The Above Ground Storage Tank Inspection provides you with information about the inspection of storage tanks and storage tank testing in a construction shop and site, as well as storage tank in-service inspection in operating units. You may review storage tank inspection procedure and storage tank ITP articles.
What is the Application of a Storage Tank?
There are two kinds of storage tanks, the Atmospheric Storage Tank and the Low Pressure Storage tank.
The maximum pressure for vapor or gas space of an atmospheric storage tank is 2.5 psi, and for a low pressure storage tank is 15 psi.
If the pressure is more than 15 psi, the liquid cannot be stored in in the storage tank and it is necessary to be stored in a pressure vessel.
Atmospheric storage tanks are used for storing crude oil, heavy oil, gas oils, furnace oils, naphtha, gasoline, non-volatile chemicals, etc.
Low pressure storage tank are used for storing light crude oil, some gasoline blending stock, light naphtha, pentane, some volatile chemicals, liquid oxygen, liquid nitrogen, etc.
The physical shape of both kinds of above stated storage tanks might be similar, but the construction code and design and inspection requirements are different.
What are the Above Ground Storage Tank Inspection Requirements in the Manufacturer Shop and at the field?
The construction code for the atmospheric storage tank is API STD 650, and for a low pressure storage tank is API STD 620. These cover the minimum requirements for design, materials, fabrication, inspection and testing.
With the above explanation, your inspection and test plan (ITP) for storage tank construction needs to meet the requirements of either API STD 650 or API 620.
The storage tank inspection and test plan summarize all inspection requirements in several pages and in tabular format.
The storage tank inspection and test plan is prepared in two sections, one for the supply, cutting, rolling and beveling of storage tank plates in the manufacturer’s shop, and the other section for construction activities in the field.
The prepared plates in the shop are transferred to the field for assembly. Depending on the client’s contract, sometimes there is only one contractor for shop and field activities, and sometimes there are two contractors one for the shop and one for field assembly.
This table determines each party’s responsibility (i.e. construction contractor, third party inspector and client).
For more detailed information on above ground storage tank inspection both on in-shop and on-site review the following articles:
Third Party Inspection for Storage Tank
Inspection and Test Plan for Storage Tank
What are the Above Ground Storage Tank Inspection Requirements in Operating Plants?
The In-Service Inspection code for your atmospheric storage tank is API STD 653. The content in this standard covers tank inspection, repair, alteration and reconstruction.
It is necessary for you to use this standard with the API Recommended Practice 575, which is titled “Guidelines and Methods for Inspection of Existing Atmospheric and Low-pressure Storage Tanks.”
As you see above, the API STD 653 addresses only the atmospheric storage tank, but API RP 575 covers both atmospheric and low pressure storage tanks.
The API STD 653 is designated for atmospheric above ground storage tank inspection, for tank built based on API 650, but you may use this code for any steel tank with specific consideration and operating details.
Some other recommendation practices that you need to take into account in your above ground storage tank inspection are API RP 651 for tank bottom plates cathodic protection system, API RP 652 for tank internal lining system, API RP 571 for damage mechanism, and API 577 for welding inspection and metallurgy. Many of the design, welding, examination, and material requirements of API 650 can be applied in the maintenance inspection, rating, repair, and alteration of in-service tanks.
But if you found a conflict between the construction code API 650 and API 653, the requirement of API 653 must govern this standard, as it -specifically addresses above ground storage tank inspections for operating plants.
API 653 above ground storage tank inspectors are qualified for the inspection of storage tanks, as they are certified by API for such activities.
What are Important Points in the Above Ground Storage Tank Inspection in shutdown?
For detailed information you need to refer to API STD 653 and API RP 575.
Internal Inspection-Shell Plate
- Shell plate inspection for corrosion and deformation
- Shell plate circumferential and longitudinal welding joints inspection for corrosion and cracking
- Internal coating inspection (if any)
Internal Inspection- Bottom Plate
- Thickness measurement and remaining life calculation on bottom plates and annular plates
- Bottom plates and annular plates inspection for corrosion and deformation
- Bottom plates and annular plates welding joints inspection for corrosion and cracking specifically the annular plate joints with first shell course plate
- Sump inspection
- Internal coating inspection (if any)
- Inspection of sample plate, which must be cut to find any external corrosion
- Vacuum testing inspection and supervision
Internal Inspection-Fix Roof
- Roof plate inspection for corrosion and deformation
- Roof structure members inspection for corrosion and deformation
- Roof plates and structure members welding joints inspection for corrosion and cracking
- Internal coating inspection (if any)
Internal Inspection-Floating Roof
- Roof plate inspection for corrosion and deformation
- Roof structure members inspection for corrosion and deformation
- Roof plates and structure members welding joints inspection for corrosion and cracking
- Roof sealing system inspection i.e. rubber seal, seal plate, etc.
