Selecting Corrosion Resistant Stainless Steel Hollow Bar Grades

The primary reason for using stainless steel is its corrosion resistance. However, not all stainless steels are created equal. Choosing the appropriate grade of Corrosion Resistant Stainless Steel Hollow Bar depends critically on the specific service environment. The resistance stems from a passive chromium oxide layer that forms on the surface. Elements like chromium, molybdenum, and nitrogen enhance this resistance.

Different types of corrosion must be considered:

• General Corrosion: Uniform attack across the surface, often in acidic or alkaline solutions.
• Pitting Corrosion: Localized attack forming small pits, common in chloride-containing environments (e.g., seawater). Molybdenum significantly improves resistance.
• Crevice Corrosion: Occurs in tight gaps or under deposits where oxygen levels are depleted, also exacerbated by chlorides.
• Stress Corrosion Cracking (SCC): Cracking caused by the combined action of tensile stress and a corrosive environment, particularly problematic for austenitic grades in hot chloride solutions. Duplex grades offer superior SCC resistance.

Grade 304/304L is suitable for general atmospheric and mild chemical environments. For marine applications, chemical processing, or environments with higher chloride concentrations, grade 316/316L, with its added molybdenum, is typically specified. For highly aggressive conditions, Duplex (e.g., 2205) or Super Duplex (e.g., 2507) grades provide superior performance due to their higher chromium, molybdenum, and nitrogen content.

Corrosion Resistance Comparison (Simplified):

Grade	PREN (Approx.)*	Resistance to Pitting/Crevice Corrosion	Resistance to Chloride SCC
304L	18-20	Moderate	Low
316L	23-28	Good	Moderate
Duplex 2205	30-38	Very Good	High
Super Duplex 2507	>40	Excellent	Very High

*PREN (Pitting Resistance Equivalent Number) = %Cr + 3.3 * %Mo + 16 * %N. Higher values indicate better pitting resistance.