Despite our superhuman feats of fabrication, we’re all mortals here at Wiley, and we’ve been shivering through what feels like a long winter. That got us wondering though, we know Superman’s Fortress of Solitude is somewhere in the Arctic: how does he handle the cold?
And what if he needs to do some fabrication work outside? With his heat vision it’s likely he’s a darned fine welder but will low temperatures affect his work? Here’s what he needs to know.
With our well-heated shop, there aren’t many occasions when we need to weld outdoors, but it can happen. For example, it’s conceivable we could be asked to fabricate a structure too large to fit through our doors.
Other welders aren’t so lucky though. Take the people who work on pipelines and in oilfields. It seems like they’re either sweating in the desert or freezing in bitter cold. Then there are those in construction, who could be working on a bridge or high up on a tower.
Welding is a thermal process: we heat two pieces of metal above their melting point and let them fuse together. (Yes, sometimes we add filler too.) It seems reasonable to think then that ambient temperature will have an effect on the welding process. In fact that’s one of those most commonly asked questions about welding in the cold. Here’s our answer to that and five other frequently asked questions on welding in low temperatures, (not low temperature welding – that’s something different.)
6 Cold Weather Welding Questions – Answered!
1. What should I consider before welding in low temperatures?
There are two things to think about: your clothing and your equipment.
Clothing. You need to keep the feeling in your fingers and you can’t afford to be distracted, so bundle up. This is especially important if you’ll be working up in the air. Even just a few feet off the ground you can be catching a lot more wind and that just pulls the warmth straight out of you.
Equipment. Anything water-cooled risks freezing so make sure it’s appropriately protected. You might also note that electronic components are averse to extremely low temperatures, so if you’re going out in negative digit weather check the specs on your equipment. And obviously, batteries die quickly in cold weather.
2. How do low temperatures affect the materials being welded?
Simple answer: Most metals become more brittle at low temperatures.
More useful answer: Metals have a ductile-to-brittle transition temperature or DBTT. This is the temperature, (actually it’s more of a narrow range,) at which ductility drops off dramatically. In many steels this transition occurs at around 32°F (0°C) and it’s one of the reasons the Titanic went down so fast: the water was below the ductile-to-brittle transition temperature so the hull steel was particularly brittle.
In stainless steel, with it’s different composition, the DBTT is far lower. Typical values are around -328°F (-200°C) and not many of us are ever likely to be welding in conditions like those!
The bottom line: if you need to weld temperatures below freezing, check the material specs for the DBTT.
3. Are there any special considerations when stick welding?
Yes. The issue here is really moisture in the sticks. Temperature changes can cause condensation and that’s a bad thing. In general, keep your sticks warm and dry until you need them. You can buy special welding sticks for low temperature work if you need to. Lincoln Electric for example has their Kryo range for low temperature offshore welding applications.
4. Does temperature effect weld strength?
Yes! The issue here is cold cracking, (the term seems especially apt in this context,) caused by cooling too quickly. Rate of heat loss is proportional to the temperature difference, which tells us that in cold conditions a welded joint will cool faster. There are other factors at work too, like steel chemistry, amount of hydrogen in the weld and ambient humidity, but generally speaking, there’s greater risk of cold cracking when welding in low temperatures.
Don’t forget that cold affects the warm up side of welding as well as the cool down. If the materials being welded are very cold you’ll need to put more heat in to make a weld. In thin material the impact is pretty small but you may see a difference in big, heavy weldments.
Last, we have heard of people throwing an insulated blanket over a welded joint to reduce the cooling rate. It’s something to consider.
5. Is there a role for pre-heating?
Another emphatic yes! Pre-heating reduces the amount of stress and distortion in the weld and can also help protect against cold cracking. Welding codes usually offer guidance on pre-heating, so follow those.
Need a simple visual aid to tell if the materials are hot enough to weld? There are special crayons that melt at particular temperatures. Apply those to your workpieces and watch for the crayon to melt when the material is hot enough.
6. Do welding codes have anything to say about low temperatures when welding?
Funny you should ask, yes they do. This isn’t the place to go into details – check the applicable codes themselves for that – but we can offer some general pointers.
For those working on bridges the relevant codes say to not weld when the ambient temperature is below 0°F (-18°C.)
Codes for piping and pressure vessel work are a little kinder to the person welding. They have a minimum temperature of 32°F (0°C.)
And last, ASME welding codes say not to weld at temperatures below 50°F (10°C.)
We haven’t checked with our welders here at Wiley but we suspect they’re on the side of ASME when it comes to minimum temperature. That has nothing to do with the weld of course, and everything to do with their comfort!
Follow the guidelines
Welding is a thermal process so it’s only natural that temperature has an impact. The biggest thing is to watch the cooling rate as cooling too fast can reduce weld strength. And always follow any relevant welding codes.
As for how our Man of Steel handles the cold, well we’ve never seen him wearing a coat so perhaps he doesn’t feel it. There again, he wears his underpants on the outside so what does that say about his wardrobe and clothing sense?