pitting temperature of the article region, recording the critical pitting temperature of the article region, and comparing a concentration of the applied fluid, the critical pitting temperature of the article region and the applied potential with information relating to corrosion resistance held in a database to determine the corrosion resistance indicator.

In some forms, the method further comprises displaying the corrosion resistance indicator.

In some forms, the device performs the step of comparing the concentration of the applied fluid, the determined corrosion pitting temperature of the article region, the applied potential with information relating to corrosion resistance held in a database to determine the corrosion resistance indicator.

In some forms, the applied potential may be 300mV or 600mV.

Also disclosed herein is a method for determining variations of a corrosion resistance indicator of an article comprising the steps of, positioning a device on the article, applying a fluid to the article using the device, applying a constant potential to the article using the device to form an electrochemical cell with the article region, scanning the surface of the article by dragging the device across a surface of the article, and recording variations in the potential, wherein variations in the potential indicate variations of the corrosion resistance of the article. In some forms, the method further comprises displaying the corrosion resistance indicator.

Also disclosed herein is a method for determining a corrosion resistance of an article region comprising the steps of, setting a current on a device, positioning the device on the article region, applying a fluid to the article using the device, maintaining the position of the device for a pre-determined time while applying a constant potential, to form an electrochemical cell with the article region, determining a current of the cell, and determining the corrosion resistance of the article region at the position of the device in dependence on the determined current and the set current.

In some forms, the method further comprises displaying a pass or fail result in dependence on the determined corrosion resistance of the article region. In some forms, the pre-determined time is 10 seconds.

Also disclosed herein is a method for obtaining a pitting resistance equivalence value for a stainless steel article comprising the steps of, positioning a device on the article, forming an electrochemical cell between the device and the article, obtaining article information and cell information with the device, and establishing the pitting resistance equivalence value, wherein the pitting resistance equivalence value is dependent on the article information and cell information.

In some forms, the article information is a temperature of the article and the cell information includes a potential applied by the device, chloride ion concentration of a fluid applied by the device and a current determined by the device. In some forms, the method further comprises the step of displaying the pitting resistance equivalence value on the device.

Also disclosed herein is a method for testing the corrosion resistance of a metal article. The method may comprise generating an electrochemical cell where a region of the article forms an electrode in that cell, and determining a first value relating to a parameter of the article and a second value relating to a parameter of the cell, wherein an indication of the corrosion resistance of the article is established using an estimate of the pitting resistance of the metal in the article region determined from the first and second values.

In some forms, the method further comprises operating a device to allow the electrochemical cell to be generated in situ on the metal article.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments will now be described by way of example only, with reference to the accompanying drawings in which

Figs. 1 illustrates a perspective view of the hand held device;

Fig. 2 illustrates a schematic exploded view of the test instrument shown in Fig. 1 Fig. 3 illustrates a block diagram of the hand held device of Fig.1 that is able to output a signal indicative of the corrosion resistance of the test region of a steel alloy;

Fig. 4 illustrates a schematic diagram of an alternate embodiment of the hand held device, whereby the database and processor is held external to the device;

Fig. 5 illustrates an example look up table prepared for a particular CI ^" concentration; Fig. 6 illustrates a heat affected 316 steel alloy and a graph of the possible variation in

PRE value;

Fig. 7 shows a critical pitting temperature test being performed by a user with the hand held device of Fig. 1; and

Fig. 8 shows a graphical representation of the test range of an instrument that includes 0.1M NaCl, 1M NaCl, 5M NaCl and acidified CI ^" .

DETAILED DESCRIPTION

In the following detailed description, reference is made to accompanying drawings which form a part of the detailed description. The illustrative embodiments described in the detailed description, depicted in the drawings and defined in the claims, are not intended to be limiting. Other embodiments may be utilised and other changes may be made without departing from the spirit or scope of the subject matter presented. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the drawings can be arranged, substituted, combined, separated and designed in a wide variety of different configurations, all of which are contemplated in this disclosure.

