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Stainless Steel Types in Pharmaceutical (Detailed Study)

Nowadays material of construction of the product contact part is a very important concern. Generally, stainless Steel is preferred, but again there are so many alloys in SS 304, 316, and 316 L that are very useful and commonly used alloys. Type 304 is a more common alloy of a group of Steel known as Austenitic Stainless Steel.

Components of Stainless steel Grade:

Stainless steel

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 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 SS is similar to type 304 except that type 316 stainless steel has 2 to 4% higher nickel content, 2% less chromium, and has 2 to 3% molybdenum.

The molybdenum gives type 316 improved resistance to pitting corrosion as compared to type SS 304 and slightly improved general corrosion resistance. Type 316 is usually specified for product contact surface, especially heating is involved do to the Superior pitting corrosion resistance.

Both types 304 and 316 SS are susceptible to intergranular corrosion adjacent to the welded area. Austenitic stainless steel is heated From 425 degrees Celsius to 870 degrees Celsius 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 type 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 the distribution of water for injection, clean steam, deionized water, compressed gases to be used in the control environment area, and for product transfer piping.

We are using Stainless steel pipeline only for DM water, water for injection pipeline, but why it is not being applied for Portable water lines also. It may be used for potable water also.

Advantage of Stainless Steel in Pharmaceutical

Due to the polishing surface and material of construction SS are highly resistant to corrosion; thus, it helps to prevent Contamination and is easy to clean and disinfected. 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 SS prevent 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 when it encounters potential damage by machining or chemicals. If the metal is scratched and, therefore, the passive film is disrupted, more oxide will form and recover the exposed surface, protecting it from oxidation corrosion. Though the protective layer is just too thin to be visible, it’s liable for the glossy look of SS.

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