I design ob-round sight glass installed on vessel shell and cal FEA, result show very high von-mise. 1

[pv_mkk]

Vessel info :
-Design as per ASME Sec.VIII Div.1
-SS304
-Shell 12mm ; 3500mm TL-TL; ID2500mm
-Ellip Head 12mm
-Vertical
-D.P. @6Bar/FV ; Test P. @7.8Bar

Sight glass base frame is designed following sight glass vendor's catalog by using model that can retain pressure to 10Bar.
And I also increase thickness from the catalog.

Sight glass arrangement as you see in the picture below.

But FEA result showed that at sharp edge of round corner of sight glass base frame has stress around 600-700MPa and deformation occured around 2.5mm

Can I still fabricate this vessel from this design?

Or I cannot use this sight glass model from this vendor?

Please kindly suggest. I never designed this kind of sight glass before. How can I make sure to my customer that the design is safe.

Thank you very much.

 

[racookpe1978]

OK, try this.

You have a long (tall) sightglass, and have mentioned a problem with significant plugging (contamination and deposits) inside the sightglasses on earlier Pressure vessels so you do NOT want to use small single-drilled holes at the top and bottom of each sightglass in the group of 10.

But, you are essentially cutting long narrow "slots" in the wall of your pressure vessel. Under internal pressure, the tank walls want to expand out, but are restrained - everywhere BUT these long tall slots - by the PV walls.

At the midpoint of each of the ten slots, each side wall bends out and away, and pulls the sightglass frame away from its restraining weld at and across the curve of each end. At the midpoint of the sightglass "loop" you should also see bending and compression extremes as well - they are not shown in the photo above.

So. To fix.

Drill 2x shorter slots (or 4x drilled round holes) to match the top and bottom point of each sightglass, plus a margin to prevent deposits from plugging the hole. The "middle" of the sightglass then has a thick section of basemetal remaining across the previous slot that will restrain the opening force now trying to separate both sides and tear the PV wall in two. Hence, not quite half the stress, but probably 3/4 or 2/3 the original stress at both tips.