The most common form of corrosion occurring on stainless steels is pitting of the surface, caused by chloride ions (salt) in the water. As the temperature is increased, the passive surface breaks down when the Critical Pitting Temperature (CPT) is reached, and pitting corrosion initiates. As corrosion is an electrochemical process, applying a voltage to the surface through the solution at a given temperature can also cause a breakdown of passivity at the Critical Pitting Potential (CPP). This measure is used in laboratory tests of pitting corrosion resistance. The CPP value is different in environments of different chloride levels. The pitting resistance of stainless steels has been found to depend on the Cr, Ni and N alloy contents. An empirical relationship has been determined based on these elements from which the Pitting Resistance Equivalent number (PRE) can be calculated. Stainless steel selection and specification can be based on this PRE value of stainless steel alloys. The factors affecting pitting corrosion resistance are: chloride ion concentration, temperature, corrosion potential and the Cr, Ni and N alloy contents (PRE). By measuring the chloride ion concentration, temperature and corrosion potential, when pitting initiates, the corrosion resistance can be determined. This may be represented as the PRE value. As the surface finish and metallurgical treatment of the metal can also significantly affect the corrosion resistance, the effect of these can be determined using tests.

Test Instrument Fig. 1 shows a perspective view of a hand-held device, in the form of a test instrument 1, for testing a region of an article, in the form of stainless steel. The illustrated instrument is able to provide a simple and portable test that establishes the corrosion resistance of the steel surface. This can be used for quality checks, acceptance criteria and process improvements.

In the illustrated embodiment, the instrument provides a signal indicative of the corrosion resistance of a region of an article through a signal generator. The signal generator is shown in the form of screen 2. In alternate embodiments, the signal generator can be a speaker and the signal can be an audible sound or flashing lights that indicate the corrosion resistance of the stainless steel. The test instrument 1 includes a body, in the form of an outer casing 3. In the illustrated embodiment, the casing 3 has an ergonometric shape such that it can be comfortably gripped by the hand 5 of a user. The test instrument 1 also includes a container

16 (see Fig. 2), an outlet of which projects from an internal cavity of the outer casing 3. The outlet is shown in the form of a nib 7. The instrument 1 also includes a contactpin, in the form of a return circuit contact 9 and a thermometer 11.

Fig. 2 shows a schematic exploded view of the test instrument shown in Fig. 1. The casing 3 has a probe, in the form of electrode 13 that is able to form an electrochemical cell with the test region 15 of the stainless steel. In the illustrated embodiment, the electrode 13 is contained within the internal cavity of the casing 3 and is immersed in a fluid that is stored within the container 16. The test region 15 of the stainless steel can be the area immediately adjacent to where the instrument 1 is positioned by the user. For example, in the situation where two stainless steel pipes have been welded together, the test region is likely to be the region of the weld. The instrument 1 also includes a power source, in the form of a battery 17 that is mounted to the body. The battery 17 is contained within the outer casing 3. The battery 17 is operative to induce a corrosion reaction in the electrochemical cell that is formed by the instrument 1 and the stainless steel.

The instrument 1 includes a first sensor, in the form of thermometer 19. The thermometer is able to determine a first value, in the form of a number value (e.g. degree Celsius) relating to a parameter (e.g. temperature) of the article. The instrument 1 also includes a second sensor, in the form of ammeter 21. During a corrosion reaction in the electrochemical cell, the ammeter 21 is able to determine a second value (e.g. ampere) relating to a parameter (e.g. current) of the cell. In addition, the device includes a contact pin 9 that closes the circuit between the battery 17, electrode 13 and the stainless steel 15 during a corrosion reaction. The contact pin 9 is mounted to and projects from an external surface of the casing 3.

The test instrument is operative to output a signal, in the form of a visual representation, indicative of the corrosion resistance of the article region in response to the determined temperature and current values. The screen 2 is configured to display any combination of the temperature of the stainless steel, the current in the cell, the potential and the value indicative of the corrosion resistance. In one embodiment, the value indicative of the corrosion resistance is the PRE value. Again, PRE is a known measurement of the corrosion resistance of steel alloys. In general, the higher PRE, the more corrosion resistant the steel alloy. Steel alloys with a PRE of above 32 are considered to be seawater (corrosion) resistant.

The container, which is shown in the form of a canister 16, is mounted within the casing 3 for storing a fluid. The canister 16 is in fluid communication with the porous nib 7 for the controllable release of the fluid onto the surface 14 of the stainless steel 15 to form the cell with the article region. The nib 7 projects from an external surface of the casing 3. This enables the nib 7 to be applied to the surface of the stainless steel 15. In an alternate embodiment, the fluid can be located on the surface of stainless steel using a fluid applicator that is separate to the instrument 1.

