round tubing vs pipe question

[americanmusc1e]

I didn't know exactly where to post this, but I have a question on round tubing.

Is there a major strength difference between schedule 40 (or schedule 80 for that matter) pipe and round tubing? and will it matter in my case?

I'm needing to build a few things for my truck including a new engine crossmember and eventually some bumpers and whatever. I seem to recall reading somewhere that you are not supposed to use "water pipe" in any structural application, but I have access to a large amount of free schedule 40 pipe. Some of it is galvanized, but I have welded on galvanized stuff before. I am aware that the galvanizing needs to be removed around the weld and its important to keep adequate ventilation. Assuming that my welds are good and my creations are properly engineered, can I use the schedule 40 or should I look into buying what I need?