Criterion 6.2.4 Incompatible Materials

Criterion text:
Incompatible materials shall be isolated or treated to prevent degradation to the extent that their function could be significantly impaired under in-service conditions.

Comments:
The use of components has been reviewed by SRCC during the system design review phase. Components have been selected by the manufacturer and approved by SRCC to ensure that the components are compatible with all other approved system components and materials.

The installer should have a general understanding of the compatibility of materials. Installers are at times confronted with unique situations in the field that require this knowledge. This is especially true when plumbing water heaters or using couplings and connectors.

Corrosion caused by the contact between dissimilar metals is called galvanic corrosion. Such corrosion usually results in an accelerated rate of attack on only one of several dissimilar metals. In the language of the corrosion expert, the protected material - the one that remains virtually unattacked - is called the cathode. The material that is attacked is called the anode.

Metals can be listed in a galvanic series that is useful in predicting which metals are acceptable for use in contact with one another and which materials are likely to be corroded. The following (Figure 1) is a simplified galvanic table that can be used as a reference source.

The coupling of two metals from different groups will result in accelerated corrosion of the metal higher in the series. The farther apart the metals are in the series, the greater the galvanic corrosion tendency. Material groups marked with an asterisk (*) have no strong tendency to produce galvanic action and from a practical standpoint are safe to use in contact with one another.

Figure 1

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