Does welding on stainless rod cause substantial weakening
Does welding on stainless rod cause substantial weakening
(OP)
Hi
I have built a sculpture which is supported by a 1.5" diameter, 316 stainless rod. There is a square stainless tube welded to the rod and the welds are completely around the circumference of the rod. The rod (4 feet in length) supports a 7 foot long, 110 lb. dolphin sculpture. The 1.5" rod is sufficient to support the sculpture, but I have been hearing that the welds, around the circumference of the rod, have weakened the rods tensile strength. I am trying to gauge whether the welds have compromised the rod's ability to support the sculpture in adverse conditions. I am trying to ascertain whether the welds will cause the rod to snap or just bend should it be overloaded? Any thought would be appreciated.
Thanks
I have built a sculpture which is supported by a 1.5" diameter, 316 stainless rod. There is a square stainless tube welded to the rod and the welds are completely around the circumference of the rod. The rod (4 feet in length) supports a 7 foot long, 110 lb. dolphin sculpture. The 1.5" rod is sufficient to support the sculpture, but I have been hearing that the welds, around the circumference of the rod, have weakened the rods tensile strength. I am trying to gauge whether the welds have compromised the rod's ability to support the sculpture in adverse conditions. I am trying to ascertain whether the welds will cause the rod to snap or just bend should it be overloaded? Any thought would be appreciated.
Thanks





RE: Does welding on stainless rod cause substantial weakening
Mike Halloran
Pembroke Pines, FL, USA
RE: Does welding on stainless rod cause substantial weakening
The reason that I say prob not is that the rod is likely annealed material to begin with. Since this is the lowest strength condition there is will not be a reduction in strength.
My concern is if the bracing system has created too much localized loading or bending moment.
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Plymouth Tube
RE: Does welding on stainless rod cause substantial weakening
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: Does welding on stainless rod cause substantial weakening
Thanks
RE: Does welding on stainless rod cause substantial weakening
RE: Does welding on stainless rod cause substantial weakening
There is a big difference in mag. between annealed WROUGHT 304/316 and cast/weld metal. When 316 is poured, it solidifies in two phases, the non-mag. austenitic phase and the very magnetic ferrite phase. The ferrite phase is usually ~10-20%.
HOT working usually converts the ferrite to non-mag. aust. Cold working will convert some of the aust. to magnetic martensite. Heavily cold-worked 316 can be strongly magnetic, so a good magnet will stick very well.
316 SS weld metal usually has ~5-15% ferrite in it to prevent weld cracking, so it will be slightly magnetic.
Do you know if the design required cold-worked 316 or not?
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: Does welding on stainless rod cause substantial weakening
Often the rotary straightening of SS bar in enough to leave the skin slightly magnetic.
When you weld another transformation happens, some ferrite remains in the welds. We usually want this because it helps minimize weld hot cracking. The ferrite is magnetic also.
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Plymouth Tube
RE: Does welding on stainless rod cause substantial weakening
Nice sculpture, BTW.
TTFN
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RE: Does welding on stainless rod cause substantial weakening
is cold drawn, not sure what that means. The adverse conditions could be winds of 40-50mph, however unusual here in San Diego .
I guess my biggest concern would be of the rod snapping,
if it just bends no one would get hurt, as it is up high.
Any and all comments/thoughts are welcome
thanks
RE: Does welding on stainless rod cause substantial weakening
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: Does welding on stainless rod cause substantial weakening
it should still bend?
Per the web, 316 stainless has these properties:
- tensile strength is 85,000 pounds per square inch
- Tensile Yield Strength (.2% offset):
276 MPa / 40 kpsi
- Ultimate Tensile Strength:
621 MPa / 90 kpsi
RE: Does welding on stainless rod cause substantial weakening
There is one thing that could be a problem. When 316/304/etc stainless is welded, it can be "sensitized" in the HAZ (heat affected zone), a narrow area right next to the weld metal. The amount depends mostly on the amount of carbon in the rod. Anything more than ~.035% C can easily have sensitization. The upper limit for C in 316 is .08%, and it readily sensitizes.
What happens is that the sensit. area loses its corrosion resistance, and something called SCC (stress corrosion cracking) can occur, especially if chloride ions (cl-) are present, such as seacoast area outside. If such cracking gets deep enough, the rod could suddenly snap off.
If there is a small extra piece of the rod available, a met. lab. can perform a test to measure the amount of C. Unfortunately there is no really good method to do this outside a lab. What should be done, if the rod is outside, is to have a simple dye-penetrant test performed on the
HAZ area if it's accessible.
There are other mitigation methods, but they all require access to the weld area.
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: Does welding on stainless rod cause substantial weakening
This material has so much ductility that even if there was some surface cracking it wouldn't concern me too much. There will be a lot of bending before things break.
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Plymouth Tube
RE: Does welding on stainless rod cause substantial weakening
RE: Does welding on stainless rod cause substantial weakening
The rod is cold drawn but no cold finishing.
The 1.5" rod goes thru the full length of the square tube,
which has a .25" wall.
There is a .125" thick plate (with a 1.5" hole in it and the shape of the square tube)that abuts the rod/tube joint. So, there is a fillet weld between the rod and the plate and another weld between the plate and the tube; not sure if I desrcibed this correctly.
There is also another plate and welds where the rod exits the other end of the rod.
There are also a few plug welds half way along the 9" square tube.
Thanks
RE: Does welding on stainless rod cause substantial weakening
RE: Does welding on stainless rod cause substantial weakening
As already mentioned, it needs a detailed analysis, which should include estimation of natural frequencies and at least an educated guess at the aeroelastic behavior of the multiple cantilevered objects.
This forum is not the appropriate vehicle for that.
Mike Halloran
Pembroke Pines, FL, USA
RE: Does welding on stainless rod cause substantial weakening
- what type of engineer would be appropriate
- how does one find a qualified engineer in the San Diego area
- what would you estimate the cost of such a study to be
thanks
RE: Does welding on stainless rod cause substantial weakening
Ask the folks there to suggest someone.
Or, now that we know where it is, maybe someone will speak up.
Mike Halloran
Pembroke Pines, FL, USA
RE: Does welding on stainless rod cause substantial weakening
Natural frequency is my only real concern. If it gets vibrating a lot of stress can be set up.
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Plymouth Tube