Osama, my point was that welds thicker than it is required from static stress design, are sensible only when fatigue comes into play. Since, as you say, there is no fatigue issue anicipated, you don't need to increase the weld size. If your client needs longer protrusion than the weld leg length- you better ask what for. As Niraj rigthly points out, draining of the upper tubesheet with some protrusion gets problematic. In my opinion, the same will apply to venting of the bottom tubesheet (and when bubbles gather outside of the tubes, under the tubesheet, you are inviting the corrosion)

By the way: your original question appeared here 20 days ago and you don't seem to communicate with your client, facing an unsolved and seemingly weird problem. Haven't you got any chance to contact anyone who knows what they want?


No, I meant that if the strength of the joint is higher than the strength of the tube itself, the tube will statically break prior to the weld.



Of course, it's always good to have some reason to make any overdesigned stuff. In my opinion, some premium in the price is a reason good enough to do it, provided it's doable at all

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Konrad Anikiel

Konrad,

Please conclude that whether i should go for this type of protrusion or if it not recommended or if it is not a good practice, then why in any condition it may be allowed.

Simply according to you, if throat size increases the overall weight of the joint and eventually the cost, and if it will break the weld anyway, then i should simply argue with my client and communicate that same cannot be performed !

Please give me some reference if "tube is protuded then it is going to break prior to weld"

Appreciate your response, please

_________________
Syed Osama Nusrat Ali
Exective Engineering (Project)
Fauji Fertilizer Company Limited
Pakistan
email: osama_ali@ffc.com.pk
Cell # +92-3025252018

Osama,
The increased protrusion itself does not increase strength of the joint. It only leaves more space for a thicker weld. If (repeat: IF) you make 5 mm protrusion and (repeat: AND) 5 mm weld- it will increase the strength of the joint when compared with, say 3 mm. Please, don't read between the lines, there's nothing more written down. My private rule of thumb is, the Fig. A-2(1) with weld throat>t is overdesigned as long as static load is considered.

Whether you want to do something this way or that way- sorry, I will not tell you what to do. I can tell you what would I do. I would talk about it to the client first. You have a binding contract, you have to fulfill what your salespeople agreed to. You have to make the right engineering judgement- if you wilfully decrease the degree of safety and if it fails catastrophically- well, I think prisons in Pakistan are not very cosy...

PS telling your client that something cannot be done does not raise your value in their eyes as a competent engineer

_________________
Konrad Anikiel

KONRAD,

Thankyou very much

Discussions were very interesting and i have got the basis for deciding for the protrusion.

I think i will conclude as follows:

" The increased protrusion only doesn't affect the strength of the joint. The cooling rates in a fillet weld are relatively greater and this fact means that risks of cold cracking are more likely increased in alloy steels. This is in addition to the possibility of very large fillet welds may cause unacceptable distortion and or extremely high residual stresses.

Although the throat thickness is regarded as being the most important dimension for the design purposes it is a fact that mechanical failure of fillets welds is often being along the fusion line or the through base metal itself One reason for this is that in alloy steels the weld metal is mostly substantially stronger than the base metal.

Moreover, the actual throat thickness is always greater than design throat thickness and excess weld metal of the weld gives no benefit with respect to the design strength and from cost point of view it is not justified.

Finally, when deciding on the size of the fillet weld it should be remembered that a small increase in throat thickness will result in disproportionately large increase in deposited weld metal. Roughly increasing the throat from 5mm to 6mm results in an increase of around 45%. This equates to almost 0.1kg extra weld metal per 1 metre length of weld. So there are extra substantial cost and weight penalties to be paid if the joint is made heavier by the designer or over-welded by the welder / fabricator."

_________________
Syed Osama Nusrat Ali
Exective Engineering (Project)
Fauji Fertilizer Company Limited
Pakistan
email: osama_ali@ffc.com.pk
Cell # +92-3025252018

Osama,
That's all correct. You aren't making a doctoral thesis by the way, are you?

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Konrad Anikiel

Thankyou Konrad,

I am late in reply. I was busy in some other thing.
Regarding thesis , i always work like we did work on thesis.

You were very cooeperative in the complete session.

Thanks once again.

_________________
Syed Osama Nusrat Ali
Exective Engineering (Project)
Fauji Fertilizer Company Limited
Pakistan
email: osama_ali@ffc.com.pk
Cell # +92-3025252018