HSLA pipe satisfies load requirements 1

[blakesteel]

I was reading this thread about how regular pipe does not satisfy the load requirements of the standard specs used:

http://www.eng-tips.com/viewthread.cfm?qid=405072

I meant to just reply in that thread but it is closed.

My supplier has been selling me HSLA pipe that has a much higher stress yield and therefore satisfies the standard load requirements.

If one looks over how NAAMM handles the calculations for this thing:

https://www.naamm.org/store/product/4/pipe-railing-systems-manual

One sees on page 19 of that manual (page 22 of the PDF) that the pertinent equations are:

1. For uniform loads:

   w * l * h = 12,000 * S * Fb

   where

     w  = uniform load requirement to satisfy in lb/ft (usually 50 lb/ft)
     l  = post spacing in inches
     h  = height of rail in inches
     S  = section modulus of post in in^3
          reference = [URL unfurl="true"]https://en.wikipedia.org/wiki/Section_modulus[/URL]
     Fb = bending stress in ksi
        = 0.72 * Fy according to footnote 1 on the previous page
          where Fy = yield stress

   My supplier gets the HSLA pipe I buy from Bull Moose Tube:

     [URL unfurl="true"]http://www.bullmoosetube.com/references/documentation[/URL]

And for the 1-1/4" sched-40 ASTM A500-13 HSLA Grade 50 round tube that I am buying it has a stress yield of 70,371 psi. So one can use an Fb of (0.72 * 70.371) ksi = 50.667 ksi for this round tube.

This 1-1/4" round tube has a wall thickness of 0.13" and not the standard 0.14" of the Grade B tube. And therefore its sectional modulus is 0.222 in^3 - not 0.235 in^3.

So if one were to make a 42" high guardrail out of this round tube and needed to satisfy a uniform load requirement of 50 lbs/ft, you could space the posts:

   l = (12,000 * 0.222 * 50.667)/(50 * 42) = 64.28"
     = more than what people usually make the post spacing (about 5 ft o/c)

For a round tube with only a 30 ksi Fb (50 ksi stress yield) you could only have a maximum post spacing of 40.29" = less than what is normally done. That is what that thread is talking about there. This HSLA tube is fine for standard post spacings though.

2. For a concentrated load, that NAAMM manual uses the equation:

   P * h = 1,000 * S * Fb

where P is the load applied to any post in lbs (a percentage of the required load depending on the geometry of how that load applies).

For the 42" high guardrail of this material, it could handle 100% of:

   P = (1,000 * 0.222 * 50.667)/42 = 268 lbs
     = well within a spec of 200 lbs even if ALL applied to the post considered.

Therefore, one can just use HSLA round tube for pipe rails and avoid the problems brought up in that thread.

This is important info to know because everyone has come across this problem of standard pipe not meeting spec. HSLA pipe meets spec and is only about 5 cents a ft (about 2 cents a lb) more in cost.

 

[BAretired]

And for the 1-1/4" sched-40 ASTM A500-13 HSLA Grade 50 round tube that I am buying it has a stress yield of 70,371 psi. So one can use an Fb of (0.72 * 70.371) ksi = 50.667 ksi for this round tube.

Grade 50 has a yield of 70 ksi? Are you sure that is the guaranteed yield stress?

BA

 

[IFRs]

Good to know, thanks. Years ago I standardized railings for a company, we used 1 1/2" because 1 1/4" did not pass. I was a younger engineer at the time. Never thought about it much since then...

 

[TLHS]

That callout's wrong, but such a thing does exist. I suspect he's talking about high strength/low alloy steels fabricated to the dimensional requirements of A500 tube, but at 70ksi yields.

For example

https://www.independencetube.com/downloads/Shapes/HSLA.pdf

 

[blakesteel]

Yes, it's weird that a "grade 50" steel is 70 ksi yield strength. HSLA is "high strength low alloy" as TLHS says. The bending stress is 50 ksi - maybe that is why they're calling it "grade 50" in the attached test report.

I didn't see that one can upload files here. I'm attaching the NAAMM manual, the certification tests, and the sectional properties.

http://files.engineering.com/getfil...79-42b0-ab4e-53885600b6e8&file=amp_521-12.pdf

http://files.engineering.com/getfil...5ae-4c84-8d46-5bf052bb648b&file=hsla-pipe.pdf

http://files.engineering.com/getfil...e=HSS_Dimensions_and_Sectional_Properties.pdf

 

[TLHS]

There isn't an ASTM A500 Grade 70. So I suspect they've certified it to Grade 50, because why not, but then are testing it and selling it as a higher capacity. It's a confusing way to label it though.

Am I the only one that's worried that the ultimate tensile capacity is only 5% above the yield capacity (73.7ksi)? It looks like there's a fair amount of elongation, so there's ductility... but still? You aren't getting strain hardening out of this material. You might make some really bad assumptions about connection behavior, especially.

480W (weldable 480MPA/70ksi yield stress steel) to CSA standards would need to have a minimum tensile strength of 590MPa/85ksi.

Maybe this doesn't matter for handrail applications, but it's not great.

 

[wannabeSE]

I think the supplier is a little fast and loose with their material specifications. ASTM A500 has letter grades (A, B, C, D). So to say ASTM A500 grade 50 is odd. Also, ASTM A500 rounds are specified by outside diameter and nominal wall thickness. So, saying 1-1/4 sch 40 meets ASTM A500 size requirements is a bit odd. Adding HSLA (high-strength, low-allow) to the mix seems to be more marketing. There are different ASTM specifications for high strength low alloy steel. But the supplier doesn't reference any standards. More info on HSLA at

http://www.asminternational.org/doc... 3B.pdf/a764507a-3499-4d23-b348-5536d31c0ba2.

OK, so this stuff yields at 70 ksi, the architect will be happy with the skinny post and scoff at all of the conservative engineers in his past.

I am curious about the cost. Does the high strength 1-1/4" pipe cost less than typical 1-1/2" pipe? How are the connections working out? If the post is cantilevering from a base plate, a larger diameter post helps reduce the weld size. With a somewhat dubious material specifications, do you assume it is a group II base metal for prequalified welds.