Title

CORROSION RESISTANCE OF DUPLEX STAINLESS STEELS IN THERMAL DESALINATION PLANTS

Authors

S. Jacques, J. Peultier, J-C. Gagnepain and P. Soulignac, INDUSTEEL, ArcelorMittal group

Source

CORROSION 2008, March 16 - 20, 2008 , New Orleans LA

Copyright

2008. NACE International

Keywords

duplex stainless steel, pitting corrosion resistance, crevice corrosion resistance and thermal desalination processes

Language

English

Preview

ABSTRACT

The number of countries, which suffer from a shortage of fresh water resources, is increasing continuously. For this reason, the number of desalination projects (production of fresh water from sea water) is booming. In the past, carbon steel, clad steels, copper-nickel alloys, or austenitic stainless steel grades such as 316L were the primary materials used for the walls of thermal process evaporation cells. More recently the duplex grades UNS S32304 and UNS S32205 have been selected for this application. This paper provides some of the technical reasons, which brought about this change in the choice of materials selected. Initially, the results of an extensive corrosion study, performed in a representative environment for evaporation cells and including both duplex and austenitic grades, are presented and discussed. Then a joint corrosion testing program conducted in cooperation with a well established desalination plant designer and run under actual plant conditions is outlined. The results of these field tests led to the development of a new concept for evaporation cells based on utilizing duplex stainless steels.

INTRODUCTION

The number of countries, which suffer from a shortage of fresh water resources, is increasing continuously due to population increases. The total global water stock is 97.5% salt or brackish and only 2.5% fresh water. Approximately 70% of this global fresh water stock is locked up in polar icecaps and a major part of the remaining 30% lies in remote underground aquifers. Indeed, only a miniscule fraction of fresh water (less than 1% of total fresh water or 0.007% of the total global water stock) that is available in rivers, lakes and reservoirs is readily accessible for direct human use. Fresh water is of vital importance and is needed for different purposes such as potable water or agriculture. Desalination is thus one of mankind's earliest forms of separating fresh water from a salt-water solution. Desalination [1] may be defined as: "the art of producing fresh potable water from a saline supply at a reasonable cost with reasonable reliability". There are different techniques to desalt water and for production of industrial or high quantity potable water, distillation and reverse osmosis are the most widely used [2-7]. The thermal processes have been developed primarily in countries where the desalination plant can be linked to a power plant, which can act as a low temperature heat source. The major thermal processes are: Multi Stage Flash distillation (MSF) and Multi Effect Distillation (MED) [4,8-12]. In this paper, the focus is on the MED process, which is described below. This process can generate aggressive conditions in some parts of the system, which may cause corrosion problems. As a consequence, highly corrosion resistant stainless steels must be selected in order to insure the continuous operation of the system. Therefore the selection of materials must be done with a complete understanding of the process parameters.

MULTI EFFECT DISTILLATION PROCESS (MED)

Description

The Multi Effect Distillation (MED) installation consists of several consecutive cells (or effects) operating at decreasing levels of pressure and temperature from the first cell (hot, 145.4F / 63C) to the last one (cold, about 104F / 40C) [2-4] (FIGURE 1).

Number of Pages

17