- Roof leg supports inspection
- Pontoon gasoil leak testing
- Internal coating inspection (if any)
- Roof drain system inspection
Internal Inspection-Internal Equipment
- Gage pole inspection for corrosion and deformation
- Support and structure members inspection for corrosion and deformation
- Inspection of columns for corrosion and deformation
- Fixed coil inspection and test for corrosion
External Inspection-Shell and Roof
- Thickness measurement and remaining life calculation
- Shell and roof plates inspection for corrosion and deformation
- Shell and roof plates circumferential and longitudinal welding joints inspection for corrosion and cracking
- Nozzles, man ways, flange welding joints inspection for corrosion and cracking
- External part of annular plates inspection, specifically welding joint with shell plates
- Side vents inspection
- Gasket seating surface inspection of nozzles and man ways flange joints
- Top angle, wind girder and stair way inspection for corrosion and deformation
- Roof sump inspection (floating roof only)
- Pontoon and pontoon structure welding joints inspection for corrosion and cracking (floating roof only)
- Weather shield rubber and pontoon doors rubber inspection (floating roof only)
- Pontoon air leak testing (internal floating roof only)
- Painting or insulation inspection
External Inspection-Foundation
- Concrete foundation inspection for corrosion and cracking
- Earthling system inspection
- Asphalt inspection (around shell)
- Cathodic protection system inspection
Executive Summary & Industrial Inspection Scope
In demanding industrial environments across Oil, Gas, Petrochemical, Offshore, and Heavy Process Infrastructure, rigorous compliance with ISO 9001 / ASME / API is essential to ensure operational integrity, personnel safety, and compliance with statutory regulatory frameworks. This technical specification provides QA/QC managers, procurement engineers, welding inspectors, and third-party inspection (TPI) agencies with an authoritative, field-tested guideline for “Above Ground Storage Tank Inspection”.
Ensuring compliance regarding above ground storage tank inspection minimizes the risk of catastrophic asset failures, costly unscheduled shutdowns, and supplier non-conformances. The following technical sections delineate the scope of inspection, mandatory verification protocols, acceptance criteria, documentation deliverables, and root cause mitigation strategies.
Governing International Engineering Codes & Specifications
Verification and validation of Above Ground Storage Tank Inspection must strictly conform to the latest editions of the following international engineering codes and project specifications:
• **Primary Standard Reference:** ISO 9001 / ASME / API
• **Quality Management & Inspection Systems:** ISO 9001:2015 & ISO/IEC 17020 (Requirements for the operation of various types of bodies performing inspection)
• **Material Compliance & Traceability:** EN 10204 Type 3.1 / 3.2 Inspection Certificates for metallic and non-metallic pressure-retaining components
• **Personnel Qualification:** ASNT SNT-TC-1A / ISO 9712 for NDT personnel, CSWIP 3.1 / AWS CWI for welding inspection, and NACE / AMPP Level 2/3 for coating and corrosion personnel
• **Statutory & Health Safety Directives:** ASME Boiler & Pressure Vessel Code (BPVC), API Standards, OSHA, and regional local authority regulations.
Step-by-Step Quality Control & Inspection Procedure
The execution of quality surveillance for Above Ground Storage Tank Inspection is structured across four progressive QA/QC intervention phases:
Stage 1: Pre-Inspection & Engineering Document Review (Review Point – R)
Prior to commencement of any physical activities or manufacturing operations related to Above Ground Storage Tank Inspection, the contractor or vendor must submit all technical submittals to the Owner or TPI agency for formal review and approval.
- Verification of approved Inspection and Test Plan (ITP) identifying all Hold (H), Witness (W), Review (R), and Surveillance (S) intervention points.
- Cross-examination of Material Test Reports (MTR / Mill Certificates) against standard design specifications (ISO 9001 / ASME / API).
- Review and approval of specific Procedure Qualification Records (PQR), Welding Procedure Specifications (WPS), or calibration certificates.
- Verification that all measurement instruments, gauges, and NDT equipment hold valid calibration certificates from ISO/IEC 17025 accredited calibration laboratories (within 6 to 12 months validity).
