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IS 9964:2000 (Part 2) is the Indian Standard (BIS) for recommendations for maintenance and operation of petroleum storage tanks, part 2: inspection. This standard provides guidelines for the inspection of above-ground, welded, atmospheric petroleum storage tanks. It covers inspection schedules, procedures for external and internal inspections, and requirements for record-keeping to ensure the integrity and safe operation of these assets.
Recommendations for Maintenance and Operation of Petroleum Storage Tanks, Part 2: Inspection
Overview
Status
Current
Usage level
Specialized
Domain
Materials Science — Structural Engineering and Structural Sections
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
Practical Notes
! This code is often used in conjunction with OISD-STD-129 (Inspection of Storage Tanks), which is a mandatory standard for many oil and gas operators in India.
! The inspection intervals mentioned are maximums; a Risk-Based Inspection (RBI) approach (as per API 580/581) is often adopted to define more optimized, condition-based intervals.
! Comprehensive documentation, including thickness monitoring locations (TMLs), corrosion rate calculations, and settlement records, is crucial for effective long-term asset integrity management.
API 2015:2021American Petroleum Institute (API), USA
HighCurrent
Requirements for Safe Entry and Cleaning of Petroleum Storage Tanks
Directly addresses procedures for preparing petroleum storage tanks for safe entry and work.
EI MCSP Part 16:2016Energy Institute (EI), UK
HighCurrent
Guidance on managing tank cleaning and inspection
Provides comprehensive guidance on the entire tank cleaning and inspection process, including safe entry.
NFPA 326:2020National Fire Protection Association (NFPA), USA
HighCurrent
Standard for the Safeguarding of Tanks and Containers for Entry, Cleaning, or Repair
Focuses on safeguarding tanks against fire and explosion hazards during entry, cleaning, and repair.
OSHA 29 CFR 1910.146Occupational Safety and Health Administration (OSHA), USA
MediumCurrent
Permit-required confined spaces
Provides the overarching legal framework and general requirements for any confined space entry in the US, including tanks.
Key Differences
≠IS 9964 specifies a very strict flammable vapor limit of <1% LEL for entry, whereas international norms like API 2015 generally permit entry up to <10% LEL (though 0% is the common operational target).
≠While IS 9964 is a 'recommendation' code, international standards like OSHA 29 CFR 1910.146 are legally enforceable regulations, and API 2015 is considered a mandatory industry requirement in many contexts.
≠API 2015 provides more specific quantitative 'action levels' for toxic substances like Benzene (0.5 ppm) that trigger mandatory use of supplied-air respirators, whereas IS 9964 broadly refers to 'permissible limits'.
≠International standards like EI 16 place a stronger, more explicit emphasis on a formal risk assessment and management of change (MOC) process for all tank entry and cleaning operations.
Key Similarities
≈All standards universally mandate a formal Permit-to-Work (PTW) or Confined Space Entry Permit system as a non-negotiable prerequisite for any tank entry.
≈Both IS 9964 and its international equivalents strongly recommend or mandate positive isolation (e.g., inserting blind flanges or spools) over simple valve isolation for all lines connected to the tank before entry.
≈The requirement for a designated standby person (attendant) to be present outside the tank at all times during entry is a fundamental safety principle shared across all standards.
≈All codes emphasize the critical need for continuous or periodic atmospheric testing and adequate ventilation (natural or mechanical) to maintain a safe atmosphere inside the tank during work.
Parameter Comparison
Parameter
IS Value
International
Source
Acceptable Oxygen Level for Entry
19.5% to 22.0%
19.5% to 23.5%
OSHA 29 CFR 1910.146
Flammable Vapors for General Entry
< 1% of LEL
< 10% of LEL
API 2015
Primary Isolation Method
Positive isolation by inserting blind flanges.
Positive isolation (blinding, spectacle blind, or removal of a spool piece).
API 2015
Hydrogen Sulfide (H2S) Limit
Within permissible limits (typically 10 ppm TWA in India)
< 10 ppm (OSHA PEL); many operators use a lower action level.
API 2015 / OSHA
Benzene Action Level
Within permissible limits (often ~1.6 ppm TWA in India)
0.5 ppm (Action Level requiring further controls).
API 2015
Hot Work Flammable Vapors Limit
Should be made completely gas-free (effectively 0% LEL).
0% LEL (continuous monitoring required).
API 2015
Standby Person Requirement
A trained person shall be stationed near the manhole.
At least one attendant is located outside the permit space for the duration of entry operations.
OSHA 29 CFR 1910.146
⚠ Verify details from original standards before use
Key Values5
Quick Reference Values
Minimum shell thickness for continued service2.5 mm
Maximum interval for internal inspection (default)10 years
Maximum interval for in-service external ultrasonic thickness survey5 years
Maximum interval for external visual inspection1 year
Frequency of routine (in-service) visual inspection1 month
Key Formulas
Corrosion Rate (CR) = (Original Thickness - Measured Thickness) / Time in years
Tables & Referenced Sections
Key Tables
Table 1 - Frequency of Inspection
Table 2 - Checklist for External Inspection of Tanks
Table 3 - Checklist for Internal Inspection of Tanks
How often should a petroleum tank be internally inspected?+
At least once every 10 years. This interval can be adjusted based on the calculated corrosion rate of the tank bottom and shell (Table 1 & Clause 6.1).
What is the minimum acceptable thickness for a tank shell?+
The tank should be considered for retirement if the shell plate thickness is less than 2.5 mm, although a fitness-for-service analysis may permit continued operation (Clause 6.2.2.1).
What does an external inspection involve?+
It includes checking the foundation for settlement, visual inspection of shell, nozzles, and roof for damage or corrosion, and ultrasonic thickness gauging at specified intervals (Clause 5).
Are API standards relevant when using IS 9964?+
Yes, IS 9964 frequently refers to API standards, especially API 653 (Tank Inspection, Repair, Alteration, and Reconstruction), for detailed procedures and acceptance criteria.