In one form, the device includes a cell generating means. The cell generating means is in the form of the canister 16, nib 7, the fluid (e.g. an electrolyte), electrode 13, battery 17 and electrical wiring to complete the circuit. In one form, the device includes a sensing means, in the form of thermometer 19 and ammeter 21.

Electrochemical Cell

Referring again to Fig. 2, the electrochemical cell formed by the instrument 1 and the region of the article 15 will now be described in detail. Together, the battery 17, the electrode 13, the fluid 25, the surface of the stainless steel 15 and the contact pin 9 form an electrochemical cell.

The battery 17, applies a potential between the electrode 13 and the stainless steel 15, through the solution 25, which flows through the porous nib 7. A protective chromium oxide layer on the stainless steel provides a high resistance and low current. Upon the application of a potential between the electrode 13 and the stainless steel 1 , the protective chromium layer breaks down and the stainless steel begins to corrode. At this point, a corrosion reaction takes place in the electrochemical cell. According to ohms law (V=IR), when the oxide layer breaks down, the resistance of the stainless steel (including the oxide layer) reduces. When the resistance decreases, the current in the electrochemical cell increases to maintain the voltage. An increase in the current indicates the occurrence of a corrosion reaction in the electrochemical cell.

The battery 17 is operative to modify an electric potential of the cell to induce the corrosion reaction in the cell. For example, the potential can be increased incrementally until the test region of the stainless steel begins to corrode (e.g. the determined current increases significantly). In the illustrated embodiments, the battery 17 is able to maintain an electrode potential within 1 millivolts of a pre-set value and has a potential range of -1.0 to 1.6 volts and an anodic current output range of 1.0 to 10 ⁵ μΑ. The potential-measuring circuit has a high input impedance in of the order of 10 ^{1 1} to 10 ¹⁴ Ohm to minimize current drawn from the system during measurements.

In the detailed embodiments, the electrode 13 is immersed in the canister 16 such that it contacts the fluid to form the cell with the test region of the stainless steel, the fluid and the contact pin 9. As will be evident to the person skilled in the art, the electrode can be located in alternate locations, provided that it is able to contact the fluid to form an electrochemical cell with the stainless steel. The electrode 16 is able to form a cathode of the cell during the corrosion reaction. Preparing the data

This following method details one of many techniques that can be used to establish a data set that can then be used by the test instrument to determine the value indicative of corrosion resistance (e.g. PRE). The disclosed method is used to establish the relationship between chloride iron concentration, temperature, potential and the corrosion resistance indicator (PRE). Further, the disclosed method provides data which can be used either in a lookup table or to establish an equation or algorithm. In the detailed embodiments, the instrument itself uses the test data to determine the PRE. However, as will be appreciated by the skilled addressee, the calculation of the PRE from the data could also be determined by the user (e.g. by using the temperature, current and potential displayed by the device and consulting a lookup table).

For a range of different steel alloys, the critical pitting temperature and the critical pitting potential is determined. The critical pitting potential is the lowest positive potential at which corrosion pits form in a stainless steel alloy oxide. To determine the critical pitting potential, the following experimental steps can be performed:-

Determining Critical Pitting Potential

Step 1 Define PRE values based on alloy composition

Step 2 Select an alloy with a known PRE value (corrosion resistance indicator)

Step 3 Select a constant temperature and CI ^" concentration at which to test the material

Step 4 Form an electrochemical cell with the steel alloy using a probe and fluid

Step 5 Incrementally increase the voltage from OmV whilst reading the current

Determine the critical pitting potential. The critical pitting potential is determined when the current increases above ΙΟΟμΑ/cm ² . If the porous nib has a

Step 6

surface area of 1.5mm square, the "failure" value is triggered when the current exceeds 6μΑ.

