In-Service Tank Cleaning Inspection and Management.

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Gerald Gilbert
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1 In-Service Tank Cleaning Inspection and Management

2 Advanced Tank Solutions Desludging and Waste Management Comprehensive in-service inspection Tank shell and roof Annular plate Shell to floor welds Advanced robotic tank floor inspection Fully compliant to API 653 Tank Management and Maintenance Solutions

3 Storage Tank Types Crude Oil Floating roof Fixed roof with inner floater Up to 120 m in diameter Cone up Cone down Sloping Others Fuels (Diesel, Gasoline), Chemicals Water

4 Inspection of AST Floor Bottoms Using UT or MFL to Inspect AST Floor Bottoms represent two significantly different objectives. If the goal is to: 1.Repair the tank floor this requires removing the tank from service and conducting a floor scan with spot ultrasound prove up. 2.Extend the Schedule for the next out-of-service floor survey the use of an in service high density floor scan using ultrasound is a viable and cost effective method. In-service inspection offers benefits in situations where there is a low likelihood that repairs will be needed. * In-service inspections using high density UT scanning is designed to determine the most likely time that the tank should be removed from service for tank floor repair.

5 In-Service Inspections A full in-service floor inspection is provided Acoustic emission (AE) provides as near 100% coverage of the tank floor as geometry alllows In-service robotic inspection is performed with sampling coverage Density of coverage is guided by AE results as necessary Sampling coverage is defined to ensure reliable information on the floor minimum thickness Advanced statistical methods are used to assess the results

6 One Scenario of Usage Tank Age Integrity Result Recommendations 0 years QA/QC/Commissioning test pass Full API inspection using in-service S.O.N.A.R. robotics in 10 years 10 years In-service Robotic inspection RUL 20 + yrs Full API inspection using in-service S.O.N.A.R robotics in 10 years 20 years In-service Robotic inspection RUL 18 yrs Full API inspection using in-service S.O.N.A.R robotics or out of service in 10 years 30 years Inspection RUL 9 yrs Plan for Tank outage or use in-service S.O.N.A.R robotics for life extension years Take down tank and repair - planning time provided by feedback from in service robotics Use knowledge derived from previous in-service inspections to support procurement and repair planning.

The Cost of Cleaning and Inspecting an Aboveground Storage Tank Out-of-Service 1 Product Transfer 2 Out-of-Service Inspection 3 Cleaning and waste processing 4 VOC Emissions 7 22% 8 2% 9 2% 1 3% 2 5%

7 The Cost of Cleaning and Inspecting an Aboveground Storage Tank Out-of-Service 1 Product Transfer 2 Out-of-Service Inspection 3 Cleaning and waste processing 4 VOC Emissions 7 22% 8 2% 9 2% 1 3% 2 5% 3 15% 5 Environmental: Waste disposal 6 24% 5 15% 4 12% 6 Out-of-Service Lost Revenues 7 Alternative Tankage 8 Health and Safety Worker Protection Pollution Liability Insurance In-Service Oil Tank Cleaning and Inspection System: Results of Eight (8) Independent Validations, Silverman, E., Bass, R., Furillo, F and Wolf, A. ASNT Proceedings, Fall Conference, November 2000, pp

8 Robotics: Approximate Timescales Tank Diameter Inspection Only Cleaning 20 m 2 Days 3 Days 40 m 5 Days 6 Days 70 m 14 Days 16 Days Note Tank can remain in operation throughout the robotic operation

9 Product Filtration Configuration Clean Product Returned to Tank Add image of Mag Rover Clean Filtered Product Sludge/Sediment/Water Removed From Tank Wastewater/ Sediment First Phase Filter: 50 micron Separator/Coalescer Second Phase Filter: 5-25 micron

10 Manual Robot System consists of: 2 (4) UT immersion transducers Flushing system (optional) Pole assembly Manway seals (optional) Products < 205 C (400 F)

11 Potential Application Barriers Tanks with multiple internal obstructions on or near the floor. Tanks with internal floating roofs and fixed upper roof. Tanks with excessive sludge or with certain chemical content

12 Typical Robot Advanced S.O.N.A.R. 4 to 8 UT immersion transducers system. Suction and Discharge pumps (Optional) Umbilical cord and Carrier with 106M to 115M cable length. New Advanced S.O.N.A.R. Navigation system Video Sonar system data and screen shots recorded. Purge System for products below 37.5C Flashpoints. Camera and Light system (Optional do to products). Temperature range 20C to 50C

