API 653 Tank Inspection Intervals Presented by: Mark A. Baker, P.E. Baker Consulting Group, Inc.
Inspection Frequency Considerations a) the nature of the product stored; b) the results of visual maintenance checks; c) corrosion allowances and corrosion rates; d) corrosion prevention systems; e) conditions at previous inspections; f) the methods and materials of construction and repair;
Inspection Frequency Considerations g) the location of tanks; h) the potential risk of air or water pollution; i) leak detection systems; j) change in operating mode k) jurisdictional requirements; l) changes in service
Internal inspection is required to: • Ensure that the bottom is not severely corroded and / or leaking. • Gather the data necessary for the minimum bottom and shell thickness assessments. • Identify and evaluate bottom settlement.
API 653 Initial Inspection Interval • The interval from initial service until the initial internal inspection shall not exceed 10 years.
API 653 Initial Inspection Interval • The initial internal inspection date shall be based on incremental credits for the additional safeguards which are cumulative. With one or more of the leak prevention, detection, corrosion mitigation or containment safeguards:
API 653 Initial Inspection Interval EXAMPLE • With Tank Safeguard of: • Thin-film coating • Release Prevention Barrier
API 653 Initial Inspection Interval • +10 years • + 2 years • +10 years EXAMPLE Initial Interval Thin-film coating Release Prevention Barrier Inspection Interval = 22 Years
API 653 Initial Inspection Interval The initial interval shall not exceed: • 20 years for tanks without a RPB • 30 years for tank with a RPB
API 653 Initial Inspection Interval EXCEPT….. If an RBI (Risk Based Inspection) assessment has been performed, the maximum initial internal interval does not apply to tanks storing the following:
API 653 Initial Inspection Interval 1. Viscous products which solidify at temperatures of 110°F or below.
API 653 Initial Inspection Interval 2 Any substance that is: not identified or regulated either as a hazardous chemical, and that the owner/operator has determined will not adversely impact surface or groundwater beyond the facility or affect human health or the environment.
(re-inspection) API 653 Subsequent InspectionInterval
API 653 Subsequent Inspection Interval 188.8.131.52 184.108.40.206 Determined using the corrosion rate procedures Or, using the RBI procedures
API 653 Subsequent Inspection Interval Hole During any examination to determine corrosion rates the owner/operator should ensure they understand the effectiveness of the inspection techniques employed for detecting and measuring potential damage mechanisms.
API 653 Subsequent Inspection Interval MRT = (Min of RTbc or RTip) – Or (StPr + UPr)
Steps for corrosion rate calculations Coated Bottom Uncoated Bottom Determine reporting thickness
Steps for corrosion rate calculations Scan the bottom Perform UT prove up to determine minimum thickness.
Finally - Calculate Subsequent Inspection MRT = (Min of RTbc or RTip) – Or (StPr + UPr)
API 653 Subsequent Inspection Interval Subsequent Inspection Interval with no RPB • Maximum Interval = 25 years
API 653 Subsequent Inspection Interval Subsequent Inspection Interval and a RPB • Maximum Interval of 30 years
API 653 Subsequent Inspection Interval RBI Procedures220.127.116.11
API 653 Subsequent Inspection Interval An owner/operator can establish the subsequent internal inspection interval using risk based inspection (RBI) procedures in accordance with API RP 580 and the additional requirements of API 653
API 653 Subsequent Inspection Interval The RBI assessment shall be performed by a team including inspection and engineering expertise knowledgeable in : • tank design, construction, and • modes of deterioration, and • the proper application of API RP 580 principles
API 653 Subsequent Inspection Interval The RBI assessment shall be reviewed and approved by a team at intervals not to exceed 10 years.
Factors to Consider in a RBI Assessment The tank design and material of construction Details about the foundation and surrounding area Operational history Inspection history Product characteristics Etc.
Consequences to Consider • Product type and volume • Mode of failure • slow leak, • bottom rupture, • Shell brittle fracture • Public health and safety • Environmental impact • Cost
RBI Inspection RBI Assessments may include other types of inspections such as acoustic emissions
RBI Assessments Perception is it provides a methodology to extend the inspection interval • May shorten the inspection interval • May result in additional focused inspections • Allows a company to focus its resources
Comparison Direct Measurements in API 653: Based on the sum of the product side and soil side bottom corrosion rates • Traditional approach for determining inspection intervals in API 653 • Tends to be a conservative approach because it is based on the sum of corrosion rates
Comparison RBI Assessment with 10-Year Update Assessments based on API 580/581 as implemented in API 653: Based on direct measurements or conservative-provided estimates of the bottom corrosion rates • Tends to be considered realistic estimates because it is based on the maximum corrosion rate of the bottom Then… If all else fails….