technical insight
Can mild steel survive where stainless fails?
Lessons from the depths of the Dead Sea
Can mild steel ever outlast stainless steel? It’s a question that challenges conventional engineering wisdom but under the right conditions, such as the ultra-saline, oxygen-starved waters of the Dead Sea, the answer might not be as clear-cut as it seems. This article examines two intriguing technical questions raised during the Sassda Fundamentals of Stainless Steel Course: first, whether Grade 316 stainless steel is appropriate for heating hard water; and second, whether mild steel might, in rare cases, offer greater durability than stainless steel? Grade 316 and Its Application in Hard Water Heating
The Importance of Grade Selection in Stainless Steel Applications Stainless steel is not a single material but a family of more than 200 different grades, each developed for specific operating conditions and environments. Selecting the correct grade is fundamental to achieving reliable performance, optimal corrosion resistance, and long-term cost efficiency. This point was heavily emphasised during a recent session of the Sassda Fundamentals of Stainless Steel Course. Two questions posed during the session highlighted just how critical grade selection can be. The first centred on selecting a suitable material for a vessel designed to heat and hold borehole water - typically high in mineral content - at temperatures above 50°C. The second posed a theoretical, but compelling challenge: is there any situation in which mild steel might outlast stainless steel?
The first scenario described the need for a hot water cylinder operating at atmospheric pressure and intended to heat and store borehole water, which is known for its high hardness and elevated chloride levels. The initial material selection was Grade 316 austenitic stainless steel, a common and reliable choice for chloride-rich environments, thanks to its molybdenum content which enhances resistance to pitting corrosion. From a corrosion protection standpoint, this selection is understandable. The molybdenum in Grade 316 provides improved defence against pitting, particularly when compared to Grade 304. However, corrosion protection involves more than just resistance to pitting. In this particular application, the presence of chlorides, elevated temperatures,
and residual or applied stresses introduces another significant risk: Stress Corrosion Cracking (SCC).
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Issue 2 – 2025
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