Location of Skirt attachment to the vessel 1

[oldisgold981]

Hello
I want to know when to use which kind of attachment.
Skirt can be attached(welded) to the vessel in the followings ways.
1. Skirt can be welded directly to the bottom of the head.
2. Skirt can be attached to the inside diameter of the shell, upto the tangent line.

3.Skirt can be attached to the outside diameter of the shell (id of the skirt is at the od of the vessel)
My question is,is there any guideline when to use which of the above attachment?.
What are factors that determine to use which configuration.

 

[r6155]

Your description is not coincident with the sketch.

Regards

 

[JStephen]

I like the middle figure myself.
The left figure induces some bending into the head for no real benefit.
Actual welds might vary.

 

[oldisgold981]

@TGS4
Can you please share your feedback about it which skirt to head configuratiin shall be used when?

 

[Some Curious Guy]

The skirt attachment detail depends on reaction loads , local stresses at the skirt to shell-dishedend junction and the thermal gradient stresses between skirt and Shell-dishedend. Actually there are no thumb rules here and we have to use our judgement every time. Try to get a feel of distortion at the skirt junction due to mean dia misalignment, differential expansion due to temperature and loads and then decide which detail is most suitable.
Description no 2 is more popular because the skirt mean dia and the shell mean dia are almost coincident and it introduces less localized stress. We mostly use this when the shell is thicker than skirt but I have seen it for even low pressure and low temperature application. This is simply the more robust detail and people use it to simply play it safe.
Description no. 3 can be used for low pressure, low temperature application and for relatives light weight equipment.
Avoid using description 1 for reasons mentioned by @JStephen above.

 

[r6155]

1) For small PVs, usually only with external fillet weld.
2) Best design for most PV. Do not use when high quality (RT or UT) is required at the junction with the head.
3) Poor design. Inspection of the shell under the skirt is impossible. Avoid this design. Never use it for low or high temperatures.

Regards

 

[TGS4]

I concur with r6155's assessment. Larger and/or hotter vessels, especially those in cyclic service, may require a forging instead of a weld.

 

[oldisgold981]

Thank you all for your help.