Changes in API 653, Tank Inspection, Repair, Alteration, and
By Stephen J. Gliebe, P.E.
The following highlights several changes to API 653 that are contained in
the Third Edition, Addendum 3, dated February 2008. Note that there is a
new, non-mandatory, Appendix H that provides guidance on performing a
similar service assessment. Highlights of the similar service assessment
methodology are also provided below.
Section 3: Definitions
New definitions have been added for candidate tank, control tank,
hydrotest, product-side, similar service assessment, and soil-side.
Section 4: Suitability For Service
- Roof: When a frangible roof-to-shell joint is required, a review
of items impacting compliance with API 650, Section 5.10.2, is
required (Para. 184.108.40.206).
- Vents: Vents shall be inspected for proper operation and screens
shall be verified to be free of obstruction (Para. 220.127.116.11.2).
- Bottom: Para. 4.4.3 has been renamed Tank Bottom Release
Prevention Systems. The sections covering cathodic protection and
internal linings have been expanded, and new sections covering
internal inspection and release prevention barriers were added.
Section 6: Inspection
Reporting requirements have been greatly expanded (Para. 6.9). Refer to
the sections covering report contents and recommendations for additional
Section 8: Reconstructed Tanks
All tanks that are reconstructed shall be checked for seismic stability
based on the rules of the current applicable standard (Para. 8.8).
Section 9: Tank Alteration and Repair
- Guidance is provided for installing a new bottom through an
existing tombstone reinforcing plate (Para. 9.9.4).
- Fixed roof repairs involving tank venting shall be made such that
normal and emergency venting meet the requirements of API Std. 650
- Fixed roof repairs involving modification to the roof structure
and the frangible joint shall be in compliance with the requirements
of API Std. 650 (Para. 18.104.22.168).
- Hot taps: Equations for calculating the hydrotest pressure of the
hot tap nozzle have been provided (Para. 22.214.171.124).
Section 11: Welding
A new section covering preheat or controlled deposition welding methods as
alternatives to post weld heat treatment has been added (Para. 11.3).
Section 12: Examination and Testing
Hydrotesting: A new section provides requirements for cases where a
hydrostatic test is not required, such as repairs or alterations to a
floating roof, and bottom repair or replacement outside the critical zone.
Appendix H: Similar Service Assessment
Appendix H, Similar Service Assessment, is new. The appendix provides a
detailed approach for establishing internal inspection intervals for tanks
for which corrosion rates have not been directly measured. Highlights of
the methodology and a partial data sheet are noted below. Refer to
Appendix H for complete details.
- Select a “control tank.” This is the tank for which service
conditions and corrosion rates are well known.
- Select the “candidate tank.” This is the tank to be compared to
the control tank to determine if similar service concepts apply.
- Complete the four assessments noted on the datasheets, including:
- Tank bottom product-side
- Tank bottom soil-side
- Shell product-side
- Shell external-side
- Determine the internal inspection interval
- Approve and file the completed data sheet
Partial Similar Service Assessment Data Sheet
(partial extract from API 653)