load for steel pipe

That's a very long and slender span. I fear that it will sag (so all the skillets will slide to the center and pull the pipe ends out of their end sockets in the 4"x4" vertical beams), and/or then maybe the pipe also buckles in bending abruptly, in both cases dropping everything on the floor.
That pipe probably needs at least one center support, maybe more.
This needs a four-to-one safety factor, assuming that the pans are packed as closely as possible (regardless of current intent).
You will have to do some computations:
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Joe Gwinn

That's a very long and slender span. I fear that it will sag (so all the skillets will slide to the center and pull the pipe ends out of their end sockets in the 4"x4" vertical beams), and/or then maybe the pipe also buckles in bending abruptly, in both cases dropping everything on the floor.
That pipe probably needs at least one center support, maybe more.
This needs a four-to-one safety factor, assuming that the pans are packed as closely as possible (regardless of current intent).
You will have to do some computations:
.
Joe Gwinn
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The standards for guardrails are somewhat relevant to this.

"Handrails and guards shall be designed to resist a linear load of 50 pounds per linear foot (plf) (0.73 kN/m) in accordance with Section 4.5.1 of ASCE 7."
"Handrails and guards shall be designed to resist a concentrated load of 200 pounds (0.89 kN) in accordance with Section 4.5.1 of ASCE 7. "

"(2) For pipe railings: posts, top rails, and intermediate railings shall be at least one and one-half inches nominal diameter (schedule 40 pipe) with posts spaced not more than 8 feet (2.4 m) apart on centers."
While that doesn't directly answer the question, it suggests that some readily available size of water pipe should be an acceptable answer, and worth pursuing more closely by defining the load and calculating the second moment of area, maximum stress and deflection of several sizes.

The Modulus of Elasticity is assumed to be the same for all steel, regardless of its hardness. 1 ksi is 1000 psi, pounds per square inch, lbf is pounds of force rather than of weight. Stress is the tension or compression force per square inch in the metal.

No problem. 1" gas pipe is about 1-1/4" diameter and quite sturdy. 2-300 pound, distributed static load is nothing.

pipe (see link from Hope Depot below). It will be supported on either end b y 4"x4"x5' wood supports. I will probably be hanging about 40 cast iron ski llets which may weigh about 200-300 lbs. Will this pipe support this weight ? Thank you all for your messages and your input!

Thank you all for your messages and your input!
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Unfortunately free structural engineering help can be dangerous like free legal or medical advice. I'd like someone to check my calculations too, but I can't complain if they don't.

This nominal 1inch pipe - if you told me its actual dimension - two of three of inner dia, wall thk., outer diameter - or what "Schedule" of 1inch pipe so I can look it up - I'd run the Euler-Bernoulli beam calculation on it. You could do Euler-Bernoulli - the familiar beam calc. yourself
Second Moment of Area v Section modulus v Section Moment capacity v Load-bearing capacity
You could also get the expected deflection - which can be had when you know the Second Moment of Area.
Rich Smith

what a nerd fest. It's black gas pipe as used in the US. Does it have guaranteed structural properties? no. Will a 5 foot piece hold up skillets arranged like clothing in a closet on hangers? yes, it will.

You can do this very quickly when you are used to it. I have some "functions" which run in my text editor. I've even done an analysis to completion in chalk on my welding bench at work, just recalling the formulae and doing the arithmetic.
Then you can have really beneficial applications. eg. I really really wanted to make sure all my colleagues were alright on this job.
So - maybe, maybe not - take your own pick
Rich S

Not an answer to your question but why do you want to do this? 5' = 60" so you're allowing 1.5" per skillet. I have 6 cast iron skillets that vary in depth from 1.75" to 3.25" in depth. No way to fit 40 of even the shallowest one into 60".
If by "skillet" you mean, not a frying pan but a griddle, I have one of those too. It's only 1" to the lip but the handle isn't coplanar with the cook surface and increases the overall depth to 2".
So just out of curiosity, what are you thinking of with this plan?