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GC-Compass®: A Software Tool for Galvanic Corrosion Prediction and Materials Galvanic Compatibility Assessment  


Version 9.18

 

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Features and Component of GC-Compass

GC-Compass is the only device and OS indepedent software tool on the market for the prediction of galvanic corrosion and assessment of materials galvanic compatibility. Designers, engineers, architects, consultants, maintenance and inspection personnel can quickly assess and quantify the impact of galvanic coupling of dissimilar metals on the remaining life of their components or systems anytime, anywhere, on any device running any OS without the need to install or download anything.

 

GC-Compass consists of two modules:

  • Metals and Alloys module is used for for galvanic corrosion prediction and galvanic compatibility assessment of metals, alloys, metal matrix and carbon fibre composites.

  • Intermetallics module for the prediction of galvanic corrosion and the risk of intermetallics-induced pitting in aluminium alloys used in engineering, microelectronics and semiconductor applications.

Overview and Application Examples of GC-Compass for Metals and Alloys

This module is used for the prediction of galvanic corrosion and assessment of materials galvanic compatibility for a given galvanic couple in a chosen application. Figures below show the screen shots of GC-Compass.

 

Figure 1 Overview of GC-Compass: Metals and Alloys Module

 

Users of GC-Compass start by selecting the dissimilar metal couple from the dropdown list. The database has over 200 galvanic couples and is updated regularly with more couples added to the list. If you cannot find the couple of your interest in the list, do let us know through the Contact Us link and we will conduct the necessary tests to generate the required data for inclusion in the software.

 

Figure 2 Over 200 Galvanic Couples Included in the Software

 

After selecting the galvanic couple, the next step is to select the environment relevant to your application. The dropdown list in Figure 3 below has 7 options from seawater to industrial atmosphere, representing the natural environments. If your process fluids are not listed in the dropdown menu, you should choose one of the waters that closely matches the chloride level in your process fluids.

 

Figure 3 Seven Types of Environments Included in the Software

 

The next step is to enter the temperature of the environment. Temperature is a critical factor that influences the rate of corrosion. Some galvanic couples such as zinc-steel and aluminium-steel will reverse the polarity at certain temperatures, meaning the usual anodes (zinc and aluminium) have become the cathodes with respect to steel when the temperature exceeds certain threshhold value, as shown in Figure 4 below.

 

Figure 4 Polarity Reversal for Zinc in Zn-Carbon Steel Couple

 

GC-Compass models the effects of temperature and the cathode to anode area ratio on the corrosion rate of the anodic membr of the couple. The outputs from the software include:

  • the predicted corrosion rate of the anode metal in mm per year, mm/y.

  • the remaining life of the component assembly based on the corrosion rate of the anodic membeer of the galvanic couple.

  • the galvanic compatibility class based on the quantitative evaluation of the acceleration factor due to galvanic effect. Class I means the materials are galvanically compatible with less significant increase in corrosion of the anode metal; Class II means borderline condition where galvanic corrosion of the anode metal is expected but the acceleration in corrosion is moderate; Class III means the materials are not galvanically compatible in the selected enviornment. Severe galvanic effect is expected to cause rapid failure of the anode metal.

 

Figure 5 The Effect of Temperature and Cathode to Anode Area Ratio

 

GC-Compass is not only powerful for the prediction of galvanic corrosion and assessment of galvanic compatibility of metals and alloys, it is also equally powerful for the prediction of the corrosion rate of a single metal when it is not galvanically coupled to another metal. This can be easily done by setting the "cathode to anode area ratio" to zero, then the anode metal in the selected couple is effectively corroding independently without the influence of galvanic effect. Now you can change the temperature or the enviornment and see the predicted remaining life of the anode metal without the influence of galvanic corrosion.

 

Service Life Prediction for Fasteners

GC-Compass can be a particularly powerful tool for predicting the performance or service life of fasteners. For example, the SS316 fasteners used on AA6061 plates exposed to seawater at 60oC can be predicted using the "effective thickness of anode". Assuming that the fastening assembly will fail when the hole in the AA6061 plates loses 0.35 mm thickness (or the diameter of the hole increases by 0.70 mm),  GC-Compass predcits that the SS316-AA6061 assembly exposed to seawater at 60oC would fail in just over 5 months (Figure 6) below. Numerous fastener configurations (materials both feerous and non-ferrous, with metallic coatings such as cadmium, nickel, zinc and galvanizing) exposed to marine and industrial environments can be assessed and evaluated at the design stage before service failures occur in the fields.

 

Figure 6 Service Life Prediction for Fasteners

 

Service Life Predition for Process Piping in Semiconductor Manufacturing

In semiconductor manufacturing, the process cooling water is frequently contaminated with copper ions, which will deposit on AA6061 piping surface and induce pitting corrosion in AA6061. The temperature of process cooling water is about 90oC and the pipe wall thickness is 2.85 mm. Tap water in GC-Compass closely matches the chloride level in the process cooling water. With these basic information (Figure 7), GC-Compass predicts that the piping would leak in about 2.5 years after operation due to the galvanic effect of AA6061 and copper in the form of pitting corrosion!

