I recently had the opportunity to design a lifting beam that had to be rated to -45 degrees C. Although this might not be super common around the world for equipment designed and used in Canada this pops up occasionally. In this article I will discuss some of the flaws in the low temperature thinking, how we make low temperature rated equipment and why it matters.

The Science Part

So what happens when it gets cold? The molecular structure of various materials can organize themselves in one of two primary crystalline structures called body-centrered cubic (BCC) structures and face centered cubic structures (FCC). I am not going into a lot of detail on this. If you are interested you can read this good summary here: The important thing to know is that most steels are body centric cubic structures and they undergo a transition called the ductile to brittle transition. This transition, abbreviated as DBTT, describes the temperature when a material transitions from behaving ductile and starts to perform in a brittle nature. This means that the static strength of the material might increase but its ability to absorb impact energy is drastically reduced. This poses a critical risk for lifting equipment as it exposes people to a risk of sudden and catastrophic failure when the temperature is low even at a load that the equipment is otherwise rated to operate with.

Borrowed without permission from: http://www.materials.unsw.edu.au/tutorials/online-tutorials/2ductile-brittle-transition

Face Centric:

  • Aluminum
  • Copper
  • Lead
  • Nickel
  • Silver
  • Austenitic stainless steels

Body Centric:

  • Lithium
  • Sodium
  • Chromium
  • Iron
  • Tungsten
  • Many common ferrous alloys

What does the code say?

Asme B30.20 & BTH-1 say in clause 1-4.7 that the design provisions in this standard are considered applicable when the temperature is in the range of 25 to 150 degrees F or –5 to 66 degrees C. For equipment operating outside of this range special considerations need to be made. Which is why this article exists. I think people working with low rated equipment need to know some of what goes into getting the temperature rating different than what is said in the code.

 

Low Temp. Required – What to do

If you absolutely need a low temperature piece of equipment there are a few steps to take. The first and most important to pick a temperature to design to. In my experience the common ones for around here are -20 degrees C or -45 degrees C but this should either come directly from the end user or from published temperature data.

The next step is to find a suitable material to manufacture the equipment out of. This is really where some value can be added to the process. There are a few paths you can take for selecting material. If possible you can select a material that doesn’t go through a brittle transformation such as aluminum. If this fits the project then there are no more issues. More likely you are going to be looking for a steel material that is suitable at your design temperature. Some materials have great low temperature properties and MTRS that include a test performed at a cold temperature. Often you can sift through a few MTRs from your steel supplier and find one that has low temperature impact testing done at the temperature required. I often default to a quenched and tempered steel such as QT-100 in this case which has a service temp of -45 degrees C and other mechanical properties that are great for lifting equipment.  The last situation you might get into is that you need a cold temperature rating on a very specific material and you must hire a lab to perform the tests. I was involved in one situation like this with a 4140 shaft that we required to have certain cold temperature performance this process was expensive and time consuming and might not be justifiable on the average project.

The last step of the process is to make sure all of your supporting equipment such as rigging, pins and manufacturing process also meet the cold temperature requirements of the project. Crosby has a line of “cold tuff” shackles that are rated down to -50 degrees F that are relatively affordable but you will have to check the other rigging on a case by case basis.

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The Philosophic Problem with Low Temp Lifting Equipment:

I want to share what I feel is the problem when companies request low temperature lifting equipment but do it in a way that doesn’t diminish the risk or sound too controversial. It is important to consider all the risks and build equipment appropriate but what I find is companies will request either a temperature that is arbitrarily low or they haven’t low temperature the whole path of the load.

When a company selects an arbitrarily low working temperature I believe that in most cases it’s a desire to remove all risk of the project without understanding exactly how difficult (or close to impossible) to find material that can perform at super low temperatures such as -50 or -60 degrees C. Unless you are in an extreme situation or in an extreme spot in the world I don’t know too many people or machines that work in -60 degrees C weather and unless the job warrants it the difficulty of finding the correct material could more than triple the cost of the device. I was recently designing a lifting beam that was required to be -45 degree rated but it was a single use device used to install a skid once. -45 degrees isn’t to bad to achieve but on a one use spreader bar could we not just pick a warmer day to install it?

The other situation I see a lot is a company will specify a low temperature lifting equipment without following the whole load path of the lift making sure each piece of equipment is rated to work at a given temperature. My favorite example of this is crane blocks. All the crane blocks I have seen have a -20 degrees or warmer minimum working temperature. I am sure you can buy a crane block that is low temperature rated but does it make sense to hook a -45 degree rated lifting beam onto a -20 degree rating crane block?

I hope you enjoyed this article. If you have any questions or comments feel free to let me know. Keep your eye out to cold temperature rated lifting equipment drawings in the store. If you need help dealing with a low temperature requirement please reach out to me and maybe I can help.

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