joint efficiency in the intermediate head attached to shell - UW-13

[saulook]

I have some doubts about the joint efficiency in the intermediate head attached to shell indicated in the FIG. UW-13.1(e). According UW-13(c)(2): "The butt weld and fillet weld shall be designed to take shear based on 1.1⁄2 times the maximum differential pressure that can exist. The allowable stress value for the butt weld shall be 70% of the stress value for the vessel material and that of the fillet 55%."

1-I need calculated the head thickness using P=1.1/2 times the differential pressure and E=0.55 and the shell thickness using P=1.1/2 times the differential pressure and E=0.7?

2-It´s possible X-rayed fillet weld? Because in the table TABLE UW-12 indicate "Degree of Radiographic Examination" "NA"
If possible, when I use X-rayed 100% on the fillet weld and fillet weld can I used E=1?

 

[SnTMan]

saulook, joint efficiency per UW-12 is not applicable in this joint.

1) Calculate head thickness (as a seamless head or not, as applicable, E = what it equals) per UG-32 and UG-33, based on max differential P that can exist and which direction. Calculate shell thickness per UG-27 and UG-28, if applicable, using E as appropriate for seamless, Spot or Full RT of the long seam. Now size the two welds per UW-13(c). Capacities for each are given, each contributes its portion to the 1 1/2 dP requirement.

2) No, not likely. Fillet welds are generally considered non-radiographical, and use E=1 when needed. See Table UW-12 Type (7) & Note 5.

Regards,

Mike

 

[saulook]

But how can I design this welds? Where do I use the 55% and 75% of the stress material?
I´m studing a calculation sheet and the designer calculated the shell using E=0.55 and the head E=1. It´s correct? The weld calculation shall not be provided in the calculation sheet?

Thanks.

 

[chicopee]

In pressure vessels a tapered welded joint having a 3:1 ratio will have an E=1.

 

[SnTMan]

saulook, doesn't sound correct to me. For Butt weld: Weld strength = circumferential length of weld * root opening * minimum of (So,shell or head) * 0.7. For Fillet weld: Weld strength = circumferential length of weld * minimum leg * minimum of (So,shell or head) * 0.55. Total weld strength = sum of the two. Total weld strength shall be >= to 1 1/2 dP.

Using E = 1 for the head is probably right if the head is seamless. Using E = 0.55 for the shell implies to me it is lap welded. Yes / no?

Regards,

Mike

 

[saulook]

The intermediate head is seamless and calculated per UG-32 (E=1). The shell is calculated per UG-27 (E=0.55) and the joint is a butt weld joint and not a lap joint.

The drawing is identical the sketch UW 13.1-(e). The required thickness for internal pressure is 6mm for external pressure 10mm and the actual thickness indicate in the drawing is 30mm. I think that the designer use this thickness, probable, for the weld strength, but nowhere in the calculation sheet it´s show the weld calculation.
Thank´s Mike for your explanation and pacience...

Regards,

Saulo.

 

[SnTMan]

saulook, about your cylinder thickness: there are two calculations that can be made, one for circumferential stress (or thickness), one for longitudinal stress. Each can be performed with a joint efficiency appropriate to it. Normally the circumferential stress formula will govern. See Note 16 of UG-27. So for this case, I would think the following applies:

Roll and weld cylinder, spot RT of the long seam, E = 0.85. Required thickness for circumferential stress per UG-27(c)(1) = t(c).
Circumferential seam E = 0.55, as per UW-13(e), required thickness for longitudinal stress per UG-27(c)(2) = t(l)

Required thickness of the cylinder is greater of t(c) or t(l). Is this perhaps what your designer is doing?

I would think in this case, circ stress would govern as it most often does as 0.55 / 0.85 = 0.65, greater than 1/2.

Regards,

Mike