Source
r/AskEngineers•
Szos

Trying to get specifications on black steel pipe schedule 40 (commonly used in plumbing applications). Anyone work in this industry?

Mechanical

This stuff:

https://www.homedepot.com/p/LDR-Industries-3-4-in-x-1-5-ft-Black-Steel-Schedule-40-Cut-Pipe-306-34X18/100569303

Per the Depot site, it is made according to ASTM A733 specifications, but to read those, it looks like ASTM charges you (according to their website).

I have a DIY project where straightness is important and I would like to use some of this pipe, but I'd be curious what kind of tolerance these pipes are made to. Specifically interested in concentricity and straightness of the pipe. I have a roughly 18" long piece but since I am working from home I don't have access to any of the indicators in QC we have at work to see how straight it is. Also this particular DIY project would involve longer pieces, I'm not even sure if there is a specific section within the ASTM A733 guidelines which say that it has to be within .XXX" in straightness.

In short, how straight is black steel pipe usually?

Posted Apr 5, 2020, 12:28 AM UTC

411
BadderBananaWelding Engineering•

I think A53 is the applicable spec and it says "The finished pipe shall be reasonably straight" in section 12.6. I shit you not, the spec is reasonably straight.

LMK if you know some specific keywords to search. I'm logged into my IHS and well.... don't have anywhere to go....

11
SzosOP•

"reasonably straight"

Of course!

Thanks for checking. I don't think I'll get anything from the specifications, I guess. I might just have to just buy some see how they are, but since we are in quarantine I can't run an indicator on them to see how off they are from straight.

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[deleted]•

[deleted]

2
dipherent1•

You will be better off searching for round HSS tube.

Black pipe is typically A35 which is poor for structural applications because it's developed for pressure piping. Because of application, it's fully painted which requires removal for welding, plus the strength is low at 35ksi, and the specs for straightness are very loose.

Moving to A500 HSS will bump you into structural tubing with 42-46ksi minimum strength while also being cheaper to buy (since it hasn't been prepped and painted), cheaper to fab with, and cheaper to paint, while also having tighter geometric tolerances for roundness, wall thickness, and straightness.

Round HSS is somewhat of a nuance to find. Hardware stores will look at you sideways but reputable metal suppliers will have plenty of stock for sizes similar to Sch. 40. It's the best choice.

3
SzosOP•

Does this constitute Hollow Structural Steel tubing?:

https://www.lowes.com/pd/Hillman-1-in-W-x-6-ft-L-Plain-Hot-Rolled-Steel-Weldable-Square-Tube/3054845

1
dipherent1•

It does. A500 structural tube can be round, square, or rectangular. A500 is the spec that you're looking for. There are many categories that fall under this spec such as square or rectangular stock commonly used in architectural structures and round stock which is prevalent in applications ranging from structural rigging to automotive roll cages.

2
SzosOP•

Thanks for the info!

1
I_Forge_KC•

I built a CNC router with black iron for guides. The longest dimension was 48" effective, so the total span was like 60". In that span, it was something like +/- 0.01" run-out. The design was able to use a guide block at the midpoint that helped reduce that. The machine trams at 0.028" total deflection - well within my plywood and black iron with skateboard bearings tolerance.

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SzosOP•

Well this is exactly the project that I'm looking into!

A lot of people use aluminum extrusion which should be very dimensionally accurate, but I also want to price it out compared to pipe which I assume should be cheaper and much stiffer.

Ultimately I might need to use a combination of these material to balance cost vs accuracy and stiffness.

1
MoreAlphabetSoup•

It's typically as straight as a carpenters level, if that helps. I've never seen straightness specified in a pipe astm standard.

1
SzosOP•

If be thrilled if it was that straight.

I was going to just hit up Depot and borrow a straight edge from their tool department and see if I could see light between them, but what with everything going on with Corona this might be a little bit of a PITA.

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Sinoeth•

The longer they are the more tolerance it has.

1