Connecting pipes of different materials may cause galvanic corrosion and serious damage.
When connecting pipes of various materials the difference in electrode potential may cause galvanic corrosion and serious damage on 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, systems deteriorates very fast.
It is common to connect copper and low-carbon steel and in piping systems like this the steel corrodes many times faster than steel would do alone.
In a connection the metal with the lower electro-chemical potential will be the cathode and remain unchanged. The metal with the higher potential will be the anode and will corrode. The list below indicates galvanic relationships between commonly used materials in piping systems.
- metals above resists 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).