Effect of torch cutting steel for reuse
Effect of torch cutting steel for reuse
(OP)
Working on a lifting attachment for a client who is lifting large steel assemblies.
The base plate of the attachment will need to be welded on to an assembly, used to lift the assembly, and then cut off for reuse on subsequent assemblies.
The client has asked "if we torch cut off the base plate, what effect will this have on the strength of the steel in subsequent uses?" I'm at a loss with my experience to know what, if any, effect torch cutting steel would have. My instinct tells me it will likely make the base plate more brittle as time passes, but how to quantify this into a replacement schedule is beyond me.
Any thoughts?
The base plate of the attachment will need to be welded on to an assembly, used to lift the assembly, and then cut off for reuse on subsequent assemblies.
The client has asked "if we torch cut off the base plate, what effect will this have on the strength of the steel in subsequent uses?" I'm at a loss with my experience to know what, if any, effect torch cutting steel would have. My instinct tells me it will likely make the base plate more brittle as time passes, but how to quantify this into a replacement schedule is beyond me.
Any thoughts?
PE, SE
Eastern United States
"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi





RE: Effect of torch cutting steel for reuse
Best regards - Al
RE: Effect of torch cutting steel for reuse
If the alloy is rich enough that it will air harden then you could have issues.
If possible I suggest a test, weld and cut and weld a number of times, and then check the strength and toughness.
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Plymouth Tube
RE: Effect of torch cutting steel for reuse
PE, SE
Eastern United States
"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi
RE: Effect of torch cutting steel for reuse
RE: Effect of torch cutting steel for reuse
Go with A36, but be certain you are actually getting A36!
You don't an unknown Chinese-melted copper-filled and stainless-mixed "zoo" of cast crap from melted automobiles, batteries, and seat covers.
RE: Effect of torch cutting steel for reuse
Metengr - In your opinion is there a specified distance we could call for as far as removal goes that would likely take care of the heat affected zone? I think the MT test is a good idea but would want to avoid trimming the steel, conducting the test, trimming steel, etc. I do plan on recommending the test though before the lug would be certified for reuse.
Racookpe - Interesting point here. So the lower grade steels actually work better for this? What about steel allows this to happen? (I spec the steel all the time but admittedly don't get much into the chemistry of it!) Also good point about the certified steel. This client buys steel by the trainload and we have asked before for certification sheets which aren't usually available. We typically have made them buy steel we are designing 'special order' so that we can get the certs on it.
PE, SE
Eastern United States
"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi
RE: Effect of torch cutting steel for reuse
RE: Effect of torch cutting steel for reuse
RE: Effect of torch cutting steel for reuse
PE, SE
Eastern United States
"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi
RE: Effect of torch cutting steel for reuse
Chemistry is important when considering the affects of heating and cooling steels from the austenitizing temperature range. The cooling rate (for a given chemistry) from the austenitizing temperatures determines whether the material will become hardened or not. With the low carbon content of A36, there is little likelihood it will get hard enough to be of any concern.
The oxidized surface that results from the cutting process is detrimental to the welding operation. It should be removed down to bright metal to ensure the welder has a fighting chance of depositing a good weld. Inadvertent notches should be faired by grinding, again, just to provide the welder with a suitable surface for welding.
Thick plates should be preheated to the same temperature as welding, i.e., if the applicable welding standard requires preheat prior to welding, the same preheat can be used prior to torch cutting.
More often than not, the removal of the previous weld will remove any heat affected zone associated with the initial weld. The HAZ that results for the torch cutting operation will be not more detrimental than the HAZ from welding. It may extend slightly deeper into the base metal, but if the welding doesn't produce any problems, neither should the torch cutting.
Best regards - Al
RE: Effect of torch cutting steel for reuse
RE: Effect of torch cutting steel for reuse
A36 "ordinary" steel is adequately tough, adequately flexible, adequately strong, easily weldable, and adequate,y available. Right?
So, you really don't need to change it, to do anything different UNLESS "qdequate" is "not good enough" for the particular job you are trying to do. Right?
So, you need a non-rusting steel -> You make a more expensive stainless steel.
You need a higher strength steel -> You "make" an exotic, expensive, carefully-treated and heat-treated high carbon-moly mix with very carefully controlled PWHT. Works. Right?
You need 80,000 psi steel for submarine hulls. you invent HY-80.
You "need" low-weight alloys for aerospace -> You invent expensive mixtures and alloys.
But -IF - (big "IF" there!) - you do not need the exotic crystal pattern for the "ordinary/average/weldable/"just plain steel" that will be used and torched and welded and re-torched until no longer useable, do you really need an exotic alloy with exotic crystals and complex PWHT?
If "ordinary" steel will meet your strength and weight criteria, use it. just plan on the (very slightly higher) weight, and the specific weight required.
RE: Effect of torch cutting steel for reuse
Racook - good thoughts. In this case, and knowing this client, simple and economical is the right approach over exotic. I think ordinary steel here is the right approach.
PE, SE
Eastern United States
"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi