Reason for Unusually High Hydrotest Pressure on Older Pressure Vessel? 5

[Christine74]

I've noticed that pressure vessels built in the 1940s and 1950s were often shop-hydrotested at pressures much higher than 1.5X (now 1.3X) required by the Code and was curious to understand why. Some vessels that were carbon steel construction with design temperatures below 650 F (temperature correction factor = 1.0) were hydrotested at more than 2X the listed MAWP. This applies to ASME Section VIII (there were no Divisions I/II/III yet) as well as API-ASME pressure vessels.

Were the higher hydrotest pressures due to special Code requirements in place at the time or was it just a common industry practice during that period?

Thanks.

-Christine

 

[gr2vessels]

I believe the reason was the test pressure was based on MAPNC, not the MAWP. In other words, the safe 'over-design' at that time allowed for much higher MAP than MAWP. Normally, we use today the UG-99 based on UG-99(b) or (c) and footnote [34], thus allowing the 'safe' rating of the vessel much lower than paid for, but conveniently low for the fabricator. My two cents...
Cheers,
gr2vessels

 

[macmet]

We build boilers under ASME Section 1 and our hydrotest pressure is more than 1.5x the MAWP. We use the definition it must be 1.5x (I think 1.5?) times the highest working pressure in the system. Our units have a high feedwater pressure and that often dictates what our hydrotest pressure is.

I'm not sure if that is relevant to you or not.

 

[marty007]

Do you have any very strange geometry in your vessel? If so, is it possible this was related to a proof test (UG-101)?

 

[doct9960]

Christine,

The higher hydrotest pressures were due to the Code requirements in place at that time. Some of the vessels in the 1940's were hydrostatically tested to at least twice the MAWP. Check out Paragraph U-77 on page 77 of the ASME Section VIII 1943 Edition...

https://law.resource.org/pub/us/cfr/ibr/002/asme.upv.1943.pdf

 

[SnTMan]

doct9960, excellent!