Isolation blind thickness for hydro test

[mechengr12]

During the shutdown I am planning on performing a hydro test on an exchanger and must install two blinds. These will be temporary and will not hold pressure for long. History reports noted that the spacing between flanges was to thin to meet ASME B31.3 blank calculations for thickness. The pipe is 26" carbon steel and will be tested at 90psig at 80degF with water. Allowable stress of a A-105 blind is 23.3ksi, but is it possible to use the tensile or yield stresses since deformation of the blind is acceptable (but not probably). Calculations come out to 0.69" for 90psig for me, and 0.49" for 45psig. I would like to pressure up to 90psig, but want to check with some others on thoughts of putting a 0.5" thick blank in and pressuring up to 90psig at 80degF.

 

[IFRs]

Try a different material with greater strength?

 

[racookpe1978]

What schedule 20 inch pipe?

A 20 inch dia flange is large, but 90 psig is relatively low.

1. You can back-flood the other end of the pipe to a modest pressure (use you your operating pressure of 45 psig for example) so the differential pressure across the large flange is not 90 psig, but 45 psid.

2. I am very, very surprised you are not able to move the flange apart by another 1/8 inch to get the thicker flange in position. Try again. Pipes and equipment are really very mobile once supports are loosened during maintenance.

 

[TGS4]

This exact topic was was covered in an ASME JPVT paper (published 9 years ago - 10 years ago if you count the ASME PVP paper that this Journal article was based on):

http://pressurevesseltech.asmedigit.../article.aspx?articleid=1459628&resultClick=3

It is possible to undersize slip blinds - BUT you need to ensure that the deformation is small enough that you can remove the deformed blind after application of the pressure.