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PV de-rating 10
- Thread starter raduval
- Start date
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First off, I would contact your Inspector or Authorized Inspection Agency that insures the vessel and contact your Jurisdiction to inform them of your intentions to permanently de-rate the vessel.
Typically, an in-service pressure vessel falls under the domain of the National Board Inspection Code (NBIC). A de-rating of MAWP would fall under the definition of an alteration (see Appendix 4).
In any case, I would expect that the Jurisdiction will provide specific guidance in requirements for stamping a new nameplate with the lower MAWP. I would expect that some type of engineering analysis will be required by the Jurisdiction to determine the cause of the wall thinning, and justification of the de-rated MAWP. I would expect you will have to ultrasonically test the vessel wall thickness and perform a hydrotest at 1.5 X (derated MAWP).
Typically, an in-service pressure vessel falls under the domain of the National Board Inspection Code (NBIC). A de-rating of MAWP would fall under the definition of an alteration (see Appendix 4).
In any case, I would expect that the Jurisdiction will provide specific guidance in requirements for stamping a new nameplate with the lower MAWP. I would expect that some type of engineering analysis will be required by the Jurisdiction to determine the cause of the wall thinning, and justification of the de-rated MAWP. I would expect you will have to ultrasonically test the vessel wall thickness and perform a hydrotest at 1.5 X (derated MAWP).
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raduval,
API 579 allows you to assess defects on pressurised components (Fitness for service) to check whether they may be still used at the original conditions. Also there are provisions to re-rate the components if they fail in the assessment. It covers ASME VIII and the piping Codes. That's the way to go!!
API 579 allows you to assess defects on pressurised components (Fitness for service) to check whether they may be still used at the original conditions. Also there are provisions to re-rate the components if they fail in the assessment. It covers ASME VIII and the piping Codes. That's the way to go!!
When you contact the AIA they will most probably require recalculation of entire vessel wall thickness and don't forget about the nozzle reinforcement calcs.
The AIA should also tell you which code to use and to what extent. API 579 is good for assessment of localised defects if you have them. For general corrosion such an assessment might not be necessary. It is always good to find a cause of corrosion before rerating and try to mitigate it to extend the life of equipment.
The AIA should also tell you which code to use and to what extent. API 579 is good for assessment of localised defects if you have them. For general corrosion such an assessment might not be necessary. It is always good to find a cause of corrosion before rerating and try to mitigate it to extend the life of equipment.
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raduval,
When rerating/derating a pressure vessel you should contact your Jurisdiction to find the proper code to use (NBIC or API)for the the rerate/dererate. It also will help to have the original code and year of construction. I spend most of my time rerating pressure vessels and I have most all of the old ASME Sec VIII books. So if I can be of any help to you let me know.
QA Scott
When rerating/derating a pressure vessel you should contact your Jurisdiction to find the proper code to use (NBIC or API)for the the rerate/dererate. It also will help to have the original code and year of construction. I spend most of my time rerating pressure vessels and I have most all of the old ASME Sec VIII books. So if I can be of any help to you let me know.
QA Scott
pipesnpumps
Mechanical
QAScott,
I would like to check an existing vessel to see if it was conservatively designed and can be rerated for a slightly higher pressure.
This is a 40 yr old vessel, but hasn't used half the corrosion allowance. I think I know what the answer will be, but let me ask anyway - What procedure is best for evaluating a rerate?
I am assuming the calculation needs to be based on the Section VIII code for the year it was built, but will a calc based on current code be accepted?
Would it be acceptable to reduce the corrosion allowance to the difference between the minimum surveyed thickness and the original fully corroded thickness?
pipesnpumps,
What rerate code will you be using NBIC or API 510? This wiil help me address the issue of what ASME Sec VIII edition to use for this rerate. You can reduce the corrosion allowance as needed for this rerate to get the out come you are looking for. Just do not forget to address all loading on this vessel when doing the rerate.
QAScott
What rerate code will you be using NBIC or API 510? This wiil help me address the issue of what ASME Sec VIII edition to use for this rerate. You can reduce the corrosion allowance as needed for this rerate to get the out come you are looking for. Just do not forget to address all loading on this vessel when doing the rerate.
