Sight glass - special design per ASME VIII Div 1

[MikeG7]

Hi All
Is there any advice how to go about the design of a custom inpsection nozzle with a sight glass. The glass is sealed with a gasket . The picture shows a similar item to the one in question. The only difference is this one has few bolts keeping the glass cover in place. The one I want to design - the cover has a thread.
According to me, this is included in the scope of the Code ASME VIII Div 1, but no readily available formulas are at my disposal to attend to such a design. I would like to ideally not have to undertake FEA unless very necessary because the thread can get quite complicated to mesh and solve and categorize in terms of stress (according to ASME)
What about the piece of glass? Is it necssary to "design" it to ensure that it is safe or is that taken care of in the pressure test proecess?

Michael

 

[SnTMan]

MikeG7, there are no specific rules for the design of these things in Sec VIII, Div. 1. This would fall under U-2(g) and good engineering practices.

Gasket: adapt methods of Appendix 2 to develop loads for seating and sealing. Threaded cover: design as per ordinary screw thread design, see Machinery's Handbook, for example. Opening in the vessel: design per UG-37 principles. Glass: here is the real problem, you may get some design methods from glass manufacturers or other open literature. Worst case, proof test it.

I'd make the observation that these things existed long before FEA techniques were available.

Can you just buy one?

Regards,

Mike



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

 

[MikeG7]

I maybe could get my client to get something that is pre-approved (ASME approved).
Thanks I will give these design procedures another look and maybe try and do what is reasonable to meet Code requirements
;-)

 

[XL83NL]

This topic may provide some further leads.
based on the interpretations provided, and other topics on eng-tips here, it seems logic that only the welded-in metal part, that creates a sealing with the glass, has to follow ASME VIII-1 requirements.

 

[r6155]

See DIN 28120

Regards
r6155

 

[MikeG7]

Thanks R1655,
being "DIN" will the material be acceptable under ASME code? I often have an issue when I find a material under another standard and I cannot find a hot allowable strength in ASME to check the bolts, flange, etc.

 

[r6155]

MikeG7. DIN 28120 is only a guide for you, search any supplier according to ASME.

Regards
r6155

 

[SnTMan]

It is true that the bulk of the sight glass assembly need not meet ASME requirements, it is also true that it need not be hydro'd, although it will obviously be leak-tested at some point.

But if the OP is going to "roll his own" then there needs to be some design work, some paper trail, something, that shows the assembly is good for the relevant design conditions.

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

 

[MikeG7]

SnTman you say "need not meet ASME requirements" , but please U-1(e)(3) - covers are in Scope of ASME. Is it that you were saying that they are not required to meet ASME requirements, or that inherently it is difficult to achieve compliance?

 

[SnTMan]

MikeG7, strictly speaking, any part of this assembly not permanently attached to the vessel could be considered out of the scope as per U-1(e)(1)(d) or U-1(e)(4). It is likewise obvious the glass itself is not a Sec VIII, Div 1 material, nor are gaskets.

Still, the assembly has to be shown, in some fashion, to be suitable for the service. This can be a manufacturers' rating for bought parts or a fabricators' design documents for custom parts.

Regards,

Mike

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

 

[MikeG7]

Hi SnTman
The covers and bolts are not "permanently attached to the vessel" but are definitely included in the scope. I know this is symantics but I can't see how the removable parts can be excluded when reading per U-1(e)(3).
U-1(e)(4) as you point out does offer some relief on the glass

This takes me to your second point that it has to be shown to comply. I was hoping to hear how others have approached similar problem

 

[SnTMan]

OK, I've never designed one of these things, but:

Practically, the metallic parts can be Code materials as easily as not. Div 1 rules can be followed where they exist, good engineering practice where they do not. Gaskets / seals, pick what you like. I still think the hard part is the glass, properties not known, design formulae uncertain. Maybe buy a rated glass, maybe buy the whole thing.

Talk to your AI early in the process...

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

 

[MikeG7]

Thanks for your input SnTman

 

[DriveMeNuts]

The housing, threads and bolts are as per the code.

For the sealing arrangement there is a code published by ASME called ASME PVHO-1. It relates to acrylic viewports for human occupancy.

Much of its methodology will also apply to the design of glass viewports. It includes requirements for design margins and material verification.

 

[r6155]

Use same formula for blind disc with the properties of glass.
As a guide, see AD 2000 Merkblatt -Pressure Vessel made of Glass. Permissible stress for borosilicate glass is 6 N / mm2 by tensile and bending.

Regards
r6155

 

[r6155]

More information

http://www.maxmuellerag.com/media/en/VETROLUX DIN 28120 28121.pdf

http://glassproperties.com/references/MechPropHandouts.pdf

Regards
r6155