load on tube

To echo what others have replied to postings on various engineering basics, if you need to ask these sorts of questions, you shouldn't be designing something safety-critical like scaffolding. You need to study mechanical engineering properly.

For a start, you're dealing with compressive loads. It's mainly the elastic modulus that determines the buckling load and hence the safe working load, but you haven't mentioned elastic modulus in your list of properties.

Cheers......Codey

You just said "I am working as a product development engineer."

I doubt it if you are an engineering graduate, since all of your queries can be answered by an engineering student in his junior years taking up strength of materials.

You ask for steps to calculate strength, but I think perhaps you don't really mean strength. Are you instead looking for maximum safe load?

yes sir.

OK. So, do you only produce the tubing or do you also produce the scaffolding?

This sounds like a homework problem for a sophomore level strength of materials or introduction to structural analysis I course. As an engineer you should already know very well how to perform such calculations.