Structure in Canada

[dozer]

We're bidding on structures in Canada that will be fabricated in the U.S. so we will be using U.S. procured steel such as ASTM A36, A992, and A500 Gr B. The minimum temperature at the site is -45C. These will be unheated, sometimes open structures (think pipe racks). I'm concerned these steels won't be suitable for this low of a temperature, so my first questions is have these steels been used successfully at this temperature? Are there supplements we should specify to make them suitable? If we bought steel that met Canadian specs. (whatever is equivalent to ASTM) would that simplify things since I presume low temperature is just a given up there? Are there other structural steels for wide flanges and HSS sections available in the U.S. that would be more suitable?

I know it's a lot of questions. I'm just trying to foresee some options. Thanks.

 

[jayrod12]

The canadian steel grade standard is CSA G40.

That being said. We often find ourselves using US designated steel due to availability. I cannot see the change in grade being a huge deal as long as the designer is aware prior to fabrication.

We for standard rolled shapes we use 350W steel yield strength 350 MPa, Ultimate strength 450 MPa.

If your designer has accounted for the major temperature swings then I cannot see you having any problems.

 

[TLHS]

I'm assuming you're in Fort McMurray or Fort St John if you're doing pipe racks at that temperature.

It depends what your loading looks like. For outdoor industrial structures we'll often use standard grade steel, but you start to see these steels acting in a much more brittle way when you start drifting a bit below freezing. This isn't wonderful in normal service but it becomes critical in fatigue and impact scenarios. Your fatigue service life with normal grade steel drops significantly once you get into these temperature ranges and you run the risk of a brittle fracture under impact loads.

So at a minimum, I'd normally specify a 350WT or other WT grade steel for critical areas of structures that see this kind of loading (including lifting lugs and maybe other members that could see an impact high in their stress range during lifting). It ensures you don't have a material that will see a brittle fracture in cold conditions. Some owners actually have specifications that call for this in all outdoor structures that see below a certain temperature, but that's somewhat rare in my experience.

So depending on whether you're planning on seeing a lot of vibration, or if you've got transient loads you're restraining, or have other similar load conditions there may be areas you want to consider this failure mechanism and maybe look at alternate materials.

Basically, it's a steel that has the normal requirements for a weldable grade structural steel with additional charpy impact test requirements.

 

[dik]

For outside cold critical stuff TLHS has the material right on... G40.21-350WT is what we would normally use... 350 MPa, aka Grade 50...

Dik

 

[LOKSTR]

see the attached pages from Canadian standard for your reference. You need to specify relevant V-notch requirements in your specs if the steel is exposed to low temperature all the time.

http://files.engineering.com/getfil...-4e40-90fc-eb6a0884c014&file=steel_grades.pdf

 

[dozer]

Lokstr, what do you mean by "all the time"? This is in a region where the record low temperature is -45C, so no, I wouldn't say that is all the time. In other words, it's not some process that is keeping the steel cool but rather ambient conditions. I'm use to designing in the sunny south so I'm not familiar with the Canadian code. Does it provide any guidance when to use tougher steel (like 350WT)?

Thanks for the answers so far. Very helpful. I'm still curious about using steel that conforms to US standards. Anybody use that in Canada?

 

[CANPRO]

A record low of -45C is comparable to the record low in many of the states "down there".

http://en.wikipedia.org/wiki/U.S._state_temperature_extremes

Note that many record low temperature are below -45C, so there should be some US standards that cover this.

It is not unheard of in Canada to use ASTM to specify material. I think the fabricator should be able to determine which are equivalent.

I'm not familiar with the US codes, but I suspect the difference in final design would be minor/subtle if you did two different designs with the Canadian vs US codes/standards...maybe someone who uses both codes on a regular basis could comment on that.

 

[dozer]

Hmm, you make a good point, Caneit. Maybe that was average low in the coldest month.

 

[TLHS]

There's nothing wrong with using american steels as long as you've designed for them. I'm sure you can find a charpy tested steel in the states somewhere too if you need it. You will have to design to the Canadian code, so be careful because all the tables and things are calibrated to common Canadian steels. It's pretty similar to the AISC stuff, but there are little differences hiding here and there so you can't just design to AISC and say it's equivalent.

Also, be careful at interfaces where some things are done in the American shop and some are done at the Canadian site. Also, check your contract with the owner and any design specs they have. They may have specs that require Canadian certifications for various things, which could get you into trouble. Remember that if you're doing things like site welding you'll be using Canadian welders with Canadian certifications and materials. If you're doing concrete foundations are you using Canadian or American steel?

On an unrelated note, watch that you leave space for thermal expansion on pipe racks up there. The swing in temperature over the year is easily -40 to +35 Celcius and then unpainted steel can heat up an extra 10 to 15 degrees no problem.