How much seam root will I find inside Sch 40 pipe?

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I have a project that asks for two lengths of pipe to telescope for length adjustment. I am looking for smaller pipe to slide inside larger pipe without excessive sloppiness. Total adjustments needs to be 2 feet from minimum to maximum, no less than 12" length of small pipe inside the larger pipe.Choices are A: 2-1/2" inside 3" or B: 3" inside 3-1/2".Specs for sch 40 pipe of those sizes (from Engineeringtoolbox.com)Nominal     OD        ID2-1/2"      2.875     2.473"           3.5         3.073-1/2      4.0        3.55A: If I try to slide the 2-1/2" pipe inside 3" pipe the spec shows 0.195 clearance (0.0975 all the way around)  which looks like plenty of room, almost a sloppy fit.B: If I try to slide the 3" inside 3-1/2" pipe the spec shows 0.050 clearance (0.025 all the way around) which looks almost snug.  But what of the root bead from the welded seam during manufacture?  Regrettably I do not have much opportunity to view or test fit before making a purchase.Any suggestions? - MondoMember, AWSLincoln ProMIG 140Lincoln AC TombstoneCraftsman Lathe 12 x 24 c1935Atlas MFC Horizontal MillCraftsman Commercial Lathe 12 x 36 c1970- - - I'll just keep on keepin' on.
Reply:I believe you will be unhappy with scd 40 pipe.Seamless tubing is what you want. The fit will be predictable and consistent.Drawn over mandrel (DOM) tubing is what it will likely be listed as.Last edited by MinnesotaDave; 05-21-2021 at 07:08 AM.Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:Thank you for the response.Yes, I am familiar with DOM tubing. The problem is DOM is not available at my local steel supplier. I would need to get is shipped in from I don't know where and that adds expense. The project does not require that much accuracy, a sloppy fit will work, I am just trying to limit the sloppiness. - MondoMember, AWSLincoln ProMIG 140Lincoln AC TombstoneCraftsman Lathe 12 x 24 c1935Atlas MFC Horizontal MillCraftsman Commercial Lathe 12 x 36 c1970- - - I'll just keep on keepin' on.
Reply:You can get seamless sched40 pipe. Also most erw sched 40 pipe is skimmed on the inside to remove the seam. It's usually down grade pipe that has the seam remaining. Can't speak for pipe from you know where though, that can be anything.
Reply:Thank you! This is good info. I will ask for seamless sch 40 pipe when I call my supplier. - MondoMember, AWSLincoln ProMIG 140Lincoln AC TombstoneCraftsman Lathe 12 x 24 c1935Atlas MFC Horizontal MillCraftsman Commercial Lathe 12 x 36 c1970- - - I'll just keep on keepin' on.
Reply:I would simply build up 3 or 4 areas with weld and grind to fit . If you do that in 2 spots along the length you can get whatever fit you desire. Depending what it's for duct tape wrapped around may also work.
Reply:You can go with oilfiled tubing also. 2 3/8 tubing will fit inside 2 7/8 tubing just fine. Finding any larger than 2 7/8 will be difficult.Another trick - grind a groove in the inner pipe to clear the seam on the outer pipe. Has an added benefit of preventing twist in the slip joint.I also saw a video where a guy built a seam shear out of a disk & an allthread that would skim the seam out of the pipe (or sq tubing in the video - looked like a pretty simple tool to build.
Reply:Originally Posted by MondoThank you! This is good info. I will ask for seamless sch 40 pipe when I call my supplier. - Mondo
Reply:Originally Posted by M J DI would simply build up 3 or 4 areas with weld and grind to fit . If you do that in 2 spots along the length you can get whatever fit you desire. Depending what it's for duct tape wrapped around may also work.