Spectacle Bilnds

[pipe15]

is it more common to have spectacle blinds made from plate or have them forged. We have some that are 16" Class 600. Also, what about a raised face or not?
thanks
mark

 

[europipe]

raised face?

Here's what we use to make.

Greetings

 

[pipe15]

I noticed the sheet you sent says not to use them for hydrostatic testing. Why is that?
thanks again
mark

 

[europipe]

Should they be different?
And why then?

 

[Cuemaster64]

Gentlemen,

It is my understanding that spec blinds are not to be used for hydros for the distinct purpose that they might not meet the flange ratings of testing. Thicknesses of spec blinds are not the same as testing blinds. Spec blinds are used for blanking off lines for work down stream of lines. Maybe this will answer some things. Correct me if I am wrong.

Eric

 

[jte]

Well, you could adopt ASME B16.48 as your line blank (a.k.a. "slip blind") standard. It includes Figure-8 Blanks (a.k.a. spectacle blinds). It is one of the referenced standards in B31.3, so legal for use in B31.3 systems. The design is based on B31.3-2002 (see the Foreword). Cheap at $58.

http://catalog.asme.org/Codes/PrintBook/B1648_2005_Line_Blanks.cfm

If you go by that standard then acceptable materials are per B16.5 Table 1A which includes plate materials.

From 3.3.1, A raised face may be specified at the option of the purchaser.

Ratings are per B16.5. As for hydrotesting, 2.2.2 states that Line blanks may be subjected to system tests at a pressure not to exceed 1.5 times the 38°C (100°F) rating rounded off to the next higher 1 bar (25 psi) increment... So it would appear that the blinds (if B16.48 compliant) are considered to be adequate for hydrotests.

jt

 

[europipe]

Eric,
Spectacle blinds are calculated and used for full press.requirements and spades are used for seperations of systems for whatever reasons.

Greetings

 

[pipe15]

Thanks for all the info. This is a bit of a strange situation.

This spectacle blind is in a 16" line and is a Class 600 system. It is part of a depressurization system and the blind is used only for hydro-testing purposes. Seems like an expensive setup (2 16"CL600 stainless RFWN flanges, hardware, and the blind) for just a single use.

 

[PAN]

pipe15,
You may calculate to use carbon steel plate for hydrostatic test.

 

[unclesyd]

You don't need to make a blind as you can rent one. Also it you need some blind flanges they are for rent too.
Here are 2 of several places that rent blinds and flanges.

http://www.usaindustries.com/pipe_blinds.htm#spectacleblinds

http://www.twincoindustrial.com/blinds.html

 

[Giuss]

Pipe 15,
even if cost difference beetween Paddle Blinds Forged and those made from Plate is very variable and not so high as you could expect, basically i'll say: it's most common to specify them form plate.
Otherwise, if your blanks are in CS on services which could cause severe stress corrosion cracking and/or Hydrogen Induced Cracking my advice is to specify forged blanks, in this sense, you have to consider that a blank made from a plate HIC tested is much more expensive than a forged one.

Bye

Giuss