Using current stress values on an older vessel

[RNicastro]

I am inspecting a propane storage bullet which was built with "0" corr. allowance. Can I perform an "Alteration" to this vessel in order to recalc it using the latest stress values and give it some corrosion allowance? We just performed an internal visual inspection, magged the welds, and UT'd the shell. One of the courses is generally thinner and below the allowable min but it isn't corroded or pitted. I am comfortable with the ability of the vessel to do it's job but I would like to give it some flexibility. This vessel is in California.

Any help will be greatly appreciated.

 

[metengr]

I presume this is a pressure vessel fabricated in accordance with Section VIII, Div 1 of the ASME Boiler and Pressure Vessel Code. In lieu of alteration, the more appropriate question should be can you continue to operate the vessel because of this finding (thinner shell course). Correct?

If so, why not use API 579 and evaluate the vessel in terms of fitness for service? An alteration where no physical work is performed is indeed permitted by the 2001 Edition, 2003 Addendum of the National Board Inspection Code (NBIC) under RC-3024. However, you will most likely have to conduct a hydrostatic test of the vessel to meet the requirements for alteration.

 

[deanc]

Do you have the U-1? Do you have the orginal/year Construction Code? Suggest you perform calcs. to these. It was built to that code for a reason.

If you wish to seek something else see NBIC RB-9000 for a guide.

API or Alteration? Better ask the local Jurisdiction and the insurance carrier first.

 

[aclark]

I also suggest that you check with the local Jurisdiction, our State (Indiana)will not permit an alteration in the manner that you suggest.

 

[JStephen]

The changes in codes are not limited to allowable stresses. While you may wish to use a newer code with higher allowable stresses, it may also have more stringent requirements on testing, material selection, design temperatures, etc.

 

[jte]

RNicastro-

No, you may not alter the vessel by recalculating it using the new allowable stresses. Contact the State Pressure Vessel Unit at

http://www.dir.ca.gov/dosh/pressure.html

and ask them for a copy of Circular Letter PV-98-2 which deals with the application of Code Cases 2284 and 2290 (which lead to the new allowable stresses). The last paragraph in the letter is: "Finally, these Code Cases are for new construction only and the State of California will not entertain [their bold, not mine] the use of these Code Cases for a re-rate of existing equipment built to code rules using design factors of 4." That position has not changed. What the PVU will accept is new (replacement) components built to the current code like a replacment head, etc.

However, I agree with some of the above posts regarding API-579. This standard is nearing formal acceptance by the state (though it has been used by industry in CA for years). The gray zone I see with 579 is in the intent of its application. My approach (subject to change!) is that the intent of 579 is to get you through to the next planned downtime for a "proper" repair. So the longest interval you should have is to discover a problem during one downtime and FFS it 'till the next. Others consider a 579 FFS to be a more permanent solution.

jt