Adding Duplicate Nozzle to Existing Vessel with a Lower Allowable Stress - Repair?

[AWDMIKE]

We are planning on installing a new LWN nozzle in an existing vessel. The new nozzle will be a duplicate of an existing nozzle and will be installed at approximately the same elevation of that existing nozzle (i.e. same shell course). This new nozzle is not replacing an existing nozzle. We are hoping to classify the addition of the new nozzle as a repair.

While this is similar to a previous post of mine, this work is a little different. Here is a summary of strengths and allowable stress at 1050 F:
Original Material............New Material
SA-182-F11...................SA-182-F11-CL2
Yield = 40 ksi................Yield = 40 ksi
Ultimate = 70 ksi...........Ultimate = 70 ksi
Allow.Tens. = 5.5 ksi.....Allow.Tens = 4.2 ksi

Unusually, the allowable stress in tension for the material appears to have decreased since 1971.

Is there any chance of classifying this as a repair? I have reviewed NBIC Part 3 and while it discusses an increase in allowable stress, there is no mention of situations where there is a decrease in allowable stress.

My experience is telling me this is going to be an alteration.

Thanks for any help or guidance anyone can offer. We are using the NBIC for this work.

 

[metengr]

It would be an alteration because the wall thickness will be different (thicker) from the original design wall thickness. If the allowable stress would have increased, it could be a repair provided the wall thickness remained as original, in other words you cannot take credit for thinner material.

 

[AWDMIKE]

Metengr - Thanks for the quick response on both of my recent posts. I had thought of that and should have mentioned in my original post that the original nozzle may have been oversized and we may be in a situation where our new required thickness is still within the duplicate nozzle. We need to run the numbers for that still.