Steel Grades and Specifications Explained (Part 3): Tensile/Yield Strength

Steel grades - image of rolled steel coil

In our most recent post in this series, Steel Grades and Specifications Explained (Part 2), we took a look at steel categories and classifications, as well as a further look at sub-categories of carbon steel. Most pallet rack today is made of carbon steel, but not all carbon steels products are the same. There are different steel grades resulting in different tensile strength and yields that can affect the quality and strength (and ultimately the safety) of the finished product. Here’s what you need to know.

Tensile Strength and Yield Strength

Tensile strength and yield strength are important measures of a material’s ability to perform in an application, and the measurements are widely used when describing the properties of metals and alloys.

The main difference between yield strength and tensile strength is that yield strength is the minimum stress under which a material deforms permanently, whereas tensile strength describes the maximum stress that a material can handle before breaking.

A metal’s yield strength and ultimate tensile strength values are typically expressed in the U.S. as pounds per square inch (psi), or kilo-pounds per square inch (kpsi).

Minimum Tensile Strength and Yield Strength of Pallet Rack

Different grades of steel will have different tensile and yield strengths. It’s generally accepted and recommended by engineers that steel used for pallet rack have a minimum yield strength  of 50,000 psi. Most US manufacturers use steel rated from 50,000 to 55,000 psi (All Next Level FlexRack™ has a minimum of 55,000 psi.) Much of the steel coming out of Asia will be less, often as low as 40,000 psi. How can you know what you are getting? Ask for a mill certificate.

Mill Certificates Explained

The mill certificate is a mill-issued document that provides the end-user of the raw material verification that the material received matches the requirements of their order. The mill certificate goes by a variety of  names, such as Mill Sheet, Mill Test Certificate (MTC), Mill Test Report (MTR), Certified Mill Test Report (CMTR), or Metallurgical Test Report. These reports are also used to maintain traceability of the material from its inception to its inclusion in a finished part. All mill certificates have a ”heat number” and all accompanying paper work, and in many cases markings on the raw material itself, must match the heat number on the certificate.

Stay tuned for our last post in this four-part series on steel grades and specifications – we’ll be looking at the different surface finishes available for steel.

Next Level uses a high yield strength carbon steel. Our frames start at 55,000 PSI, and our beams start at a minimum 60,000 Kpsi yield steel.  We can produce mill certificates for every piece of coil that we purchase.

Photo Credit: Mikko J. Putkonen, Public Domaine

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