One landscape architectural design trend I have noticed over the past several years has been the innovative integration of stainless steel in the exterior built environment. From retaining walls to linear water features, to coping and cladding treatments, stainless steel has repeatedly been the material of choice. Whether selected for its durability, stark contrast to other more “natural” landscape materials, or sheer aesthetic properties, I seem to be specifiying more of it than ever. For this reason, I thought it might be helpful to outline some of the characteristics of stainless steel types (alloys) when considering its’ use in the landscape.

The specific alloy of stainless steel should be chosen to match the intended use of the metal. For simplicity sake, I would say there are roughly eleven standard architectural stainless steel alloys out of the close to sixty alloys recognized by the American Iron and Steel institute. Of these eleven alloys, consisting of the “200 Series”, “300 Series” and “400 Series”, the “300 Series” make up the majority and are predominatly the ones specified for landscape, site and marine applications.

Narrowed down further, Types 301, 302, 304 and 316 are the alloys commonly used for architectural stainless steel applications; Type 301 being the least corrosive resistant and Type 316 being the most. In general, Type 304 is usually my choice, given its excellent corrosion resistance, good workability, and good for welding – low carbon content. If the stainless steel application happens to be within an exterior urban or coastal environment where chloride and sulfur deposits might predominate making pitting corrosion a concern, then Type 316 is the choice.

A word about low carbon content alloys. If welding of stainless steel is required, a modified alloy type, designated by the letter “L” following the alloy number may be used, such as 316L. A condition is created when chromium carbides form at the site of the weld, stripping the protective chromium layer and allowing localized corrosion to occur. The “L” designation stands for low carbon alloy stainless steel.  Designating a low carbon stainless steel alloy reduces the formation of chromium carbide. The one caveat however is that the lower carbon versions of the 304 and 316 stainless steel alloys have a reduced yield stress, therefore the lower strength trade off must be considered when using the low carbon alloys.

Thanks for reading and stop back in January when my next Specification News topic will address stainless steel finishes, their number system designation, description and uses.