Apart from this information, if you are interested in sending a specific enquiry, please fill in this questionnaire and send it.

In humid environments, should I use AISI 304 or AISI 316?

  Susana Adamez Collado

As a reference to determine the convenience of being exposed to salt/marine environments, in general it could be said that up to 100 ppm* AISI 304 (EN 1.4301) could be used and up to 1,000 ppm, chlorides may be in contact with stainless steel AISI 316 (EN 1.4401), without pitting corrosion risk. 

*Approximately 1 ppm is 1 mg/l

Regardless of using one option or the other, the design of the element exposed to moistening and subsequent drying, for example, stairs, handrails, etc., must facilitate water drainage. The formation of chloride deposits on the element surface after drying, should be absolutely avoided. The concentration of these deposits can increase over 1,000 ppm, attacking the zone with corrosion.

The most sensitive zones to these effects are:

HAZ or Heat-affected zones:
In both sides of the weld zone, the microstructure of the material has been altered. Chromium carbide could form and concentrate in the grain boundaries. When  chromium carbide concentrates in a zone, means that there is weakening of chromium content in other, exposing the zone to possible corrosive agents. To decrease those effects stainless steel with low carbon content
should be used, (“L” type, AISI 304L, AISI 316L).

Mechanical joining zones:
If different metals are joined galvanic corrosion could appear. For example, you must be careful when installing stainless steel profiles using non-stainless fasteners. If possible, it would be better to use the same grade of stainless steel than the profiles, 
not only because of galvanic corrosion but also because of general corrosion may appear for the presence of humidity/humidity+chlorides in the environment.

The aim is to prevent galvanic corrosion caused by fixing the stainless steel profiles to another less noble material.

Therefore, oxygen is reduced in the interstices created in the joints increasing the risk of crevice corrosion, if critical values of Cl- are reached. 

In those cases, the design of the element is a key factor to decrease the effects avoiding the gaps or spaces filled with deposits.

As a result of this enquiry, we would suggest the election of the most homogeneous finish possible, to avoid any formation of deposits.

Whatever avoids the formation of deposits, benefits stainless steel.

Finally the adequate maintenance of the element is crucial because favours that external contaminants, such as humidity or chloride deposits, iron contaminants or any other aggressive chemical agent, that exceptionally could have adhered to stainless steel surface are eliminated.

We would like to insist in the fact that maintenance and design of an element is essential to extend the life of the material.