CORROSION RESISTANCE OF NICKEL ALLOYS AND SUPER AUSTENITIC STAINLESS STEEL WELD CLADDING AS A FUNCTION OF DILUTION

摘要

Overlay welding of carbon and low-alloy steels with corrosion resistant alloys is a widely-used process for corrosion protection today. It allows generating a compact and tightly bonded layer of corrosion resistant alloy on a framework of less expensive material (e.g. carbon steel) which would not fulfil the corrosion resistance. Furthermore it gives the possibility of cladding more complex geometrical forms (e.g. fittings). Overlay welding is therefore increasingly applied in different segments like the Oil & Gas, Chemical Process Industry or Energy Industry. During the overlay welding process a dilution of the weld cladding with the base metal will occur. To save costs, fabricators try to keep the overlay layer as thin as possible, which may result in a high content of base material in the clad. Changing the composition of the clad material will change the corrosion resistance also. For the present paper, different Nickel alloys as Alloy 625 (UNS N06625), Alloy 59 (UNS N06059), Alloy 22 (UNS N06022), Alloy 825 (UNS N08825) and one Special Stainless Steel (Alloy 31 UNS N08031) are overlay welded in 1 to 3 layers on carbon steel. The dilution is measured by EDX-technique and is also shown as an element concentration diagram in correlation of the layer thickness. Furthermore results of pitting corrosion in an immersion test with "Green Death" solution will be discussed.