Dear All,

According to my understanding, the tube protruded outside the tubesheet should be 3 mm approx. What is the standard length for protuding tube outside the tubesheet. As my client wish to protrude it 5 mm.

Best regards,
Osama

Osama
How do you want to weld them? Any expanding? What is the material and other secrets about your HX?

Konrad,

1. Tube to Tubesheet joint is a strength weld as per design consideration
2. Matrl: 1.25 Cr 0.5 Mo
3. Tube is SA 213 T11
4. Tubesheet is SA 336 Gr 11 Cl 2
5. There is a light expansion in Tubesheet
6. Tubesheet thickness is 130 mm and light expanison is around 110 mm

I belive client is asking for 5 mm purely Due to Process requirement.and you have to provide.

Niraj seems to be right, however it's not clear how the joint looks like. Osama, can you go to Appendix A, Fig. A-2 and say which sketch matches your joint? What is the tube diameter, wall thickness and tube pitch? What is your intended welding technique? I'm also guessing there are no grooves in the tubesheet hole, am I right?

Konrad,

1. Its a strength weld joint
2. Tube OD = 19.05 mm, 2.11 THK & Tube Pitch = 31.75 mm
3. Intended Welding Technique = GTAW
4. No grooves

I have checked Appendix A, Fig. A-2, my geometry match with Fig. 1 of Fig A-2.

Dear All,

Waiting for your assistance , Konrad.

Sorry, had to go away for a while.
Osama, does the bigger protrusion mean increased weld size, or is your weld leg length to be smaller than 5 mm? I mean, what is the purpose of increasing this standout: increased strength of the weld or simply having a longer stub protruding from the tubesheet? Does your client give any arguments? What are your arguments against it? Tube cost? Inconvenient length? Increased cost of welding?
Making a 3.5mm throat fillet weld on a 2mm thick member with TIG is kinda tricky, and it definitely doesn't increase the joint strength, because the tube is going to break prior to the weld anyway. Is there a fatigue issue anticipated in the HX? Any cyclic loading?

Yes bigger protrusion mean increased weld size. My client argument is to do the same welding with an automatic machine and their point of view is to do the same for ease in fabrication.

I dont know what is the limitation of an automatic welding machine? is it really practical or the code provide any margin for making a relatively longer stub protruding from the tubesheet ? Because i have read from ASME Section VIII Div 1 Appendix A, that 1.4 x a is the only basis.

You are right, the tube cost will increase as the total number of tubes are 2006 and the cost of welding will also be increased.

Konrad can you please tell me, how did you calculate 3.5 mm throat fillet weld size ?

There is no fatigue issue or cyclic loading i guess, because it a gas -gas exchanger i.e. process in tubes as well as in shell.

Waiting for your detailed reply, please. The matter is really urgent.

Osama,
Gas-gas sometimes means rapid transients, depending on the process (startups, shutdowns, instabilities, the process nature etc). Rapid transients mean high thermal stresses, usually concentrated in the tube-to-tubesheet joints, hence some people are tempted to increase strength of these welds, typically by increasing the size. Throat of 3.5 is 5mm leg length divided by 1.4 (give or take). If I was to guess, this could be a simple idea of mitigating possible fatigue risk- even if there is no real risk, the result of a leak may be disastrous, so in a typical risk analysis someone had to take some steps to do anything about it, just for the peace of mind. I'm afraid, without good understanding of the reason for increasing these welds, you don't have any sensible arguments for discussion. Why don't you contact the design engineer and possibly suggest other means, like proper expanding, prepping your holes to make a groove weld or something else.

Dear Dear,

I am afraid you underestimated me.

I am the designer. And while designing and with respect to the process conditions i have kept a strenght weld joint with a light expansion in order to avoid any leakage at tube to tubesheet joint.. Reference last posts.

So, please tell me as per your experience whether i may allow them or not ?

Konrad i think increasing throat size definetly increases the overall weight and eventually the cost. Also, the residual stresses is an issue.

Please conclude it Konrad

OSAMA,

As already highlighted by Konard, a throat size bigger than tube wall thickness is tricky and will not help in increasing strength.



From your earlier post it appears that client has specified this requirements for ease of fabrication, may be a requirement for some automatic orbital TIG welding machine for gripping purpose which is captured by your client based on their previous experience. To me, I do not see any other reason for higher protusion for the tubes.

SS

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

Interfering >>>
As per my experince :
If HX is veritcle we kept Top side of tube as flush and bottom side 5 mm Projection.
At that time i got answer is on bottom side free flow of liquid throguh tube without touching weld to avoid any residance of liquid on weld.

If it is Horizontal same principal for chemical designer --They want 5 mm projection To avoid any direct contact with weld and residance of that liquid with weld zone.

In case of vertical heat exchanger, flushing top side tubes is common to avoid any liquid accumulation on the tubesheet due to protrusion/ height of tubes.

Do not understand that how protrusion will prevent contact of fluid from weld as tube side will be full of liquid any way and liquid will be in contact with tube-tubesheet weld whether it is vertical or horizontal exchanger.

Osama,

Your client has only asked for 5 mm protrusion and that does not mean that you have to use even a higher weld throat. Isn't it better to ask your client itself the reason for a higher protrusion?