1. Comparison of EEMUA 159 to API Standards
Mark A. Baker, P.E.
National Petroleum Management Association’s
Petro May 28 – 31, 2012
Washington D.C.
Notes go here.

2. EEMUA 159
User’s Guide to the Inspection, Maintenance and Repair of Aboveground Vertical Cylindrical Steel Storage Tanks
Edition: 3rd Engineering Equipment and Materials Users Association / Jan-2003 / Amendments Feb-2004

3. API Standard 653
Tank Inspection, Repair, Alteration, and Reconstruction
Fourth Edition April 2009
Addendum 1, August 2010
Addendum 2, January 2012

4. API Standard 653 This document addresses:
Tanks built to API 650 and its predecessor API 12C.
Minimum requirements for maintaining the integrity
This standard employs the principles of API 650
Owner/operators may apply this standard to any tank constructed to a tank specification.
The standard covers steel storage tanks built to API Standard 650 and its predecessor API 12C. It provides minimum requirements for maintaining the integrity of such tanks after they have been placed in service and addresses inspection, repair, alteration, relocation, and reconstruction.
This standard employs the principles of API Std 650; however, storage tank owner/operators, based on consideration of specific construction and operating details, may apply this standard to any steel tank constructed in accordance with a tank specification.

5. EEMUA 159 This Standard addresses:
Establishment of essential inspection requirements for tanks.
Minimize problems and extend useful life.
Gives guidance on design features, common problems experienced during operation and on repair methods.
This addresses tanks built in accordance with British Standards
Where appropriate it refers to and makes use of international standards and codes such as those from API.
This publication is intended as a general inspection, maintenance and repair guide applicable tanks
Applies to the following codes:
British Standard, BS 2654
American Standard, API Std 650
German Code, DIN and 2
French Construction Code, ‘CODRES’
This Standard addresses:
The publican is intended primary to assist in the establishment of essential inspection requirements for aboveground, vertical, cylindrical, steel storage tanks, in order to minimize in-service problems and extend useful life. However for such requirements to be properly interpreted and understood, comprehensive guidance is given on many design features, on common problems experienced during operation and on repair methods.
This publican addresses, primarily, storage tanks built in accordance with relevant British Standards, but where appropriate it also refers to and makes use of commonly accepted international standards and codes such as those of the American Petroleum Institute. These differ little in the in-service conditions that they cover and the resulting inspection requirements. Accordingly, this publication is intended as a general inspection, maintenance and repair guide applicable to aboveground storage tanks

6. Inspector Qualifications
API 653
Authorized inspector
Must have experience and pass a written examination
Recertification is required every 6 years
Owner/Operator Inspectors
Must have knowledge tanks and local operating conditions
EEMUA 159
No certification process for tank inspectors
Inspectors should be experienced

7. Inspection Requirements
Routine External Inspections
API 653:
Required to be conducted on a Monthly Basis
EEMUA 159:
Required to be conducted on every 3 Months
The EEMUA requirements come from B.3
The document states that the inspection frequencies are for guidance only

8. Inspection Requirements
Formal External Inspections
API 653:
Required to be conducted the lesser of 5 years or the quarter corrosion rate life of the shell.
API 653
All tanks shall be given a visual external inspection by an authorized inspector. This inspection shall be called the external inspection and must be conducted at least every 5 years or RCA/4N years (where RCA is the difference between the measured shell thickness and the minimum required thickness in mils, and N is the shell corrosion rate in mils per year) whichever is less. Tanks may be in operation during this inspection.
EEMUA 159
See Table B.3 to see the actual recommended inspection frequency

9. Inspection Requirements
Formal External Inspections
EEMUA 159:
Ranges from 1 year to 15 year intervals. Factors include climate and type of product..
5 years – crude oil, and refined products with no internal liner
8 years finished products with internal liner
10 years for Jet A with internal liner
API 653
All tanks shall be given a visual external inspection by an authorized inspector. This inspection shall be called the external inspection and must be conducted at least every 5 years or RCA/4N years (where RCA is the difference between the measured shell thickness and the minimum required thickness in mils, and N is the shell corrosion rate in mils per year) whichever is less. Tanks may be in operation during this inspection.
EEMUA 159
See Table B.3 to see the actual recommended inspection frequency

