Nozzle on blind weld detail

[mohsenmaleki]

Dear all,
Thanks in advance for your kind reply,
Our client's specification states for welding joint full penetration shall be considered.
So, problem is:
A) Can we carry out SET-ON instead of SET-IN(see attachment) for welding nozzle on blind flange?
B) In cyclic loading set on weld detail (see attachment)is applicable or not?
Regards,
Mohsen Maleki

 

[Dhurjati Sen]

Mohsen Maleki

The answer would depend on the design parameters (like pressure and temperature)& service (like lethal or non-lethal).

 

[mohsenmaleki]

Dear Dhurjati Sen
For more information,
Pressure: 22 barg
Temperature: 315 C
There is also cyclic loading.
Service: Non-lethal
Regards,
Mohsen

 

[mk3223]

IMO, it's not a good practice to use stub-in connection, either stub-in or stub-on connections, in a cyclical service without reinforcement. Consider to use the sockolet for the branch connection instead of stub-in, and add the steel branding, as needed, to mitigate the vibration issue.

 

[SnTMan]

mohsenmaleki, in general a set-in detail is preferred, because it is possible to truly double-weld it. However, if the shell component (the blind, in your case) is very thick, a set-on detail may be acceptable given proper weld techniques. If done correctly, either detail is a full-penetration weld.

Client specs can restrict the use of set-on details. I am not sure either detail has an advantage for cyclic service. By "cyclic loading" do you mean cyclic external loads? Or cyclic pressure/temperature loadings?

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[r6155]

mohsenmaleki

Reply A): yes
Reply B): is applicable

Nozzles can be of the set on type, but welding can be difficult or create problems such as lamellar tearing.
Design of the juncture of the two parts is a major consideration in reducing discontinuity stresses. Fillet weld shall be machined to suitable radius.
Although it is not possible to eliminate all stress risers and concentrations, some design details to be avoided are as
follows;
1. Use integral construction
2. Avoid fillet welds for attachments to pressure boundary
3. Avoid reinforcing pads
4. Avoid threaded connections
5. Avoid partial penetration welds
6. Avoid stud bolt connections
7. Avoid leg supports

Is a good engineering practice to use set-on nozzle and reduce the amount of welding material.

Regards
r6155

 

[mohsenmaleki]

Dear SnTMan,

Cyclic loading is eventuated from cyclic pressure and temperature.

Regards,
Mohsen

 

[mohsenmaleki]

Dear r6155

What is your opinion for external attachment such as trunnion, insulation support, ladder and platform clips and etc.
All of them are attached by fillet weld.

Regards,
Mohsen

 

[r6155]

mohsenmaleki
Please, see Pressure Vessel Design Manual 4th edit, by D. Moss.

Regards
r6155

 

[TGS4]

If you have cyclic temperature and pressure, then it is poor design practice to attach any external attachments, especially by fillet welds. Regardless, please ensure that the manufacturer performs the necessary calculations to demonstrate the adequacy of any design for the cyclic conditions (i'm referring to fatigue calculations here).

 

[r6155]

mohsenmaleki
My opinion: instead of fillet weld use full penetration weld + fillet weld and ground smooth or contoured.
Try to reduce the number of attachments (internal and external)

Regards
r6155

 

[mohsenmaleki]

Dear
Dhurjati Sen
mk3223
SnTMan
TGS4
Kindly, I appreciate for your reply.

Regards,
M.Maleki

 

[fabineer]

Assuming the larger and smaller flanges are standard sizes, a standard Reducing Flange (250 DN/10" to 80 DN/3" or similar) is a often simple but robust solution. The only weld required then would be two circular seams for pipe to reducing flange and pipe to smaller flange. Similar to below.

It would likely help with the fatigue design as well since it will have less sharp corners compared to your sketches.