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
With one or more of the leak prevention,
detection, corrosion mitigation or containment
safeguards:
The initial internal inspection
date shall be based on
incremental credits for the
additional safeguards which
are cumulative.
API 653 Initial Inspection Interval
Tank Safeguard
Add to Initial Interval
Fiberglass-reinforced lining of the product-side of the tank
5 yrs
bottom installed per API 652.
Installation of an internal thin-film coating as installed per
2 yrs
API 652.
Cathodic protection of the soil-side of the tank bottom
5 yrs
installed, maintained and inspected per API 651.
Release prevention barrier installed per API 650, Annex I.
10 yrs
Bottom corrosion allowance greater than 0.150 in.
(Actual corrosion allowance 150 mils) / 15 mpy
API 653 Initial Inspection Interval
EXAMPLE
• With
•
•
Tank Safeguard of:
Thin-film coating
Release Prevention Barrier
API 653 Initial Inspection Interval
EXAMPLE
Initial Interval
Thin-film coating
Release Prevention Barrier
+10 years
+ 2 years
+10 years
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
If an RBI (Risk Based Inspection)
assessment has been performed,
the maximum initial internal
interval does not apply to tanks
storing the following:
EXCEPT…..
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.
API 653
Subsequent
Inspection
Interval
(re-inspection)
API 653 Subsequent Inspection Interval
Determined using the
corrosion rate procedures
6.4.2.3
Or, using the RBI
procedures
6.4.2.4
API 653 Subsequent Inspection Interval
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.
Hole 
API 653 Subsequent Inspection Interval
MRT = (Min of RTbc or RTip) – Or (StPr + UPr)
Steps for corrosion rate calculations
Determine reporting thickness
Coated Bottom
Uncoated Bottom
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
30 years
Interval of
API 653 Subsequent Inspection Interval
RBI
PROCEDURES
6.4.2.4
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.
Some people BEARly consider the
following….
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 conservativeprovided 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….