Black Iron Pipe vs Galvanized Iron Pipe as structural members for long span trusses

[SatoshiNakamoto09]

I have designed a 60m long span truss with box-type built up pipes as structural elements.
In terms of strength, does it matter if the pipe used in site will be B.I pipe or G.I pipe?

Am I right that what matters is the steel yield strength I used in the design calculations?

 

[BridgeSmith]

For design, I don't think it matters. If it's going to be welded, the galvanizing would have to be removed from the areas to be welded.

 

[1503-44]

May be better to develop a material specification that will set the material properties and pipe fabrication process and quality you require. "Black pipe" includes material that has little to no control of material composition or properties, or fabrication, or anything. You may be hard pressed to acquire any proof of yield strength whatsoever. 60m span could involve significant risk for a minimal strength, no QC, basically unknown material.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

I agree, what matters is that the pipe you build it from is the strength and weight that you have used in the design.

B.I. and G.I. are very vague specifications and can vary wildly.

Also if this is outside anything "Iron" might be subject to brittle failure in very low temperatures.

Is this a continuation of the previous thread?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[DTS419]

In many applications, the galvanizing is applied by dipping the base metal (see hot-dipped galvanizing); it is just a coating and does not change the material properties. Of course you'll need to confirm that with the pipe manufacturer. If this will be welded, you'll also want to watch the carbon content. Many "iron" products have a higher carbon content than familiar steel alloys which can affect weldability.

 

[1503-44]

It's often, but not necessarily associated with ASTM A53, a low quality requirements spec, and really is suitable only for very low pressure applications, mostly plumbing related. I would say it is probably not suitable for structural use at all.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[JLNJ]

For a serious structure, I'd spec ASTM A500 round sections. We have used A53 pipe in "structural" applications for decades, but A500 is a better option (for the reasons stated above).

 

[BridgeSmith]

I agree that for structural applications, ASTM A500 round HSS is the way to go, unless you want weathering steel, in which case you'd spec ASTM A847.