When connecting pipes of various materials their difference in electrode potential may cause galvanic corrosion and serious damage of pipes, valves and other equipment in the system. Under certain circumstances in environments like water with free ions (like salt sea water), acids or bases, higher temperatures and enough oxygen, the systems deteriorate very fast.
A very common connection in piping systems is copper and low-carbon steel. In connections like this steel corrodes many times faster than steel alone.
A metal with lower electrochemical potential will be the cathode in a connection and will remain unchanged. A metal with higher potential will be the anode and will corrode. The list below indicates the galvanic relationship between some materials commonly used in piping systems.
The metals above will resist the metals below. The greater the distance is between two metals, the greater the speed of corrosion.
|Hastelloy C 4)|
|Stainless Steel (passive)|
|Hastelloy A 4)|
|Stainless Steel 316 1)|
|Stainless Steel 430 2)|
|Stainless Steel 410 3)|
1) Austenitic stainless steel with increased molybdenum content to increase resistance to corrosion compared to other 300 series alloys. Resist scaling at temperatures up to 1600 oF (871 oC). Used in industry, in marine environments and in a wide range of general industrial components.
2) Basic ferritic non-heat treatable stainless steel. Its strengths are in ductility, formability, good corrosion and oxidation resistance, thermal conductivity and finish quality. Used in automotive and architectural trim, heat exchangers and scientific equipment.
3) Martensitic stainless which attain high mechanical properties after heat treatment. Good impact strength, corrosion and scaling resistance up to 1200 oF (649 oC). Used in cutlery, steam and gas turbine blades and buckets, valve components and fasteners.
4) Hastelloy is a trademark for a series of high-strength, nickel based, corrosion resistant alloys. Other components includes molybdenum and chromium. Hastelloy is used in chemical applications. Resistant to pitting, stress-corrosion cracking and to oxidizing atmospheres up to 1900 oF (1037 oC).