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An Introduction to CSA – Class H

on January 19, 2017

You’ve probably heard about CSA – Class H material at some point but might not be familiar with it. Today, I’d like to reintroduce you to Class H.

What is CSA G40.21 50W/350W Class H?

As defined in CSA G40.20, Class H Hollow Structural Sections (HSS) are produced by one of two methods: (A) seamless or furnace-butt welding (continuous welding) or automatic electric-welding process, and hot-formed to final shape; or (B) automatic electric-welding process producing a continuous weld, and cold-formed to final shape; subsequently stress relieved by heating to a temperature of 450°C (850°F) or higher; followed by cooling in air. At Atlas Tube, we produce our Class H HSS by heat-treating cold formed HSS using method B.

How do we produce Class H material?

Material produced for CSA G40.21 50W/350 W Class H follows the same manufacturing process as CSA G40.21 50W/350W Class C (an example of the process can be seen here in this video). After production, the material is moved to a 201km (71’) long rail car that can be fed into a furnace. Before it reaches the furnace, nine thermocouples are positioned at strategic locations throughout the load. Each thermocouple monitors the temperature of the product throughout the furnace cycle to ensure the temperature is staying even throughout the load.

Once the temperature is stable at 476°C (890°F), it is held there for 30 minutes. Then, it is brought back to the ambient temperature, tested and re-tagged. Once complete, the material is ready for shipment.

Next month we will look at several of the benefits Class H has. If you are interested in more information, please download our flyer or send me an email:

Disclaimer: It is important to note that CSA Class H is part of the Canadian specification only and is not associated with ASTM A500 in the United States.