Stage 2: In-Process Witnessing & Fabrication Control (Witness / Hold Point – W/H)
During the active execution phase, the certified inspector performs physical surveillance to ensure strict adherence to certified drawings, manufacturing procedures, and code tolerances.
- Verification of material traceability (heat number, heat treatment lot, plate number) transferred accurately onto fabricated components.
- Dimensional verification and visual inspection using calibrated gauges, micrometer depth dials, or laser alignment systems.
- Monitoring ambient environmental parameters (relative humidity, dew point, substrate temperature) when applying surface treatments, welding preheat, or pressure testing.
- Witnessing non-destructive examination (RT, UT, MT, PT, PMI) at specified percentages according to project critical rating and code requirements.
Stage 3: Final Acceptance, Pressure/Performance Testing & Marking (Hold Point – H)
The culminating milestone where the fully assembled or completed item is subjected to definitive acceptance tests in the presence of the Owner’s Third-Party Inspector (TPI).
- Execution of pressure proof tests (Hydrostatic at 1.3x to 1.5x MAWP or Pneumatic test) with dual calibrated pressure gauges and temperature recorders.
- Full visual inspection of completed surfaces, welds, protective coatings, and flange contact faces for absence of mechanical damage or code defects.
- Validation of permanent stamping, low-stress die markings, nameplate data verification, and barcoding in strict conformity with project specs.
- Clearing all open punch-list items, non-conformance reports (NCRs), and concession requests prior to issuance of the release note.
Stage 4: Packing, Preservation & Inspection Release (Inspection Release Certificate – IRC)
Ensuring the inspected equipment is adequately protected against atmospheric corrosion, mechanical shock, and marine transit degradation.
- Inspection of rust preventative coatings, desiccant bags, flange face blind protectors, and vapor corrosion inhibitor (VCI) packaging.
- Verification of heavy-lift sea fastening lugs, center-of-gravity markings, and export crating compliance (ISPM 15 wooden crating).
- Compilation and signing of the final Inspection Release Certificate (IRC / Shipping Release) and manufacturer data dossier (MDR).
Technical Acceptance Criteria & Tolerances Matrix
All measurements and physical characteristics must comply with the engineering tolerances and acceptance thresholds tabulated below:
| Inspection Parameter / Test Item | Applicable Standard & Clause | Permissible Tolerance / Acceptance Limit | Verification Method | Intervention Type |
|---|---|---|---|---|
| Material Chemical & Mechanical Verification | ISO 9001 / ASME / API / EN 10204 3.1 | 100% compliance with minimum tensile, yield, elongation, and impact values (Charpy V-Notch at design temp) | Optical Emission Spectrometry (OES) / MTR Verification | Review (R) |
| Visual & Dimensional Tolerances | ISO 9001 / ASME / API / Project Specs | Zero cracks, lack of fusion, severe pitting; dimensional tolerances within ±1.0mm to ±3.0mm per code drawings | Calibrated Vernier, Bridge Cam, Depth Micrometer | Witness (W) |
| Non-Destructive Examination (NDT) | ASME Sec V / ASNT SNT-TC-1A | 100% compliant with code acceptance criteria; zero planar defects or unpermitted volumetric indications | Radiographic (RT) / Ultrasonic (UT) / Magnetic Particle (MT) | Hold (H) |
| Pressure / Proof Testing (Hydrostatic) | ISO 9001 / ASME / API / ASME Sec VIII | Test pressure maintained for minimum 30 to 60 mins; zero pressure drop, zero leakage or visible sweating | Dual calibrated Bourdon pressure gauges + Chart Recorder | Hold (H) |
| Surface Prep & Protective Coating Quality | SSPC-SP / NACE / ISO 8501 | Surface profile 50 – 75 µm; Dry Film Thickness (DFT) within 80/20 rule of specified nominal thickness | Replica Tape (ASTM D4417) & Magnetic Gauge (SSPC-PA 2) | Witness (W) |
| Nameplate & Final Preservation Verification | API / ASME / Client Specs | 316L SS nameplate securely affixed with correct design code, MAWP, design temp, and national board stamping | Physical visual check & VCI preservation verification | Hold (H) |
Mandatory QA/QC Dossier & Inspection Deliverables
Prior to the final issuance of the Inspection Release Certificate (IRC), the contractor and vendor must compile and submit the verified manufacturer data record containing:
- Approved Inspection & Test Plan (ITP) with sign-off stamps by Contractor, Client, and TPI.
- Material Test Reports (MTR / Mill Test Certificates EN 10204 Type 3.1 or 3.2).
