A pipe has a thickness designation of '40S'. What does the 'S' mean?

A pipe has a thickness designation of '40S'. What does the 'S' mean?

• A. Stainless steel
• B. Schedule
• C. Steel
• D. Special

Answer: (A)

In pipe designations, the numeric part tells you the wall-thickness class (schedule), and the letter suffix indicates the material type. So 40S is Schedule 40 stainless steel pipe—the S flags stainless steel, distinguishing it from carbon steel or other materials. This matters for corrosion resistance, strength, and applicable standards in piping inspections. The other ideas—that the S means schedule, steel in general, or something like special—don’t fit because the 40 already represents the schedule, and the S specifically denotes the stainless material.

In pipe designations, the numeric part tells you the wall-thickness class (schedule), and the letter suffix indicates the material type. So 40S is Schedule 40 stainless steel pipe—the S flags stainless steel, distinguishing it from carbon steel or other materials. This matters for corrosion resistance, strength, and applicable standards in piping inspections. The other ideas—that the S means schedule, steel in general, or something like special—don’t fit because the 40 already represents the schedule, and the S specifically denotes the stainless material.