Fillet weld size for a thinner nozzle. Manufacturing problems?

[Farid44]

I have been working on standardizing headers for boilers . one of the most important issue is the fillet weld size for tubes of 4mm thick.
->an example is for a 200 NB pipe of lets say SCH 120 I am going to have tubes of 63.5 mm OD at a spacing of 101.9. I have calculated the pipe thickness based on ligament efficiency. The tubes are kind of set on on the header pipe with a some depth for groove 6mm and the fillet weld size as per some old standard is 9mm(6mm throat size).
The Questions are:
1) is it practical to have a 9mm fillet weld with a groove of 6 mm deep for a tube thickness of 4mm.
2) do we need to do weld strenght calculation as we do for tubes in tubesheet of heat exchanger (full strengtt welded,partial strenght welded), which I think if I am not wrong refers to the stenght based on tube, full strength weld mean that if tube is pull the tube will fail but the joint won,t get failed? am I right as per this understanding?
3) considering the pipe thickness is based on ligament efficiency , do we need to do the weld strenght calcualtions as mentioned in ASME SEC VIII DIV 1 or ASME I where weld strength required is based on area required fo rreinforcement.

Please suggest ..too much confusion on my side..
Thanks

 

[boilerone]

Farid44,

Assuming your header is for ASME Sec I boiler application, my answers are:

1) Yes, 9mm fillet weld is practical.
2) Per Sec I PW-15.1.6, weld strength calc is not required if your design conforms with certain figures in Fig. PW-16.1. From your description your design matches type (z) and it is exempted of strength calc.
3) If your pipe thk. is calculated and determined from ligament efficiency (only) then you do not need do header strength reinforcement calculation for the tube openings BUT make sure that in your ligament efficiency (the E value) calc, you are taking into consideration of the 6 mm deep tube seat which has a larger dia. than the through hole on the header. An 'average tube hole dia.' other than the through hole dai. should used in the E value calc.

Boilerone

 

[Fizza453]

Farid,

In your case, in addition to PW-15.1.6, PG-37.4(b) also expemts weld strength calculations of PW-15.
In your case, weld size shall be 4 mm minimum (leg size) in order to meet the requirements of PW-16.
For tube to tubesheet joint (as your case is), we take extra care by meeting the requirements of QW-193, QW-288 and QW-303.5 of Section IX although it is not a mandatory requirement of Section I.
There is no definition in Section I of full or partial strength welded tubes as you see in UW-20 of Section VIII-1.There is no qualification rules in Section I for the tubes which are neither full strength welded nor partial strength welded, such rules are contained in Appendix A of Section VIII-1.

Section I only recognizes 'strength-welded tubes' if you see PG-27.4.4 and A-317.3(f). Unfortunately, there is nowhere defined in Section I what 'strength-welded tubes' are?. Fortunately, you will see the definition of 'strength-welded tubes' in 2011 addenda of Section I.

Hope it helps a little.

Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[unclesyd]

If there is any confusion concerning the weld on your header you might want to consider an extruded header that changes the weld detail to a butt weld, that can be readily inspected.
The cost of the headers with butt welding will more than cover the cost of your fabrication cost.

http://www.osiforge.com/JobPictures.html

http://www.sivcoinc.com/extrusions.htm

http://www.weldfit.com/extruded-outlet-headers-manifolds.html

 

[Farid44]

Hi,
Many thanks for your valuable feedback in this regard. Nasir, Boilerone, uncelsyd... much appreciated for your response in this regard... Thanks