- Certified Welding Procedure Specifications (WPS), Procedure Qualification Records (PQR), and Welder Performance Qualifications (WPQ).
- Calibration Certificates for all test instruments and measuring equipment (NABL / ISO 17025 accredited).
- Non-Destructive Examination Reports (RT, UT, MT, PT, PMI, Ferrite Content) evaluated by Level II/III inspectors.
- Heat Treatment & PWHT Time-Temperature Recorder Charts with thermocouple layout drawings.
- Hydrostatic / Pneumatic Pressure Proof Test Certificate with calibrated chart recorder logs.
- Surface Preparation and Protective Coating Inspection Reports (Daily environmental log, blast profile, DFT summary).
- Non-Conformance Report (NCR) and Concession Disposition Closeout Log.
- Official Inspection Release Certificate (IRC / Shipping Release Note) permitting packing and dispatch.
Common Non-Conformances & Field Mitigation Strategies
Based on extensive third-party inspection field records in oil & gas projects, the following deviations require heightened surveillance:
Defect / Hazard: Material Grade Substitution & Lack of Heat Traceability
Root Cause: Uncontrolled workshop storage, missing color coding, or unverified supplier sub-tier procurement without EN 10204 3.1 documentation.
Preventative Action: Enforce strict 100% Positive Material Identification (PMI) prior to cutting, and mandatory material receiving inspection with physical stamping cross-referenced to original mill test certificates.
Defect / Hazard: Out-of-Tolerance Fit-Up & Alignment Mismatch
Root Cause: Poor thermal cutting, thermal distortion from excessive preheat, or inadequate jigging and tacking arrangements.
Preventative Action: Establish a mandatory Witness/Hold point at joint fit-up before root pass deposition. Use calibrated Hi-Lo gauges to verify bevel angle, root face, and root gap according to the qualified WPS.
Defect / Hazard: Premature Coating Delamination & Blistering Under Film
Root Cause: Excessive soluble salt contamination (>20 mg/m²) left on the substrate, blast cleaning below dew point (<3°C above dew point), or oil/moisture in the blasting compressor air line.
Preventative Action: Perform Blotter Test (ASTM D4285) daily on compressed air, enforce Bresle patch chloride testing, and apply primer within 4 hours of abrasive blasting before rust blooming initiates.
Defect / Hazard: Pressure Drop During Final Hydrostatic Proof Testing
Root Cause: Micro-leakage through temporary test flange gaskets, entrapped air pockets inside vessel high points, or inadequate temperature stabilization.
Preventative Action: Ensure thorough venting at all high-point vents until bubble-free fluid emerges, allow minimum 15-minute temperature stabilization between filling medium and ambient metal, and torque all blind flanges with calibrated torque wrenches.
Frequently Asked Questions (FAQ)
Q: What are the mandatory qualifications for inspectors verifying Above Ground Storage Tank Inspection?
A: Inspectors must hold recognized international certifications applicable to the discipline. For welding and fabrication: CSWIP 3.1/3.2, AWS CWI, or API 510/570 Source Inspector. For NDT: ISO 9712 or ASNT SNT-TC-1A Level II minimum. For coatings: NACE / AMPP Level 2 or FROSIO Level III. Additionally, the inspection agency must operate under an ISO/IEC 17020 accredited quality management system.
Q: How does PtroTek resolve non-conformances (NCRs) encountered during vendor surveillance?
A: When a deviation from certified drawings or ISO 9001 / ASME / API is detected, the inspector issues a formal Non-Conformance Report (NCR) within 24 hours. The vendor must submit a Root Cause Analysis (RCA) and proposed disposition (Rework, Repair, or Concession). Work on the affected component is halted (Hold Point) until the Owner’s engineering authority approves the disposition and a re-inspection confirms full compliance.
Q: What is the difference between Witness (W) and Hold (H) points in an Inspection & Test Plan (ITP)?
A: A Hold Point (H) is a mandatory milestone where fabrication or testing CANNOT proceed without the physical presence of the designated client or third-party inspector. Written clearance or stamping is strictly required. A Witness Point (W) requires prior notification (typically 24 to 48 hours) to the inspector; however, if the inspector fails to attend at the scheduled time, fabrication or testing may proceed with subsequent review of the test records.
Q: Can international clients review inspection reports and photos in real time?
A: Yes. PtroTek provides comprehensive Flash Reports issued within 24 hours of inspection completion, followed by detailed formal inspection reports accompanied by high-resolution calibrated photographic evidence, dimension logs, and signed vendor test records for complete global transparency.
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