Presentation on theme: "Comparison of EEMUA 159 to API Standards"— Presentation transcript:
1 Comparison of EEMUA 159 to API Standards Mark A. Baker, P.E.National Petroleum Management Association’sPetro May 28 – 31, 2012Washington D.C.Notes go here.
2 EEMUA 159User’s Guide to the Inspection, Maintenance and Repair of Aboveground Vertical Cylindrical Steel Storage TanksEdition: 3rd Engineering Equipment and Materials Users Association / Jan-2003 / Amendments Feb-2004
3 API Standard 653Tank Inspection, Repair, Alteration, and ReconstructionFourth Edition April 2009Addendum 1, August 2010Addendum 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 integrityThis standard employs the principles of API 650Owner/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 StandardsWhere 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 tanksApplies to the following codes:British Standard, BS 2654American Standard, API Std 650German Code, DIN and 2French 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 653Authorized inspectorMust have experience and pass a written examinationRecertification is required every 6 yearsOwner/Operator InspectorsMust have knowledge tanks and local operating conditionsEEMUA 159No certification process for tank inspectorsInspectors should be experienced
7 Inspection Requirements Routine External InspectionsAPI 653:Required to be conducted on a Monthly BasisEEMUA 159:Required to be conducted on every 3 MonthsThe EEMUA requirements come from B.3The document states that the inspection frequencies are for guidance only
8 Inspection Requirements Formal External InspectionsAPI 653:Required to be conducted the lesser of 5 years or the quarter corrosion rate life of the shell.API 653All 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 159See Table B.3 to see the actual recommended inspection frequency
9 Inspection Requirements Formal External InspectionsEEMUA 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 liner8 years finished products with internal liner10 years for Jet A with internal linerAPI 653All 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 159See Table B.3 to see the actual recommended inspection frequency
11 Inspection Requirements Formal Internal InspectionsAPI 653:Based on the bottom corrosion rate not to exceed 20 yearsRisk based inspection can be used – See API 580, “Risk-Based Inspection”.MRT is:0.100 for with no RPB or thick film liner0.050 when RPB or Thick film liner is presentMRT = (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 653EEMUA 159
12 Inspection Requirements Formal Internal InspectionsEEMUA 159:Based on Table B.3 Ranges from 3 years to 20 year intervals. Factors include climate and type of product.8 years – crude oil16 years finished products with internal liner10 years finished products with no linerAllows for use of probabilistic preventive maintenance – detailed explanation and guidelines are given.MRT at next inspection 2.5 mm or 1.5 mmEEMUA 159MRT – 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)
14 Bottom ExtensionAPI 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 weldApproximately the same requirements for each document.
15 Inspection Requirements Inspections Checklists Both API 653 and EEMUA 159 use the same checklistsEEMUA 159MRT – 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 SettlementAPI 653 requires a total of D/10 survey locations with a minimum of 8. Tolerances are given asWhere:S = maximum permissible deflection inftL = arc length between measurements points in ftYS = yield strength in lbf/in2E = Young’s modulus in lbf/in2H = tank height in ftAPI 653 requirements from Appendix B. Alternative methods are currently being investigated by the committee
17 Foundation Settlement Differential SettlementEEMUA 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 intervalsAlternativelyEEMUA 159
18 Foundation Settlement Differential SettlementFixed roof tanks without an internal floating coverEEMUA 159The maximum differential settlement between any two point along the entire circumference measured near the bottom-to-shell connection should not exceed that shown in FigureThe 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 SettlementFloating roof tanks and large fixed roof tanks equipped with internal floating covers of diameters exceeding 40 mWhere:S = maximum permissible deflection in mmL = arc length between measurements points in metersYS = yield strength in MPaE = Young’s modulus in MPaH = tank height in metersEEMUA 159The 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 deflectionThis equation is the same as the equation in API Standard 653, Appendix B
20 Foundation Settlement Planar SettlementAPI 653 does not address planar tilt toleranceEEMUA 159 permits a maximum out-of- verticality should not exceed h/100API 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 EEMUA159EEMUA 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 αWhere 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- leveledEEMUA 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 conditionExtra 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 = 0.37RWhere:BB = maximum height of bulge or depth of local depression, inR = radius of inscribed circle in bulged area or local depression, in ft
24 Settlement EEMUA 159 Bottom Depressions Depressions are acceptable providedThe 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 lengthIn 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 settlementEEMUA 159 – The maximum settlement is given asWhen 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 coveredEEMUA 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 ThicknessAPI 653The 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 ; andThe value t2 shall be greater than or equal to 60 percent of tmin; andAny 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 ThicknessEEMUA 159The 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 ThicknessAPI 653 allows for the authorized inspector to determine the number and location of UT measurements during an inspectionEEMUA 159 requires a grid system for obtaining UT measurementsThe 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 evaluatedEEMUA 159Min 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 RepairsAPI 653Comprehensive repair section for the tank shell and bottom including nondestructive examinationSection 8 – Design Considerations for Reconstructed TanksSection 9 – Tank Repair and AlterationSection 10 – Dismantling and ReconstructionSection 12 – Examination and TestingAPI 653Has a comprehensive repair and reconstruction sectionDetails given for weld spacingDetails 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 standardsAppendix C has some examples for welding sequence and tank jackingEEMUA 159There is a significant section on tank jacking which is not included in API 653There is a section on welding sequence for insert platesThe 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 requiredProvides calculation for maximum fill levelProvides 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 requirementsProvides a reprint from API 653 as well as discusses the BS 2654 requirementsDiscusses survey requirementsEEMUA 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 overloadedDiscusses the BS 2654 requirements in additional to API 653 requirements
37 Additional Requirements EEMUA 159 Details not in API 653:Tank paintingCathodic protectionCorrosion mechanismsProduct characteristicsRisk based inspectionTank jackingDetailed foundation designTank relocationThere 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 informationMuch of the information presented in EEMUA 159 is present in other API standards:Tank painting - API 652Cathodic protection - API 651Corrosion mechanisms - API 570Product characteristics - API 570Risk based inspection - API 580Tank jacking - API SCASTstudying this issue for inclusion in API 653Foundation 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 CollaborationNo official collaboration between the two standards is underwayThe Chairman of the EEMUA 159 committee has attended API SCAST meetingsSome 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 experienceIn general, API 653 is more conservative than EEMUA 159EEMUA 159 contains information which fills in topics not covered in API 653One 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.
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