Chloride-Bearing Cooling Water and
the Stress-Corrosion Cracking of
Austenitic Stainless Steel
DONALD WARREN , Research Associate
Engineering Research Laboratory , Engineering Department
E.I. du Pont de Nemours & Co.
Wilmington, Delaware
INTRODUCTION
, Stress-corrosion cracking due to chlorides is the biggest single problem
facing industrial users of austenitic stainless steel today. This problem must
be considered whenever heated austenitic stainless steel equipment is operated
with chloride-bearing cooling water.
Stress-corrosion cracking involves a combination of three factors (1): a
susceptible material, a tensile stress, either residual or applied, and a specific corrosive environment. In most cases, neither the stress nor the corrosive attack, acting individually, would be sufficient to cause failure of the
material. However, the combination of the two can lead to severe cracking
of a brittle nature.
The phenomenon of stress-corrosion cracking has certain unique characteristics (2). First, it generally occurs in metallic alloys rather than in pure
metals. Secondly, for a given alloy the corrosive environments which can
cause stress-corrosion cracking are quite specific to that alloy. For example,
copper-base alloys are subject to stress-corrosion cracking in ammonia vapors,
while mild steel can undergo cracking in nitrate or caustic solutions (1). For
austenitic stainless steels, the "Achilles' heel" happens to be aqueous
chloride environments.
Stress-corrosion cracking is a particularly insidious form of material
failure because it often occurs without prior warning. There may be little or
no evidence of corrosive attack, with perhaps only slight pitting or very light
intergranular attack.
The susceptibility of austenitic stainless steels to stress-corrosion cracking
is rather unexpected in light of their unique properties. These iron-base alloys
contain roughly 18-30 per cent Cr, eight-20 per cent Ni, and up to 0.25 per
cent C. They are quite ductile, easily formed, and readily welded. Their
application in the chemical industry is based primarily on their excellent corrosion resistance. Yet, in spite of their high ductility and excellent corrosion
resistance, the austenitic stainless steels are subject to brittle cracking when
exposed to chloride environments under certain conditions.
The stress-corrosion cracking of austenitic stainless steels due to chlorides
was recognized and reported (3) as early as 1939. During the last decade, this
phenomenon has been the subject of intensive research both in this country and
abroad. Because of the numerous published papers, the reader is referred to a
recent and complete bibliography (4).
OUTLINE OF INVESTIGATION
This paper will deal with the stress-corrosion cracking of cfustenitic stainless steel in cooling-water systems of the once-through variety rather than
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