Corrosion Behavior of Stainless steel

Corrosion Behavior of Stainless Steel and High-Alloy Weldments in Aggressive Oxidizing Environments.

Nickel alloy filler metals compensate for the lower corrosion resistance of matching composition stainless steel welds in aggressive environments.

Conclusions

1- Welds made autogenously or with matching-composition filler metals on 2- to 6%-Mo austenitic stainless steels have inherently lower corrosion resistance than the base metal in these low-pH oxidizing environments with chlorides.

2- The lower corrosion resistance is not due to the higher ferrite content of the weld metal. 3- The lower corrosion resistance is due to coring and segregation of molybdenum and to a lesser extent similar segregation of chromium.

4- The use of high-Mo filler metals, such as Alloys 625, C-276 or C-22, overcomes the loss of weld metal corrosion resistance and has become standard for welded fabrication of 4- to 6%- Mo stainless steels.

5- Nickel-based alloys, including clad C-276 and titanium, did not exhibit the marked reduction in corrosion resistance when welded with a matching composition filler metal in these environments. 6- High-alloy clad materials can be produced as welded pipe in much the same manner as welded stainless steel pipe and are good candidates for high-corrosion-resistant pipe.

7- The root pass of groove welds in 6%-Mo pipe may subject to lower corrosion resistance due to insufficient mixing in the molten weld pool. Remedial measures are being investigated.

8- Pickling is very effective in restoring the corrosion resistance of stainless steels after the surface has been degraded by welding, light grinding, stainless steel wire brushing or glass bead blasting. 

9- Matching composition welds in ferritic alloys with 29 to 30% Cr were as corrosion resistant as the base metal, whereas they were not in ferritic alloys with lower (24.5-26%) Cr.

KEY WORDS

TAPPI (Technical Association of the Pulp and Paper Industry)