OBSERVATION & TECHNICAL EVALUATION REPORT
API 653-BASED ASSESSMENT – SHELL DEFORMATION
1. EQUIPMENT / INSPECTION DETAILS
Tank Name
Component
UF Storage Tank
First Course of Tank Shell
Inspection Date
Inspection Type
Shell Nominal Thickness
Repair Type
8 mm
Internal welded lap patch
plate
10 mm
Tank Diameter
Patch Size
Localized
deformation/distortion
Accepted with Remarks
Likely Cause
Patch Thickness
Observed Condition
Report Status
Original Defect
Basis
03 September 2026
Visual Observation / API
653-Based Review
6.48 m
250 × 250 mm
Through-thickness hole in
shell
Welding heat input /
sequence
Photographs + API 653
repair requirements
2. PURPOSE
This report documents the observed condition of the first shell course following installation of an internal 250 × 250
mm × 10 mm thick welded patch plate over a through-thickness shell hole using SMAW process (WPS No. AWS
D1.1-WPS-G1G2-F4-011). The shell nominal thickness is 8 mm and the tank diameter is 6.48 m.
The assessment addresses localized shell deformation/distortion apparently produced by welding heat input during
installation of the patch plate and provides an API 653-based technical disposition.
3. PHOTO RECORD AND VISUAL OBSERVATIONS
Photo 1 – External view showing localized deformation around the welded repair.
UF Storage Tank – API 653 Observation Report | Shell Patch Plate Deformation | 04 September 2026
Photo 2 – Wider view showing the patch repair location, adjacent shell geometry and surrounding components.
Visible deformation area
Photo 3 – Sketch showing 7 patch plate including 5 Through-thickness hole in same shell course.
3.1 Observed Condition
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An internal welded patch plate measuring approximately 250 × 250 mm × 10 mm thick has been installed on
the first shell course to repair a through-thickness hole.
The surrounding 8 mm shell plate exhibits localized deformation/distortion adjacent to and around the patch
plate.
UF Storage Tank – API 653 Observation Report | Shell Patch Plate Deformation | 04 September 2026
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The deformation appears generally smooth and localized rather than an obviously sharp buckle or kink around
deformation the deformation area.
The repair area shows visible evidence of welding heat input around the perimeter.
No obvious open crack or shell tearing is visible observed.
The patch perimeter weld appears continuous in the visible portions, but weld soundness requires formal VT
and appropriate NDE which already been accepted.
4. API 653 TECHNICAL BASIS
API 653 permits shell repairs using lapped patch plates subject to specified design, material, fit-up, welding and
inspection requirements. API 653 also requires fit-up, heat input and welding sequence to be considered to reduce
distortion when welding repair/replacement plates to an existing tank shell. The observed deformation therefore
requires individual evaluation rather than acceptance solely from visual site inspection.
For lapped shell patch repairs, applicable requirements include minimum patch dimensions, appropriate patch
thickness/design, forming the patch to the shell radius, and restrictions concerning distorted areas. The final repair
must therefore be verified against the approved repair drawing/procedure.
5. PATCH PLATE DIMENSIONAL REVIEW
Parameter
Patch dimension
Provided
250 × 250 mm
Patch thickness
10 mm
Shell thickness
8 mm
Patch forming
Internal patch; shell
distortion observed
Welded around patch
Perimeter weld
API 653 Basis
Minimum lap-patch
dimension is 100 mm
Patch thickness shall not
exceed the shell thickness
by more than one-third
Remaining thickness must
satisfy applicable
requirements
Patch to be formed to shell
radius
Continuous/full-fillet
perimeter weld as applicable
Assessment
Meets minimum dimension
Within stated limit;
Verified by the previous
inspection report which still
be accepted.
Manually formed and fitted.
VT + MT/PT required
(accepted)
6. DEFORMATION / DISTORTION EVALUATION
The observed distortion is considered localized welding-induced shell deformation associated with installation of the
internal patch plate. API 653 requires welding practices to consider fit-up, heat input and welding sequence to
minimize distortion.
Acceptance is therefore subject to verification that the deformation is smooth, stable and does not compromise the
shell or patch repair.
7. REQUIRED VERIFICATION / INSPECTION
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Measure and record the maximum deformation/bulge depth using a suitable dimensional method.
Confirm that the deformation is smooth and gradual and does not contain a sharp buckle, kink or crease.
Perform detailed visual examination (VT) of the shell and patch perimeter weld.
Perform MT or PT of the patch perimeter weld and affected shell area as applicable.
Perform UT thickness measurements around and adjacent to the deformed area to verify remaining shell
thickness.
Verify absence of cracks, tears, laminations, arc strikes and other unacceptable discontinuities.
Verify perimeter weld size, continuity and workmanship against the approved WPS and repair detail.
Confirm the patch plate design and attachment are adequate for service and hydrostatic loads.
UF Storage Tank – API 653 Observation Report | Shell Patch Plate Deformation | 04 September 2026
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Record the final deformation measurement as a baseline for future inspection.
8. CONCLUSION AND ACCEPTANCE
ACCEPTED WITH REMARKS – SUBJECT TO API 653 INDIVIDUAL EVALUATION
Based on the visual inspection, the installed 250 × 250 × 10 mm internal patch plate has resulted in localized shell
distortion at the first shell course. The visible deformation appears generally smooth and gradual, and no obvious
crack or shell tearing is visible. However, MPI is highly recommended to the affected distorted area.
The condition can potentially be accepted following an API 653 individual evaluation if the following conditions are
verified and documented:
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the deformation is a smooth, gradual bulge, rather than a sharp buckle or kink;
no cracks are present;
no shell tearing or lamination is found;
patch-plate perimeter weld is sound;
VT/MT/PT/UT results are satisfactory;
shell remaining thickness is adequate;
patch plate is properly designed and attached; and
the deformation is stable with no evidence of progressive distortion.
If all of the above conditions are satisfactorily demonstrated and accepted by the API 653 Qualified
Inspector/Owner's Inspector, the observed deformation may remain in service without immediate removal solely
because of the visible distortion. Final acceptance should be recorded with the measured deformation profile and
supporting NDE/UT results.
9. REMARKS / RECOMMENDATIONS
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Do not perform additional heating, straightening or mechanical impact on the deformed shell unless specifically
engineered and approved.
Record the maximum deformation measurement and retain it as a baseline for future API 653 inspections.
If the deformation is sharp, kinked, cracked, unstable, or increasing, suspend acceptance and refer the
condition for engineering evaluation and repair disposition.
Any further repair shall use an approved repair procedure, qualified WPS/PQR and qualified welders.
Maintain this repair/deformation record in the tank inspection history.
UF Storage Tank – API 653 Observation Report | Shell Patch Plate Deformation | 04 September 2026