It is acceptable but why would you consider this.

Sch 10 may not be as readily available as other pipe. You only need a small quantity. More supports may be required. Service life will also be less (exterior corrosion).

Also cost to paint the pipe will add to overall cost. Why not use spiral wound stainless steel?

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King
http://waterhammer.hopout.com.au/

Stainless steel is what one would normally use.

I would normally use SS, but the contractor has an abundance of carbon steel piping and was wondering if he could use it instead. If I were to use SS, it would be sch 10 as well so using sch 10 CS would not require any additional supports than what is already budgeted/planned.

Primary considerations in piping materai selection are strength and potential corrosion, thermal effects and environmental factors. Piping materials typically used include carbon steel, stainless stee, ductile iron, FRP, HDPE, and PVC. Use of thin walled pipe requires that it be properly protected from physical damage. Blower discharge may be in excess of 200 degrees so the pipe and supports must be designed accordingly. Because of the large thermal stresses, provision for pipe expansion and contraction are necessary. Blower discharge is often insulated to protect workers from possible burns, help attenuate noise, and keep blower room temperaturs under control.

Blower droplegs are usually PVC or Stainless Steel because of corrosion concerns.

Don't see any benefit in your case for accepting carbon steel. You paid for stainless and a contractor typically will not give you full value back on a change order. Sch 10 is also acceptable for stainless steel because stainless steel will not corrode like carbon steel does. for that reason, the equivalent pipe to sch 10 stainless steel is sch 40 carbon steel.

You can get SWSS in a thinner wall thicknesses than shcedule 10s and thus reduce you installed costs significantly. You are not going to have great pressures in the piping system. The contractor having lots of carbon steel is like saying he has a stack of cardboard boxes or used panty hose can he use them? Ridiculous concept.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King
http://waterhammer.hopout.com.au/

Agree with the two posts above by bimr and stanier. So what if the contractor has CS pipe laying around. Are you going to redo your heat expansion and insulation requirement calcs? Will the contractor pay for that? What about corrosion concerns?

You (and the owner) have little to gain and-potentially-lots to lose by accepting CS instead of SS w/o making sure that the risks are addressed.