PV de-rating 10

[raduval]

We are running some 30+ year old PV (VIII-1). One of them is getting thin (shell thickness under min. value for MAWP)> I 'm thinking about de-rating the vessel to a lower MAWP.
How do I go about doing this ?
Your help would be greatly appreciated !!

 

[aclark]

For your information, the Stae of Indiana does not permit either.

 

[solinar]

In my opinion, API-579 is not presented as a short term stopgap to last you until the next outtage.

The Foreword of API-579 contains the following sentence:

"This publication is intended to supplement and augment the requirements in API 510, API 570 and API 653: (i) to ensure safety of plant personnel and the public while older equipment continues to operate; (ii) to provide technically sound fitness-for-service assessment procedures to ensure that different service providers furnish consistent life predictions; and (iii)to help optimize maintenance and operation of existing facilities, maintain availability of older plants, and enhance the long-term economic viability."

The term "life predictions" says to me that 579 is intended to be used as a method to predict what the remaining life of a piece of equipment might be, whether that is 2 months to the next outtage or 30 years.

The phrase "enhance the long-term economic viability" also seems to state that the methods in this document can be used to support the usage of equipment over a long period of time.

I completely agree that the first step is to check with your jurisdiction to see what methods or documents they allow for rerating.

 

[oldygoldy]

Solinar is absolutely correct. API 579 also specifies methods for monitoring where applicable. You can continue unless other defects are found as in normal case. Of course many users will do the repair or replacement, if it is not difficlut, at the next opportunity.
The most important benefit of API 579 as per me is "--- to ensure that different service providers furnish consistent life predictions;" Each type of defect and how to assess is detailed in 579. Now the user can ensure that standard methods are used by specifying API 579 for FFS and can be confident of FFS result.
Remember- 'Factor of safety is factor of uncertainty'!

 

[chicopee]

pipesnpumps- AIA will not allow you to rerate (upward) ASME/NB vessels since their fabrication was performed in accordance to ASME code dated at the time of fabrication. But AIA will allow you to derate as long as some of the comments by above contributors are met. Also any major repair and calculations perform on such vessel will have to be done by that same code used at the time of fabrication.