Help with weld design

[serlarra]

Hi,

I just been asked to calculate the minimum size required for a slot/plug weld to attach a pipe to a plate. I’ve never designed welds so I’m new at this.

I started by reading AWS D1.1 to find the max/min allowed sizes for the slots/plugs. Then, I couldn’t understand how to calculate the actual area needed so I went back to the internet and found an article about weld calculations using “Mean Stress Method”. After doing the calculations I ended up with an area of 0.02 in², which I found unrealistic.

Could someone point me in the right direction or tell me the equations to find the required area?

The pipe is welded horizontally to a steel plate of 3/8” and when filled weights around 200 lb.

 

[epitome1170]

It sounds like this would be a flare bevel weld and not a slot weld.... can you provide a sketch (a picture if worth a thousand words)?

I would use AISC specifications for weld strengths... chapter J.

 

[serlarra]

Hi epitome1170,

I made a quick draft of what I'm trying to do. The side with the pipe is hard to access when assembled, that is why we want to use slots/plugs.

I'm still going to look up the specifications you suggested.

 

[epitome1170]

AISC will give you the equations and safety factors for the slots/plugs.


And yes, that type of weld makes more sense after I saw the sketch.

 

[nutte]

The force you're trying to resist is only 200 pounds? If that's the case, it's not at all surprising that your required area is almost zero.

 

[epitome1170]

True, nutte... I missed that little bit of information.

 

[serlarra]

Thanks for the input,

One more thing, the structure will be summited to thermal fluctuation from around 75°F to 150°F (Delta_T = 75°F).

I calculated the thermal stress ass f=(a)(delta_T)(E) which gave me a 15ksi stress. Would this be relevant for the design?

 

[boo1]

same materals grow at same rate

 

[Guest102023]

Please examinine your company's tolerance for risk, details of their insurance, and your own competence to tackle this. Design calculations are the last thing you should be enquiring about on these forums.

 

[Ron]

brimstoner....disagree....design calcs are routinely discussed here. Engineer-to-engineer...anything is open for discussion. This is certainly relevant and capable of being discussed in this forum.

serlara...your stress level is low, so you really just want to make sure that your weld doesn't screw up something else. A simple plug weld is relevant and check the AWS requirements.

 

[csd72]

You also need to account for the eccentricity of the load as the weight is applied at the middle of the pipe but the support is at the edge.

Conservatively I would add the shear from the thermal expansion/contraction forces on to the weld shear.

I would also note that very small welds are not a very good idea as the first 0.25 to .5 inch of weld is not always fullty effective as the electrode is not always fully heated or lined up properly. I expect if you did specify a very small weld the welder would tend to make it larger for this reason.