A UNS S 32654 , A STAINLESS STEEL FOR CONDENSER TUBES
The new superaustenitic stainless steel UNS S32654 (Avesta Sheffield 654 SMO) is proposed for condenser tubes in desalination and power plants. A number of tests illustrating its corrosion resistance in a variety of chloride containing environments are being reviewed in terms of pitting, crevice corrosion and stress corrosion cracking. Relevant mechanical and physical properties are described. Health hazards and the impact on the environment are discussed as well as the cost benefits of using a stainless steel for this application.
Nickel migration from Cr—Ni stainless steel exposed to potable water
AbstractStudies of nickel migration from Cr–Ni stainless steel exposed to potable water indicate that there is a ‘stagnant water problem’, which is also known to occur with other pipe materials. The nickel levels can reach the EC recommended upper limit within a period of one week; depending on the surface condition and volume to surfacearea ratio. The fact that hardly any chromium is found in the water indicates that the presence of nickel is not attributable to corrosion of Cr–Ni stainless steel pipes but rather to leaching of nickel from the passive layer rich in chromium oxide. The leaching stops after afew weeks, indicating that nickel migration is only a matter of concern during commissioning. Unlike copper and hot dip galvanised steel pipes, stainless steel pipes do not undergo any general corrosion in potable waters. This is also true for waters that are highly acidic (pH 4) or contain strong complex forming species, e.g. cyanides and EDTA. From the point of view of health, therefore, stainless st...
TIME DEPENDENCE OF CATHODIC PROPERTIES OF MATERIALS IN SEAWATER - STAINLESS STEEL, TITANIUM, PLATINUM AND 90/10 CU-NI
This article describes how the cathodic efficiency of stainless steels, titanium, platinum and 90/10 Cu-Ni increases during the first weeks of exposure in natural seawater due to a catalytic action of a microbial slime layer. The increase in cathodic efficiency of stainless steels has been studied for various polarisation potentials, temperatures and flow rates. At temperatures below 30 C and any fixed potential in the region from 200 to -600 mV SCE, the cathodic current density on stainless steels increases strongly after several days or a few weeks of exposure. In the potential range -200 to -1200 mV SCE the lowest current density is found at -1000 mV SCE. In the upper potential region, titanium, platinum and 90/10 Cu-Ni also show an increase in cathodic current density during the same period. The catalytic effect of the biofilm vanishes when the temperature is raised above 30 C. The increased cathodic efficiency leads to a shift in the free corrosion potential, and the initiation and propagation of crevice corrosion are favoured. Current demand for cathodic protection and galvanic corrosion rates on less noble materials in galvanic contact with stainless steels and titanium are increased.