 

Figure 7 Service Life Prediction for Process Piping in Semiconductor Manufacturing

 

Service Life Prediction for Structures in Marine and Seawater Services

AA6061 plate and carbon steel structural members were used for the construction of a vessel for seawater services. The effective cathode to anode area ratio is 11.04. The vessel leaked just over 2 years after commencing operation. The galvanic compatibility between AA6061 and carbon steel predicted by GC-Compassis is Class III, which means the two materials are not compatible in the seawater environment, and the time-to-leak predicted by GC-Compass is 2.462 years (Figure 8).

 

Figure 8 Service Life Prediction for Structures in Marine and Seawater Services

 

Service Life Prediction for Carbon Steel Storage Tank with Stainless Steel 304 Clad Bottom

In a major expansion program, a plant installed several hundred large storage tanks. Most of the older tanks were made of ordinary carbon steel and completely coated on the inside with a baked phenolic paint. The solutions in the tanks were only mildly corrosive to steel but contamination of the product was a major consideration. The coating on the floor was damaged because of mechanical abuse and some maintenance was required. The tops and sides were made of steel, with the sides welded to the stainless steel (304) clad bottoms. The steel was coated with the same phenolic paint, with the coating covering only a small portion of the stainless steel below the weld. A few months after start-up of the new plant, the tanks started failing because of perforation of the side walls. It was observed that most of the holes were located within a 2-inch band above the weld. This is a classic galvanic corrosion case involving the question of which metal to coat -carbon steel or stainless steel. In GC-Compass (Figure 9), we use tap water to represent the mildly corrosive solutions in the tank. The uncoated stainless steel tank bottom and the coating breaks/defects/holidays on the coated carbon steel ensues a cathode to anode area ratio of at least 300. GC-Compass predict that galvanic corrosion would perforate the wall thickness in 0.224 years (2.688 months)!

 

Figure 9 Galvanic Corrosion in Carbon Steel Storage Tank with SS304 Clad Bottom

 

Service Life Prediction of a Aluminium Casing of a Water Heater

A hospital needed an emergency power supply in case of mains failure, so a diesel engine was provided. To ensure that the diesel would cut in immediately the power failed, it was kept warm by means of a water heater with an aluminium casing. After a few months in operation, the 8 mm thick aluminium casing was penetrated causing the water to leak out. Inspection showed that a copper heating element had been used. Copper ions deposited at the 12 o'clock position by convection and caused extremely rapid pitting. In GC-Compass (Figure 10), the Al-Cu galvanic couple is selected and it predicted that the 8 mm thick Al casing would be perforated in 0.292 years (3.5 months).

 

Figure 10 Pitting in Aluminium Casing

 

The powerful applications of GC-Compass are truely unlimited in enginnering design, materials compatibility evaluation, trouble-shooting process-related issues and failure analysis.

 

Overview of GC-Compass for Intermetallics

Intermetallics, their size and distribution in the matrix of aluminium alloys, are critical factors influencing their mechanical strength and their corrosion resistance properties. Figure 10 shows an overview of the GC-Compass module for Intermetallics.

 

Figure 11 Overview of GC-Compass for Intermetallics in Aluminium Alloys

 

A dozen of intermetallics commonly found in aluminium alloys are available for selection in GC-Compass. If you cannot find the intermetallics of your interest in the list, do let us know through the Contact Us link and we will conduct the necessary tests to generate the required data for inclusion in the software.

 

Figure 12 Common Intermetallics in Aluminium Alloys in GC-Compass

 

Users simply enter the conductivity and the operating temperature of the process water/fluids, GC-Compass takes care of the rest.

 

Figure 13 Electrolyte in GC-Compass for Intermetallics in Aluminium Alloys

 

Outputs from GC-Compass includes the following:

  • Predicted potential difference (at 25oC) with respect to the alloy matrix (α-Al). The greater the potential difference, the greater the galvanic effect between the IM particles and the matrix.

  • The galvanic position of the selected intermetallic with respect to the alloy matrix. The intermetallic can be anodic to the matrix or cathodic to the matrix, depending on the composition of the intermetallic.

  • The intermetallic-induced pitting rate in nano-meter per hour (nm/h), and micro-meter per year (µm/y).

  • The expected pit morphorlogy. For intermetallics anodic to the matrix, the intermetallics themselves will be preferentially dissolved, leading to the formation of deep pits in the alloy matrix (see photo below). For intermetallics cathodic to the matrix, the intermetallics act as cathodes in the corrosion process and they are not subject to corrosion. However, the matrix is the anode in the corrosion process and corrodes around the isolated IM particles, leading to the formation of circumferential pits with the IM particles remain in the center (see photo above). Eventually, the IM particles will fall out of the pit holes.

 

Figure 14 Prediction Outputs in GC-Compass for Intermetallics in Aluminium Alloys

 

WebCorr can customize GC-Compass for your specific process fluids and alloys used in any industry from general engineering to wafer fabrication.


GC-Compass, giving you the right directions in Galvanic Corrosion Prediction and Assessment

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