QAScott
pipesnpumps-
Most jurisdictions will accept calc's based on the original code of construction, either the original edition or the latest edition. In fact, I believe there's an NBIC interpretation out there somewhere that says so; I don't have the time now to track it down. So chances are you can use VIII-1, 2001 A03. Trick question: How do you know your vessel was built to Div. 1? Just use the allowable stress from the original edition of the code of construction. Hopefully you have a copy of the original code. If not, post the material and temperature and I can get you the allowable stress.
jt
Most jurisdictions will accept calc's based on the original code of construction, either the original edition or the latest edition. In fact, I believe there's an NBIC interpretation out there somewhere that says so; I don't have the time now to track it down. So chances are you can use VIII-1, 2001 A03. Trick question: How do you know your vessel was built to Div. 1? Just use the allowable stress from the original edition of the code of construction. Hopefully you have a copy of the original code. If not, post the material and temperature and I can get you the allowable stress.
jt
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We are in the process of rerating most our pressure vessels as part of load up of our plant. I saw the following information from a consultant which may be of use to you.
"The ASME Boiler and Pressure Vessel Code Section VIII, Division 1, 1999 Addenda, and Code Case 2290 provide higher allowable stresses than those given in the previous editions of the code. This has permitted rerating of pressure vessels that could not be rerated before, or allowed pressure vessels that have thinned below the originally specified corrosion allowance to remain in service. However, the pressure vessel designers should be cognizant of certain restrictions prior to undertaking the task of performing the necessary calculations for rerating a pressure vessel, or determining the minimum required thickness of a pressure vessel for continued service."
"The ASME Boiler and Pressure Vessel Code Section VIII, Division 1, 1999 Addenda, and Code Case 2290 provide higher allowable stresses than those given in the previous editions of the code. This has permitted rerating of pressure vessels that could not be rerated before, or allowed pressure vessels that have thinned below the originally specified corrosion allowance to remain in service. However, the pressure vessel designers should be cognizant of certain restrictions prior to undertaking the task of performing the necessary calculations for rerating a pressure vessel, or determining the minimum required thickness of a pressure vessel for continued service."
jte and others;
I keep seeing people refer to the "original code of construction" mentioned in the NBIC as having to go back to the specific edition/addenda of the construction code that the object was built.
Let me clear this matter up - the phrase "original code of construction" does NOT refer to the specific edition/addenda of the construction code that the object was built. It refers to the code of construction document itself. This information is based on interpretation 95-19 in the NBIC. Thus, the original code of construction for a vessel built under ASME Section VIII, Div 1 is ASME Section VIII, Div 1, period.
I keep seeing people refer to the "original code of construction" mentioned in the NBIC as having to go back to the specific edition/addenda of the construction code that the object was built.
Let me clear this matter up - the phrase "original code of construction" does NOT refer to the specific edition/addenda of the construction code that the object was built. It refers to the code of construction document itself. This information is based on interpretation 95-19 in the NBIC. Thus, the original code of construction for a vessel built under ASME Section VIII, Div 1 is ASME Section VIII, Div 1, period.
metengr-
I fully agree with you. I didn't realize I was unclear on that in my post above when I said "...either the original edition or the latest edition. In fact, I believe there's an NBIC interpretation out there somewhere that says so..."
I guess the only thing I left out was that you could also choose an intermediate edition (though I'm not quite sure why anyone would do that...).
jt
I fully agree with you. I didn't realize I was unclear on that in my post above when I said "...either the original edition or the latest edition. In fact, I believe there's an NBIC interpretation out there somewhere that says so..."
I guess the only thing I left out was that you could also choose an intermediate edition (though I'm not quite sure why anyone would do that...).
jt
TangoCleveland
Mechanical
Using any ASME VIII-1 as original Code of construction was fine, until they released the 1999 edition. If you use the 1999 or more recent edition for a pre-1999 vessel, make sure you use allowables in pre-1999 Codes. The allowables changed in the newer Code to recognize advances in material/fabrication quality.
