CONSTRUCTUAL QUERIES FOR PRESSURE VESSELS 2

[Elias141077]

Hi everybody.
Could somebody explain
1) why in most saddle supported horizontal pressure vessels one saddle has a sloted hole configuration and the other circular?
2) Is it permissible to weld a lifting lug beneath the welding line of a vertical elliptical top headed pressure vessel.?Please provide some standard dwgs if any.
3)For leg supported vertical vessel, with leg beams attached to shell in the diagonal axis how is it possible to perform painting in the small enclosed area between leg and shell (or leg pad) especially if you utilize top ...."rain"..plate cover for legs.?
4) Is it mandotory all external attachments of pressure vessels to be of the same material as shell?
5) Which is the ASME VIII code acceptable minimum clearence between 2 welds (i.e butt type)? If there is not a specific paragraph in the code are there any good engineering practices?
Thanks in advance.....

 

[TomBarsh]

I will answer "1". The vessel shell can "grow" in length due to thermal expansion (the vessel heats up and the material expands in length). If this expansion is restricted by the saddles being immovable, then compressive stresses will be set up in the shell, as well as bending the saddles. The slots and related details of construction are to permit the vessel to expand in length without the inducing the compressive stress.

Oh, for "4": No, this is not required. See UG-4(b) for more information.

 

[vesselfab]

1. thermal expansions

2. sure it is....that's the way most are done

3. you close it in with small plates to seal off the inaccessable areas

4. no mandatory. carbon steel vessels should have same P no attachments. alloy vessels should have alloy pads under carbon steel clips if large clips. we normally use alloy attachments just to keep from painting

5. we use 5t between butt welds. you can line up longitudinal seams if 100% radiographed

 

[Elias141077]

Thank you a lot..
Concerning first issue, what happens if the saddle wearplates are not welded to the shell.
Vesselfab could you please clarify the third issue?
Regards..

 

[boilerone]

Question 5 was answered before. But I want to add that instead of using such like several t's or D's, the rule for typical practice is ONLY that the heat-affected zones should not overlap. Even though, when overlapping cannot be avoided for the situation like, for example, longitudinal and circumferential weld intersections, you can deal with it by PWHT methods.

The original answer is here:

http://www.eng-tips.com/viewthread.cfm?qid=208212

 

[JohnGP]

If the saddle plates are not welded to the shell, then the shell will slide over the support as it expands. This is not an ideal situation as you potentially have a wear situation on a pressure retaining part that is easily avoided. You would also need some other means to restrain the vessel from vertical movement.

I thought vesselfab's response to the third issue was clear enough - if you have inaccessible spaces between the support and the shell, then you seal those spaces by filling the openings with welded plates. The thinking being that if they're sealed, then corrosion won't continue for very long, so you don't need to paint in there.

Cheers,
John