Standardising Spectacle Blind Material

[davet1948]

I have been reviewing the MRO Spare Parts Listing for Spectacle Blinds for an oil & gas operator. They have 8 different stock nos for 3/4" 150# blinds. The range may have been deliberate or most likely "as supplied" on different projects over the years.
BLIND,SPECTCL,3/4",150#,5MM,SS316,FF
BLIND,SPECTCL,3/4",150#,5MM,SS321/347,FF
BLIND,SPECTCL,3/4",150#,5MM,GR60,FF,SR
BLIND,SPECTCL,3/4",150#,5MM,CS,GR60,FF,SR
BLIND,SPECTCL,3/4",150#,5MM,CS,GR60,FF
BLIND,SPECTCL,3/4",150#,6MM,A516/GR70,FF
BLIND,SPECTCL,3/4",150#,6MM,CS,FF
BLIND,SPECTCL,3/4",150#,5MM,S31803,FF

I think SR indicates a coated blind

The table I have shows 3mm thickness for a 3/4" 150# class blind, where has 5 & 6mm come from?

I am sure there is scope to reduce the range stocked, any suggestions??

Appreciate any members comments

 

[LittleInch]

My guess is that these all came from different piping specs and include a nominal corrosion allowance of 2 or 3mm.

The service of each of them may result in some being CS and others Stl Stl as blinds like this can easily come into direct contact with the fluid and of course when open will have the inner surface exposed constantly to the process fluid. The open part has an effective wall thickness of 16.5mm which seems very thick for a 3/4" pipe.

As to which material? Given the possible ranges of fluids one of the Stl stls would seem to be a good choice.

Also check out the min design temp of the systems. all the CS ones look like they could be combined, the Stl Stls not so sure about.





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[TugboatEng]

You need to find a material that will exceed all requirements. In all cases. You have some specialized alloys in there. The 318 stainless steel would be used for severely corrosive service where the 321 and 347 stainless steels would be used for high temperature service. For a catch-all material, you're likely going to want to use an inconel alloy such as 825.

Is that going to be worth the cost? Otherwise, you could probably cover all of your carbon steel bases with the A516 material. Another option would be to replace all materials with the 347 stainless except for the 318.

Your next problem is handling the different thicknesses. If you can determine that the 5 mm thickness is acceptable for all cases, you may be able to use different thickness gaskets to make up the difference.