Larry
Larry
Actually both NBIC and API allow you to use the 1999 addenda stress values as long as the vessel was built in 1968 or later. There are a few other limitations, including lethal and cyclic service, but basically both allow you to calculate new tmins based on the new stress values if you wish to do so.
NBIC Interpretation 98-14 Question 5
API-579 A.2.3(b)(1)
Additionally, API-579 allows you to use Section VIII Div 2 stress values if the area of concern is located in a cylindrical, conical, or spherical shell, away from a weld or any other discontinuities.
API-579 A.2.3(d)
NBIC Interpretation 98-14 Question 5
API-579 A.2.3(b)(1)
Additionally, API-579 allows you to use Section VIII Div 2 stress values if the area of concern is located in a cylindrical, conical, or spherical shell, away from a weld or any other discontinuities.
API-579 A.2.3(d)
solinar (and metengr?)-
The API-579 Fitness For Service approach makes sense in my opinion as something you do to make it to the next opportunity you have to bring the vessel into Section VIII compliance. Thus, I believe it is inappropriate to take a FFS approach as a permanent solution.
The NBIC may allow rerates based on increased allowable stresses - but the jurisdictions may not. California is one jurisdiction which "will not entertain" requests to rerate pre-1999 vessels using the new allowables. I'm curious as to how the other jurisdictions are with this issue. Has anyone done a survey or have any direct knowledge?
jt
The API-579 Fitness For Service approach makes sense in my opinion as something you do to make it to the next opportunity you have to bring the vessel into Section VIII compliance. Thus, I believe it is inappropriate to take a FFS approach as a permanent solution.
The NBIC may allow rerates based on increased allowable stresses - but the jurisdictions may not. California is one jurisdiction which "will not entertain" requests to rerate pre-1999 vessels using the new allowables. I'm curious as to how the other jurisdictions are with this issue. Has anyone done a survey or have any direct knowledge?
jt
It is my understanding that the Commonwealth of Virginia does not allow re-rates with the higher ASME VIII allowable stresses.
Steve Braune
Tank Industry Consultants
Steve Braune
Tank Industry Consultants
When the NBIC was revised in 2001 to reflect the change in allowable stress values in the ASME B&PV code, this created a real hornets nest regarding repair/alteration activities especially for in-service, vessel re-ratings. As it turns out, the committee finally moved forward with permitting the use of higher allowable stresses to re-rate a pressure retaining item when it added RC-3024 , and RD-3010, paragraphs a)-f).
Keep in mind that the NBIC, like any other ANSI Standard, is intended to provide general technical guidance for Inspectors, Users and Jurisdictions. As with any Code, all scenarios cannot be accounted for, and this is where the Jurisdictions or Insurance Agencies have to step in and provided specific guidance. I have no problem using API 579 FFS to assure continued operation or even to support a re-rate. Component re-ratings need to be justified by adequate engineering calculation, that in my opinion (not the NBIC main committee) could include API 579 plus other technically sound approaches.
Since Jurisdictions are like small governing bodies, they can be all over the place on this very issue. If you would really like to know how many Jurisdictions have approved vessel re-rates, I would suggest contacting Mr. Robert Ferrell at the National Board. His number is 614-888-8320 X240.
Keep in mind that the NBIC, like any other ANSI Standard, is intended to provide general technical guidance for Inspectors, Users and Jurisdictions. As with any Code, all scenarios cannot be accounted for, and this is where the Jurisdictions or Insurance Agencies have to step in and provided specific guidance. I have no problem using API 579 FFS to assure continued operation or even to support a re-rate. Component re-ratings need to be justified by adequate engineering calculation, that in my opinion (not the NBIC main committee) could include API 579 plus other technically sound approaches.
Since Jurisdictions are like small governing bodies, they can be all over the place on this very issue. If you would really like to know how many Jurisdictions have approved vessel re-rates, I would suggest contacting Mr. Robert Ferrell at the National Board. His number is 614-888-8320 X240.
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