10. Table B.3-1

11. Inspection Requirements
Formal Internal Inspections
API 653:
Based on the bottom corrosion rate not to exceed 20 years
Risk based inspection can be used – See API 580, “Risk-Based Inspection”.
MRT is:
0.100 for with no RPB or thick film liner
0.050 when RPB or Thick film liner is present
MRT = (Minimum of RTbc or RTip) – Or (StPr + UPr)
where:
MRT = minimum remaining thickness at the end of interval Or.
Or = in-service interval of operation (years to next internal inspection)
RTbc = minimum remaining thickness from bottom side corrosion after repairs,
RTip = minimum remaining thickness from internal corrosion after repairs,
StPr = maximum rate of corrosion not repaired on the top side.
UPr = maximum rate of corrosion on the bottom side.
API 653
EEMUA 159

12. Inspection Requirements
Formal Internal Inspections
EEMUA 159:
Based on Table B.3 Ranges from 3 years to 20 year intervals. Factors include climate and type of product.
8 years – crude oil
16 years finished products with internal liner
10 years finished products with no liner
Allows for use of probabilistic preventive maintenance – detailed explanation and guidelines are given.
MRT at next inspection 2.5 mm or 1.5 mm
EEMUA 159
MRT – 2.5 mm for tanks with foundation types A, B, or C (EEMUA 183 section 2)
MRT = 1.5 mm for tanks with foundations D or E or other foundations where leak detection and management systems have been installed (EEMUA 183)

13. Inspection Requirements
Formal Internal Inspections EEMUA 159:
EEMUA 159
This is Table B.3-1 Inspection Frequencies

14. Bottom Extension
API 653 requires a minimum thickness of inches at 3/8 inch from the shell- to-bottom weld.
EEMUA 159 requires a minimum of 2.5 mm (0.098 in) at 9.5 mm (0.374 in) from the shell-to-bottom weld
Approximately the same requirements for each document.

15. Inspection Requirements
Inspections Checklists Both API 653 and EEMUA 159 use the same checklists
EEMUA 159
MRT – 2.5 mm for tanks with foundation types A, B, or C (EEMUA 183 section 2)
MRT = 1.5 mm for tanks with foundations D or E or other foundations where leak detection and management systems have been installed (EEMUA 183)

16. Foundation Settlement
Differential Settlement
API 653 requires a total of D/10 survey locations with a minimum of 8. Tolerances are given as
Where:
S = maximum permissible deflection inft
L = arc length between measurements points in ft
YS = yield strength in lbf/in2
E = Young’s modulus in lbf/in2
H = tank height in ft
API 653 requirements from Appendix B. Alternative methods are currently being investigated by the committee

17. Foundation Settlement
Differential Settlement
EEMUA requires a total of D/10 survey locations with a minimum of 8 with the distance not exceeding 10 m.
Tolerances are given as:
100 mm (3.94 inches) between any two points at 10 m intervals
Alternatively
EEMUA 159

18. Foundation Settlement
Differential Settlement
Fixed roof tanks without an internal floating cover
EEMUA 159
The maximum differential settlement between any two point along the entire circumference measured near the bottom-to-shell connection should not exceed that shown in Figure
The maximum settlement should always be considered in combination with the allowable out-of-verticality of the tank shell and the tolerances of internal and external floating roof rim seals.

19. Foundation Settlement
Differential Settlement
Floating roof tanks and large fixed roof tanks equipped with internal floating covers of diameters exceeding 40 m
Where:
S = maximum permissible deflection in mm
L = arc length between measurements points in meters
YS = yield strength in MPa
E = Young’s modulus in MPa
H = tank height in meters
EEMUA 159
The extent of local differential settlement is determined from measurements plotted as shown on Figure (shown). From such a plot, the maximum out-of-plane deflection is determined by examining where the greatest deviation of the bottom from the optimum cosine curve occurs, over the shortest interval, between measurements. The above formula is used to calculate the maximum permissible out-of-plane deflection
This equation is the same as the equation in API Standard 653, Appendix B

20. Foundation Settlement
Planar Settlement
API 653 does not address planar tilt tolerance
EEMUA 159 permits a maximum out-of- verticality should not exceed h/100
API 653 does not address planar tilt tolerance although the standard does state the concerns with planar tilt (increased hoop stress, piping stress, ovality of the tank and seal clearance, etc) API 653 does have a requirement for plumbness of the tank shell to meet h/100 which is similar to the planar settlement requirement in EEMUA159
EEMUA 159 required out-of-verticality of h/100. When this limit is exceeded, releveling the tank and its foundation should be considered.

