The IS 9964 Part 2 (1981) standard delivers detailed guidance on inspecting petroleum storage tanks to uphold their structural soundness and operational safety. It covers inspection intervals, various techniques such as ultrasonic thickness testing and vacuum leak detection, and assessment criteria for corrosion, settlement, and defects across different tank types including welded, riveted, floating roof, and cone roof tanks. This code is vital for sustaining the durability and safe functionality of petroleum storage tanks in refineries and storage sites.
Overview
The IS 9964 Part 2 (1981) standard delivers detailed guidance on inspecting petroleum storage tanks to uphold their structural soundness and operational safety. It covers inspection intervals, various techniques such as ultrasonic thickness testing and vacuum leak detection, and assessment criteria for corrosion, settlement, and defects across different tank types including welded, riveted, floating roof, and cone roof tanks. This code is vital for sustaining the durability and safe functionality of petroleum storage tanks in refineries and storage sites.
Audience
Contents
Structure
The scope of IS 9964 Part 2 (1981) encompasses planning and executing inspections and maintenance for atmospheric petroleum storage tanks. Key areas include internal and external examination methods (detailed in Appendices A, B, C), inspection documentation (Appendices D, F), pneumatic testing procedures (Appendix E), and roof structural measurements (Appendix G). Important appendices provide forms and tables for systematic inspection reporting, scheduling, and evaluation, such as external inspection reports, long-term and annual inspection plans, ultrasonic thickness data, and pneumatic test setups.
This section outlines mandatory adherence to legal frameworks including the Factories Act 1948 and Petroleum Act relevant to inspection, upkeep, and operation of storage tanks. Inspection scheduling uses long-term and yearly planning sheets (Appendices B & C), while comprehensive inspection reports cover structural elements such as roofs, shell plates, nozzles, vents, and valves with documented observations and repairs. Recommended inspection intervals and a workflow diagram guide compliance and maintenance activities.
Inspection aims to evaluate the internal and external conditions of tanks, detect corrosion, leaks, and structural defects, and facilitate maintenance planning to ensure safety and operational reliability. Essential documents for scheduling include long-term and yearly planning sheets (Appendices B & C) and detailed inspection and repair reports (Appendix D). The section presents typical inspection checklist items and emphasizes systematic documentation.
Inspection frequency is influenced by factors such as the nature of stored substances, visual maintenance findings, corrosion rates, construction details, and environmental conditions. Generally, external ultrasonic thickness measurements occur every five years, with internal inspections ranging from five to ten years depending on tank type and product corrosiveness. Inspection plans utilize scheduling sheets (Appendices B & C) supported by detailed reports (Appendix D).
Effective inspection management relies on using long-term and annual planning sheets (Appendices B & C) to schedule internal and external inspections. Inspection and repair reports (Appendix D) capture observations, repair works, and future inspection recommendations. Records must comply with legal requirements and be maintained by qualified personnel to ensure accountability and traceability.
Tank bottom inspection involves visual examination for pitting and rivet conditions, coupled with ultrasonic thickness measurements at specified locations including the center, periphery, and intermediate areas. Detailed recording of findings, including condition notes on foundations, nozzles, and supports, is essential. Planning sheets assist in scheduling systematic inspections and maintenance actions.
Leak testing comprises pneumatic tests using air pressure beneath the tank bottom with a sealing dam and water barrier, applying soap solution for leak visualization, and vacuum box testing post-repair to identify leaks before coating or hydrotesting. Tests must follow specified pressure levels and protocols to ensure early detection of leaks and prevent failures.
Inspection of tank shells includes ultrasonic thickness measurements externally (or internally if insulated), assessing welding efficiency, and comparing measured thicknesses against minimum allowable values. Pneumatic tests verify shell integrity. Inspection reports document all observations and repairs, enabling monitoring of shell condition and scheduling of maintenance.
This section covers ultrasonic thickness testing with specified welding efficiency factors, pneumatic leak testing, and focused inspections on rivet conditions for riveted tanks. Reporting formats and planning sheets ensure comprehensive documentation. Attention is given to detecting corrosion and structural deficiencies specific to tank fabrication type.
Roof inspections include visual checks from below or via scaffolding for cone roofs, measuring thickness and dimensions when corrosion or distortion is present, and adhering to acceptance limits including maximum allowable material loss. Repair criteria for roof plates and supporting members are described, with templates for recording measurements included.
Fittings such as roof drains undergo hydrostatic testing, while other components like nozzles, level indicators, and insulation are inspected for condition and defects. Ultrasonic thickness and pneumatic tests support evaluation. Inspection reports record conditions and repairs, ensuring fitting integrity and operational safety.
Guidance for evaluating tank foundation sag using a specified formula, limits on maximum tilting, and detection of uneven settlement is provided. Inspection includes identifying erosion, monitoring settlement rates, and implementing corrective measures like foundation repacking or tank lifting to maintain stability and safety.
Inspection focuses on verifying waterproof sealing annually and after rainy seasons to prevent moisture ingress that can cause hidden corrosion. Inspection reports document insulation condition and recommend remedial action. Planning sheets facilitate routine inspection scheduling and recordkeeping.
This appendix provides a template for scheduling internal inspections over several years, tracking inspection history, and planning future activities. It supports systematic long-term maintenance management.
A detailed example of monthly scheduling for internal inspections is presented, including tank identification, dimensions, stored product, and remarks. This supports adherence to inspection frequencies and comprehensive monitoring.
Frequently Asked
Inspection intervals depend on multiple aspects such as the characteristics of the stored substance including its corrosiveness and volatility, outcomes of visual maintenance checks, measured corrosion rates and allowances, results from prior inspections, construction and repair methods used, and environmental conditions like acidic atmospheres and risk zone locations. The standard recommends external ultrasonic thickness checks roughly every five years, while internal inspections vary from five to ten years depending on tank type and product.
The standard advocates visual inspections as the primary method to evaluate tank conditions and identify corrosion. On-stream inspections allow monitoring corrosion rates without tank shutdown. Non-destructive tests such as spot vacuum box tests for welds and dye penetration tests help detect leaks and surface defects. Internal inspections follow based on findings. This combination ensures early detection and effective maintenance planning.
Regular inspections should monitor settlement signs and unevenness. Limits include maximum unevenness of 10 mm per 10 m perimeter and 25 mm across the tank diameter. Minor settlement can be managed by cutting drainage channels and repairing sealing coats, while major settlement necessitates lifting the tank and reconstructing the foundation. Calculations for maximum allowable sag support assessment, and ongoing monitoring is essential to prevent structural issues.
Rivets must be rejected if their heads have worn down to about half their original thickness or diameter. Shell plates are evaluated based on measured thickness relative to minimum allowable values considering welding efficiency. Plates exhibiting buckling or severe corrosion, especially in the upper shell where thickness is minimal, require repair or replacement. Inspections must be done when tanks are fully filled with liquid to apply these criteria accurately.
Ultrasonic thickness measurements are carried out on tank shell plates across two adjacent plates on opposite sides. If thickness approaches minimum allowable limits, comprehensive evaluation of the entire course is performed. Plates below thresholds or showing localized thinning are candidates for renewal. Bottom plates receive multiple measurements at specified points based on pitting severity. Measurements are typically taken externally unless insulation necessitates internal access. Documenting exact measurement spots facilitates future comparisons.
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