Modifications to B31.3 Piping w/ Overstress

Modifications are being developed to 450 psig superheated steam piping. Stress modeling of existing pressure reducing station that is within the scope of the piping receiving the planned modifications indicates expansion stresses are 7 times and occasional stresses are 9 times above the allowable stresses in portions of the station. The modeling is based on B31.3-2004 code (in a chem/pharm plant). System has been in operation for about 10 years. Piping is SA-106B.

My understand is that just because the piping has held up for 10 years does not mean the piping is okay, rather, due to the extent of the piping showing overstress I am advising corrective modifications be implemented at the reducing station as well as at the location of the planned modifications.

I am first going to look at whether restraint modifications alone will reduce the stresses to below allowable stresses (doubtful). But I'm thinking ahead to making modifications.

1. Concerned about the fatigue stress that is resident in the existing piping, it seems prudent to not simply make restraint or piping modifications that reduce the stress, but to demo the piping that is shown with expansion overstress. Comments?
2. It also seem prudent to remove the piping that is indicated as overstressed by occasional loads too unless it can be established that occasional loads have not occurred. Comments?

Ken A. Nisly-Nagele, P.E.

Project Engineer, Mechanical

Applied Engineering Services, Inc.

7999 Knue Road

Indianapolis, IN 46250

317-585-8920

[Non-text portions of this message have been removed] Received on Fri Feb 24 11:32:00 2006