21. Settlement API 653 Edge Settlement API 653
Maximum allowable settlement Bew is shown in Figure B-10 for settled areas that include bottom lap welds essentially parallel to the shell (± 20 degrees). In settled areas where the measured settlement B exceeds 75 percent of allowed settlement Bew, all shell-to-bottom welds and bottom welds should be inspected visually and with magnetic particle examination or liquid penetrant examination. All indications should be repaired, or evaluated for risk of brittle fracture, and/or fatigue failure prior to returning the tank to service.
For settled areas where measured settlement B exceeds 75 percent of Bew, any welds within 12 in. of either side of the breakover area (see Figure B-5) should be examined visually. Any suspect areas should be examined with either magnetic particle examination or liquid penetrant examination. All indications should be repaired or evaluated for risk of fatigue prior to returning the tank to service.
Maximum allowable settlement Be is shown in Figure B-11 for areas of edge settlement with no welds, butt welds, or lap welds in the bottom that are essentially radial to the shell (± 20 degrees). In settled areas where the measured settlement exceeds 75 percent of the allowed settlement, all shell-to-bottom welds and bottom welds should be inspected visually and with magnetic particle examination or liquid penetrant examination. All indications should be repaired or evaluated for risk of brittle fracture and/or fatigue prior to returning the tank to service.
Maximum allowable settlement for areas of edge settlement with a lap weld at an arbitrary angle to the shell may be interpolated from Be and Bew from Figures B-10 and B-11, and the following formula:
B α = Be – (Be – Bew) x sin α
Where α is the angle of the weld to a tank centerline and B α is the allowable settlement for an area with a weld at that angle (see Figure B-12).

22. Settlement EEMUA 159 Edge Settlement
Maximum permissible edge settlement to 125 mm (4.92 in)over 750 mm (29.5 in)
If it is exceeded then the tank should be re- leveled
EEMUA 159 The maximum acceptable edge settlement is reached when A reaches a value of 125 mm over a width B of 750 mm. The tank should be re-leveled back to its original condition
Extra care should be taken when the edge deflection is over a short length of the periphery, as this may create high local stresses in the welds of the shell-to-bottom junction

23. Settlement API 653 Bottom Depressions
Maximum permissible bottom settlement or Bulges is given by:
BB = 0.37R
Where:
BB = maximum height of bulge or depth of local depression, in
R = radius of inscribed circle in bulged area or local depression, in ft

24. Settlement EEMUA 159 Bottom Depressions
Depressions are acceptable provided
The aspect ratio of height to width of the ripple is not greater than 75:500 (mm:mm) i.e – (3”:20”)
They do not form a severe crease over any of their length
In the event of ripples being unacceptable, they need to be cut out and the floor re-plated in the area of the ripples.
- Less conservative than API 653 the equivalent in 653 is aspect of height to width (diameter) is not greater than (in/in)

25. Settlement Center-to-Edge Settlement (Sagging)
API 653 – Does not directly address the overall center-to-edge settlement
EEMUA 159 – The maximum settlement is given as
When the difference in settlement between the center of the bottom and the periphery under the tank shell is excessive, the tensile stresses acting on the bottom starts to pull the shell-to-bottom connection inward and creates compressive stress that can lead to buckling.
API – This type of settlement is not specifically covered
EEMUA 159 – The equation displayed is based on the German standard DIN For a corroded tank bottom, a safety factor is recommended but not supplied in the publication

26. Shell Thickness
API 653
The evaluation of the existing tank shell shall be conducted by a storage tank engineer and shall include an analysis of the shell for the intended design conditions, based on existing shell plate thickness and material. The analysis shall take into consideration all anticipated loading conditions and combinations, including pressure due to fluid static head, internal and external pressure, wind loads, seismic loads, roof live loads, nozzle loads, settlement, and attachment loads.
The authorized inspector shall visually or otherwise decide which vertical plane(s) in the area is likely to be the most affected by corrosion. Profile measurements shall be taken along each vertical plane for a distance, L. In the plane(s), determine the lowest average thickness, t1, averaged over a length of L, using at least five equally spaced measurements over length L.
The criteria for continued operation is as follows:
The value t1 shall be greater than or equal to tmin (see or 4.3.4), subject to verification of all other loadings listed in ; and
The value t2 shall be greater than or equal to 60 percent of tmin; and
Any corrosion allowance required for service until the time of the next inspection shall be added to tmin and 60 percent of tmin.
Widely scattered pits may be ignored

27. Shell Thickness
EEMUA 159
The procedure for evaluation of tmin is essentially the same as API 653.
EEMUA adds a term for internal pressure which is not considered in API 653.
The procedure for determining tmin is essentially the same as provided in API 653 except that EEMUA 159 include a term to consider internal pressure

28. Shell Thickness
API 653 allows for the authorized inspector to determine the number and location of UT measurements during an inspection
EEMUA 159 requires a grid system for obtaining UT measurements
The chart shown is from Appendix A.1 for location of shell UTs

29. Roof Thickness API 653 EEMUA 159 Min of 0.090 in. in any 100 in2 area
Structure corrosion is to be evaluated
EEMUA 159
Min of 2 mm in a 500 mm by 500 mm area (0.079 in. in in2 area)
Structure corrosion is limited to 25% before replacement is required.

