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Stainless Steel 201 vs 304 vs 316: The Hidden Truth Behind the Shine

2025-09-10

When you scroll through shiny floor drain photos online, they all look identical—until the first brown spot appears.

Behind every mirror finish hides a three-digit code: 201, 304 or 316.

Know the numbers, or pay for rust.

What the codes really mean
  • 201: 17 % Cr, 4.5 % Ni, 6 % Mn – “budget blend” with manganese replacing expensive nickel.
  • 304: 18 % Cr, 8 % Ni – the global workhorse.
  • 316: 16 % Cr, 10 % Ni, 2 % Mo – marine-grade thanks to molybdenum.
Rust in real life

Independent salt-spray data (ASTM B117, public archive) show first red rust at:

  • 201: 24 h
  • 304: 168 h
  • 316: 720 h
The magnetic trick

201 is strongly magnetic because of its Mn-rich structure.

Carry a pocket magnet on site; if the top plate clings like a fridge sticker, you know the supplier sneaked in 201 even when you paid for 304.

When is 201 “okay”?

Indoor, low-humidity, zero-chloride, rent-to-sell projects where the warranty ends at hand-over. For every wet room that sees deodorant, sweat or beach sand, insist on 304 minimum.

Where Each Steel Makes Sense
  • 201: Budget hotel in desert climates, light-duty residential drains that will be replaced every 5–7 years.
  • 304: 90 % of the world’s taps, drains and kitchen sinks. Safe up to 200 ppm chlorides (most city tap water sits below 50 ppm).
  • 316: Indoor pools, beach-front condos, cruise ships, any place where chloride > 500 ppm or cleaning chemicals contain bleach.

So, are you ready to pick your stainless steel without looking back?