Nowadays, the material of construction for the manufacturing equipment part is a very important concern. Manufacturing equipment is Generally made of stainless Steel, but again there are so many alloys in SS like; 304, 316, and 316 L. these are very useful and commonly used alloys. Type 304 is a more common alloy group of Steel known as Austenitic Stainless Steel.
Components of Stainless steel Grade:
These allow are generally characterized as containing 18% chromium and 8% Nickel, being non-magnetic and non-hardenable.
Difference between SS 304 and 316L:
Type 304 is resistant to attack by nitric acid but it may be attacked by sulfuric acid and hydrochloric acid.
Type 304 is a good general-purpose alloy for pharmaceutical applications where pitting corrosion is not a problem.
Type 316 is similar to type 304 except that, type 316 stainless steel has 2 to 4% higher nickel content, 2% less chromium, and 2 to 3% molybdenum.
The molybdenum gives resistance to pitting corrosion as compared to SS 304 and slightly improves general corrosion resistance. Type 316 is usually specified for product contact surface, especially heating is involved due to the Superior pitting corrosion resistance.
Both types 304 and 316 are susceptible to intergranular corrosion adjacent to the welded area. Austenitic stainless steel is heated From 425°C to 870°C and cooled slowly as adjacent to a weld. The carbon tends to form chromium carbides which precipitate at the grain boundaries, resulting in reduced resistance to intergranular corrosion.
How to Prevent Intergranular corrosion?
Alloy Stainless steel 304 L and 316 L were developed to avoid this problem by reducing the alloy carbon content to below 0.03%, compared to 0.08% and 0.1% for types 304 and 316, respectively.
Use of SS grade:
The low-carbon alloy of either 304 or 316 should be used when the piping system requires welding and when annealing after welding is impracticable. Type 316 L piping is typically used for water for injection, clean steam, deionized water, compressed gas distribution to be used in the control environment area, and product transfer piping.
Pharmaceutical companies are using Stainless steel pipelines only for DM water, and water for injection, but why it is not being applied for Portable water lines also? It may be used for potable water.
Advantages of Stainless Steel in Pharmaceutical
Due to the polishing surface and MOC of SS being highly resistant to corrosion; thus, it helps to prevent Contamination, easy to clean and disinfect. Due to the smooth polishing surface, it doesn’t encourage bacteria growth. Stainless Steel also adds an advantage to ventilation systems by preventing the growth of molds.
How Stainless steel Prevents Contamination and corrosion (Mechanism)
Stainless Steel doesn’t release contaminants because, the chromium content of the steel combines with oxygen within the atmosphere to make an invisible film of chrome-containing oxide, called the passive layer.
The chromium oxide layer protects SS while encountering potential damage by machining and chemicals. If the metal is scratched, therefore the passive film becomes disrupted, resulting in more oxide will form and recover the exposed surface, that will helps it from protecting from oxidation corrosion. Though the protective layer is just too thin to be visible, it’s liable for the glossy look of SS.