Step 7 Take reading of critical pitting potential

Step 8 Repeat for different temperature and CI ^" concentrations

Step 9 Repeat for different alloys The critical pitting temperature is the lowest temperature at which corrosion pits form in a steel alloy oxide. To determine the critical pitting temperature, the following experimental steps can be performed: -

Calculation of PRE by the Test Instrument

The prepared data set can be stored on a memory within the test instrument 1 such that the instrument can determine and output a value indicative of corrosion resistance (e.g. the PRE value). Fig. 3 illustrates a block diagram of a test instrument for outputting a signal indicative of the corrosion resistance of the test region of a steel alloy. The test instrument 1 includes a memory 101 for storing a software program 103 for determining a value indicative of corrosion resistance. The test instrument also includes a processor 105 for running the software program 103. The software program 103 is configured to associate a CI ^" concentration of the applied fluid, the determined temperature, the determined current and the applied potential with information relating to corrosion resistance held in a database 107 to obtain the signal indicative of the corrosion resistance indicator. In the illustrated embodiment, the database 107 is in the form of lookup table that is stored on the internal memory 101 of the test increment. The display screen 2 of the test instrument is configured to output the corrosion resistance indicator value determined by the software program.

In alternate embodiment, the database can be stored on an external database. When the database is held on another device, the processor is able is able to access the database via radio waves and on the internet. In another alternate embodiment, the test instrument can be part of a system, whereby both the database and processor is held on another device. The external computing system may be implemented as a server computing system, or utilising computer resources in the cloud, or any other computer resources. In the embodiment described in relation to Fig. 4, the host system 113 is implemented utilising cloud resources. The system is generally represented by reference numeral 111. The system comprises a host computing system 113, shown in this example as comprising server computers 1 15 which supports computer processes 117. A database 1 19 is implemented by the computing system 113. The host computing system includes the software program for determining the value indicative of corrosion resistance. The computer processes 117 are able to run the software program that is configured to associate a CI ^" concentration of the applied fluid, the determined temperature, the determined current and the applied potential with information relating to corrosion resistance held in the database 119 to obtain the signal indicative of the corrosion resistance indicator. A communications interface 121 is implemented to communicate with other network nodes, via a network (such as the Internet, for example, but not limited thereto).

In this embodiment, user test instruments 123 have access to the system to view the outcomes of the process. In this embodiment, the test instrument 123 is effectively a communication device that communicates (e.g. feeds) data (e.g. data measured using the sensors) to the host computing system 113 and then receives the data (e.g. the signal indicative of corrosion resistance) established by host computing system 113. The data received by the instrument 123 is then able to be displayed on/by the test instrument (e.g. on a display screen, a series of lights, an audible signal etc.). In this embodiment, a plurality of users, each having their own test instrument, may be able to communicate with the host system 1 13 at the same time. Additionally, the data received by the instrument 123 may optionally be sent to another set of system users 125 (e.g. quality assurance devices/people). In this way, the corrosion resistance of the tested environment is able to be tracked live. Optionally, the device/users 125 may also communicate with the host system 1 13 and the test instalments 123. For example, the device/users 125 may send a signal to the user of the test instruments 123 to re-perform a test.

Fig. 5 shows an example look up table prepared for a particular CI ^" concentration. The lookup table 201 includes the y-axis (temperature value 203) and an x-axis (PRE value 205). The data values in the lookup table represent the potential 207. The PRE value 205 is indicative of the corrosion resistance of a steel alloy (e.g. "304 stainless steel" has a PRE value of 18). In alternate embodiments, the determined relationship between temperature, potential and PRE value can form the basis of an equation instead of a lookup table. The use of this lookup table will now be described with reference to the particular tests that can be performed using the test instrument 1.

Critical Pitting Potential Test

The critical pitting potential test is particularly useful when a user needs to accurately determine the corrosion resistance of a stainless steel alloy in situations where the

temperature of the steel alloy is relatively constant (e.g. on-site testing). For example, if two lengths of "316 stainless steel" pipe are welded together on site, the user may be required to test the welded region. The constant temperature test allows for the corrosion resistance of the welded region of the installed stainless steel to be accurately tested onsite (i.e. without having to send the pipe off-site to a laboratory). An example of a heat affected "316 steel alloy" 15 and a graph 301 of the possible variation in PRE value is shown in Fig. 6. Using the data established above for the PRE value, a test of the region of the stainless steel alloy in question can be performed by the following method steps:

Critical Pitting Potential Test

Apply instrument to affected area (i.e. a location on the alloy that has been

Step 1 welded and therefore will likely have a region of lower corrosion resistance relative to the rest of the material);

Step 2 Determine the temperature of the test region;

Incrementally increase the potential to the point at which the current increases

Step 3 dramatically (critical pitting potential of region is reached). The critical pitting temperature is determined when the current increases above ΙΟΟμΑ/cm ² . If the porous nib has a surface area of 1.5mm 2 , the "failure" value is triggered when the current exceeds 6μΑ.