30. Brittle Fracture API 653 Assessment per Section 5 of API 653 EEMUA 159
No specific guidance for brittle fracture considerations

31. Repairs
API 653
Comprehensive repair section for the tank shell and bottom including nondestructive examination
Section 8 – Design Considerations for Reconstructed Tanks
Section 9 – Tank Repair and Alteration
Section 10 – Dismantling and Reconstruction
Section 12 – Examination and Testing
API 653
Has a comprehensive repair and reconstruction section
Details given for weld spacing
Details for nozzle installation and hot taps which is not considered in EEMUA

32. Repairs EEMUA 159 The document provides minimal guidance to the user.
The document refers the user to international standards
Appendix C has some examples for welding sequence and tank jacking
EEMUA 159
There is a significant section on tank jacking which is not included in API 653
There is a section on welding sequence for insert plates
The graphics show square lap welded patch plates – which is prohibited by API 653

33. Hydrostatic Testing API 653
Comprehensive section detailing when a hydrostatic test is required
Provides calculation for maximum fill level
Provides rules for foundation settlement surveys when settlement is anticipated.
API 653 has a comprehensive section regarding hydrostatic testing as far as detailing when a test is required and it requires foundation settlement measurements but does not detail when to take these measurements

34. Hydrostatic Testing EEMUA 159 Provides a detailed filling sequence
Water quality requirements
Provides a reprint from API 653 as well as discusses the BS 2654 requirements
Discusses survey requirements
EEMUA 159 copies much of API 653 into the hydrostatic testing section.
In addition there is a discussion of filling sequence and hold times to ensure that soils are not overloaded
Discusses the BS 2654 requirements in additional to API 653 requirements

35. Filling Sequence

36. EEMUA 159
Hydrostatic Test Flow Chart

37. Additional Requirements EEMUA 159
Details not in API 653:
Tank painting
Cathodic protection
Corrosion mechanisms
Product characteristics
Risk based inspection
Tank jacking
Detailed foundation design
Tank relocation
There are several topic which are included in EEMUA 159 which are not covered in detail in API 653 such as: (see list above)

38. Other information
Much of the information presented in EEMUA 159 is present in other API standards:
Tank painting - API 652
Cathodic protection - API 651
Corrosion mechanisms - API 570
Product characteristics - API 570
Risk based inspection - API 580
Tank jacking - API SCAST
studying this issue for inclusion in API 653
Foundation design - API 650 (Appendix B)
Tank relocation - API 653 (reconstruction)
Although many of the items are not covered in detail in API 653, the topics are covered in other API documents

39. Collaboration
No official collaboration between the two standards is underway
The Chairman of the EEMUA 159 committee has attended API SCAST meetings
Some members of the SCAST committee have attended EEMUA 159 meetings

40. Conclusions API 653 and EEMUA 159 are both good documents
API 653 provides a procedure to demonstrate that the tank inspector posses a minimum body of knowledge and experience
In general, API 653 is more conservative than EEMUA 159
EEMUA 159 contains information which fills in topics not covered in API 653
One of the primary factors to a good inspection is the knowledge and ability of the tank inspector. While I believe that a quality inspection can be obtained from either document, only API 653 requires the inspectors to meet a knowledge standard which is measured through examination which is not present in EEMUA I also feel that API 653 allows for flexibility in the evaluation of given condition beyond what is given in EEMUA API 653 also covers acceptable repairs to a greater extent than is present in EEMUA 159. While EEMUA 159 contains a great deal of information beyond what is present alone in API 653, the information can be found in other API documents such as API 575, API RP 2015, API RP 2016, etc.
Overall, I believe that API 653 is a comprehensive document and should be used as the standard for tank inspections. The use of EEMUA 159 as a companion document should be acceptable but when a conflict exists, I recommend that API 653 be the controlling standard.

41. Thank you Mark A. Baker, P.E. Baker Consulting Group, Inc.