14 Ultrasonic Inspection: Bottom Side Corrosion Tank Floor Bottom-Side Corrosion

15 Ultrasonic Inspection: Bottom Side Corrosion

16 Ultrasonic Inspection: Top-Side Corrosion Tank Floor Tank Floor Top-Side Corrosion

17 Ultrasonic Inspection: Top-Side Corrosion

18 Tank Bottom Coverage Fixed Roof Legs Restricted Access Not possible to achieve 100% coverage of the tank floor

Calculating AST Remaining Useful Floor Life Scan accessible area Out-of-Service MFL Scanning In-Service UT Scanning (200,000 to >10 million UT readings) UT Prove-Up Distribution (usually 50-100 spot

19 Calculating AST Remaining Useful Floor Life Scan accessible area Out-of-Service MFL Scanning In-Service UT Scanning (200,000 to >10 million UT readings) UT Prove-Up Distribution (usually spot UT rdgs.) Detailed wall thickness and loss information for each scan Determine Deepest Pit or Thinnest Area Then Calculate Minimum Thickness and Remaining Useful Life RUL = (Design Thickness Measured Minimum Thickness) Use wall thickness distributions to make estimates for minimum Then Calculate Minimum Thickness and Remaining Useful Life Proportion of area Measured data Distribution fit Estimated minimum /Corrosion Rate Wall thickness (mm)

21 Example Driver for the In-service Approach Here the primary driver for the in-service approach was economic. The two 68m diameter tanks were being filled at a rate of circa BBLS of crude oil per day. Approximately every 6 days the product was sold off and the tanks emptied at a rate of some BBLS in 10 hrs. Inspecting the tank whilst in service allowed the client to continue their production and marketing without disruption. Additionally, from a CSR perspective an additional benefit was observed in the vast reduction in release of VOC s.

22 80 Meters Diameter Crude Oil Tank A continuing restriction to operations is the requirement to empty Storage Tanks (ASTs) for cleaning and inspection. The need to assure the mechanical integrity of ASTs can be critical as the environmental, social and economic consequences of failure, due to high probability damage mechanisms are ominous. GAP analysis concluded that: 1. Conventional inspection techniques are incapable of underwriting tank bottom floor integrity condition while the tank remains in service. 2. There is a finite limit to the inspection interval of Storage tanks. 3. Tank endorsement extension decisions are being supported by qualitative methods. 4. All cleaning/de-sludging activities are carried out only while the tank is out of service.

23 API Standard 653 API 653 references and objectives Paragraph Internal Inspection Intervals RBI applications Augment RBI-generated inspection intervals based on actual floor thickness measurements Federal and state perspective Depends on API 653 Edition State driven since clean water act SPCC guidelines API 653 guidance driven 1998 API653 committee voted in favour of including the alternative solution of using In-Service Robotic Thickness Measurements to comply with the requirement for a formal internal inspection. Shortly after this alternative was added to the 2nd edition as an addendum 2001 third edition modified to include this alternative 2014 fifth edition maintains the option to utilise In-Service Robotic Ultrasonic and the Probabilistic method to comply with the requirement for a formal internal inspection.

24 Excerpts from API Standard 653 Bottom Plate Thickness Bottom Plate Thickness Measurements A combination of these methods may be required along with extrapolation techniques and analysis to establish the probable conditions of the entire tank bottom Minimum Thickness for Tank Bottom Plate Other approaches such as the probabilistic method in may be used For the probabilistic method, a statistical analysis is made of thickness data from measurements (see 4.4.6) projecting remaining thickness, based on sample scanning of the bottom All tanks shall have a formal internal inspection conducted at the intervals defined by May be accomplished with the tank in-service utilizing various ultrasonic robotic thickness measurement and other on-stream inspection methods capable of assessing the thickness of the tank bottom, in combination with methods capable of assessing tank bottom integrity as described in If an in-service inspection is selected, the data and information collected shall be sufficient to evaluate the thickness, corrosion rate, and integrity of the tank bottom and establish the internal inspection interval, based on tank bottom thickness, corrosion rate, and integrity, utilizing the methods included in this standard.

25 Contact: Dornoch House, The Links, Birchwood, Warrington, WA3 7PB Tel: +44 (0)

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