Compare temperature and critical pitting potential to test data establish for that

Step 4

particular CI ^" concentration to determine PRE value;

Step 5 Display the PRE value.

Constant Potential Test

The constant potential test (or 'rapid corrosion test') is particularly useful when a user needs to quickly determine the corrosion resistance in several different locations. The test is especially useful on fabricated items.

Using the established data for the PRE, or by setting the desired PRE value on the test instrument, a test of the region of the steel alloy in question can be performed by following the following method steps:

Constant Potential Test

Apply instrument to affected area (i.e. a location on the alloy that has been

Step 1 welded and therefore will likely have a region of lower corrosion resistance relative to the rest of the material);

Set the critical potential value on the test instrument by selecting the PRE value

Step 2

or by using the PRE value determined in a previous test

Step 3 Hold the potential steady for 10 seconds.

Step 4 Determine the current during the period

Determine if current exceeds the set critical value, an error signal is displayed

Step 5

(fail)

If the current exceeds the set critical value, an error signal is displayed (e.g. fail)

Step 6

- if not, a pass signal is displayed (e.g. pass) Critical Pitting Temperature test

The critical pitting temperature test is particularly useful when a user needs to determine the temperature limit up to which the steel alloy may be safely used in service.

Fig. 7 shows the critical pitting temperature test 401 being performed by a user. Using the data established for PRE, a test of the region of the steel alloy in question can be performed by the following method steps:

Potential Scan (Touch Test)

The potential scan (or 'touch test) is particularly useful when a user does not need to precisely determine the corrosion resistance of a steel alloy. For example, the potential scan can be used as a quick test by a supervisor to verify that the corrosion resistance of particular sections of steel alloy have been measure correctly. Using the established data for PRE, a test of the region of the steel alloy in question can be performed by the following method steps:

Potential Scan

Step 1 Apply instrument to affected area (i.e. a location on the alloy that has been welded and therefore will likely have a region of lower corrosion resistance relative to the rest of the material);

Set a constant potential based on selecting a PRE using a reference test value

Step 2

from a previous test

Either hold the instrument in a single location or drag the instrument across the

Step 3

surface of the steel alloy.

Display the potential such that a user is able to observe changes in voltage to

Step 4

determine areas of decreased corrosion resistance

Alternate Embodiments

In the illustrated embodiments, the signal indicative of the corrosion resistance is a number(s) displayed on a screen. In alternate embodiments, the signal indicative of the corrosion resistance could be audible, a series of lights or a graph displayed on the screen.

In the illustrated embodiments, the value indicative of corrosion resistance is PRE, a known measurement of the corrosion resistance of steel alloys. However, an alternate indicator of corrosion resistance can be used. For example, the test data established could form a scale of 1 to 10, where "1" corresponds to a steel alloy that is highly corrosive and "10" corresponds to a steel alloy with a high corrosion resistance. Alternatively, the steel alloy could be presented on the screen (e.g. "This test region has a corrosion resistance equivalent to 316 stainless steel").

Multiple test instruments can be used, each including a fluid with a different chloride iron concentration. Fig. 8 shows a graphical representation 501 of the test range of an instrument that includes 0.1M NaCl 503, 1M NaCl 505, 5M NaCl 507 and acidified CI 507. In another alternate embodiment, the canister 16 is removably mounted within the casing 3 of the instrument such that canisters can be replaced with new canisters containing fluid with either the same or a different CI ^" concentration.

In the illustrated embodiments, the power source is described as being a DC battery. In alternate embodiments, the power source can be supplied from a general power outlet.

In the claims which follow and in the preceding summary except where the context requires otherwise due to express language or necessary implication, the word "comprising" is used in the sense of "including", that is, the features as above may be associated with further features in various embodiments.

Variations and modifications may be made to the parts previously described without departing from the spirit or ambit of the disclosure.