AGENDA ITEM Title: Supported Roof Plate for Anchored Tank, F.7. Date: November 3, 2012

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1 AGENDA ITEM Title: Supported Roof Plate for Anchored Tank, F.7 Date: vember 3, 2012 Contact: Name: Tom Lorentz Company: AEC Engineering, Inc Phone: Purpose: Provide Design Rules for supported cone roof plate for Appendix-F, Anchored Tanks Source: B. Mistry dated 17 April 2010 Revision: 2 Impact: The business impact of this item is neutral. Rationale: Currently the design of roof and roof components per API-620 is invoked in chapter F7, but only for anchored Appendix-F tanks. Stresses in roof components are related to the type of roof and design pressure but are independent of the tank being anchored or not anchored. It is possible to transform an un-anchored tank into an anchored tank by addition of shell weight or adding concrete ballast (steel trough attached to shell and filled with concrete). Roof plates of supported cone roofs under internal pressure will lift up and will be subjected to hoop tension forces the same as self-supported roofs, regardless of anchorage. This agenda item proposes to invoke API-620 design equations when stresses in roof plates calculated per API-620, and (using joint efficiency of E=1.00) exceeds 7000 psi (101.5 Mpa). The roof components of Appendix-F tanks shall be designed using rules of API-620 and joint efficiency per API-620 and allowable stresses per API-650. The applicable equations and tables from API-620 shall be added to API-650, so as to make the standard as self-sufficient as possible. Ballot Format: New or amended items of text in the ballot are shown in red and underline; the deleted items are shown with a single line strikethrough. Text in italics is meant to be commentary, and shall not be included as part of the revision. Proposal: Revise and/or add as follows: Revise Figure F-1 Appendix F Decision Tree as shown Revision 2 of this item reverts to existing wording on section F.5.2 no change proposed. Change Numbering of Existing F.6 to F.7 Add New F.6 as follows: F.6 : Design of Roof Plates and Roof zzles ITEM Rev. 2 Page 1 of 4

2 F.6.1: Minimum thickness of supported and self-supporting cone roofs under internal pressure shall be calculated as follows: t := P R ( ) S d cos α + C a E R = nominal tank radius in m (in.) α = half apex angle of cone roof (degrees) cos(α) = cosine of half apex angle expressed as a decimal quantity S d = allowable stress for the design condition per this Standard in MPa, (lbf/in 2 ) C a = corrosion allowance in mm. (in.) as specified by the Purchaser (see 5.3.2) tes: 1. Thickness (t) of lap welded plates when controlled by internal pressure design shall 2. Calculated thickness (t) of roof plates shall not be less than that required under for supported cone or less than that required under for self-supporting cone roofs. F.6.2: Minimum thickness of self-supporting dome roofs under internal pressure shall be calculated as follows: 0.50 P R t := S d E + C a R = roof radius in m (in.) S d = allowable stress for the design condition per this Standard in MPa (lbf/in 2 ) C a = corrosion allowance in mm (in.) as specified by the Purchaser (see 5.3.2) tes: 1. Thickness (t) of lap welded plates when controlled by internal pressure design shall ITEM Rev. 2 Page 2 of 4

3 2. Calculated thickness (t) of roof plates shall not be less than that required under for self-supporting dome roofs. F.6.3: Minimum thickness of self-supporting umbrella roofs under internal pressure shall be calculated as follows: t := P R + C S d E a R = roof radius in m (in.) S d = allowable stress for the design condition per this Standard in MPa (lbf/in 2 ) C a = corrosion allowance in mm (in.) as specified by the Purchaser (see 5.3.2) tes: 3. Thickness (t) of lap welded plates when controlled by internal pressure design shall 4. Calculated thickness (t) of roof plates shall not be less than that required under for self-supporting umbrella roofs. Renumber existing F7.1 to F8.1 Content from existing F7.2 is relocated in revised F.5.2, and existing F7.2 is deleted F.7.2 The required compression area at the roof-to-shell junction of a supported cone roof shall be calculated as in F.5.1, and the participating compression area at the junction shall be determined by Figure F-2. For dome roofs and self-supporting cone roofs, the required area and the participating compression area shall be in accordance with of API Std 620, except the allowable compressive stress shall be increased to 140 MPa (20,000 lbf/in.2). te: When radial lap joints are included in the compression ring region, see API Std 620, Section , te 18, for an important design issue. Content from existing F7.3 has been revised and relocated in new F6, and existing F7.3 is renumbered and modified as follows. F.8.2: Roof plate, manway and nozzle materials shall conform to the specifications in this standard. Materials selected from API-650, Section 4 need not meet toughness criteria of F8.3: Roof manholes or nozzles conforming to Section are allowed to be used for internal pressures of up to six inches of water (1.5 kpa). Between six inches of water (1.5 kpa) and 1 psig (6.9 kpa) internal pressure, Section details are allowed if covers and flanges are ITEM Rev. 2 Page 3 of 4

4 increased to 3/8 inch (9 mm). For internal pressure above 1 psig (6.9 kpa) roof fittings shall use shell manhole and shell nozzle details. Alternatively, design of roof fittings per API Standard 620 is allowable. Equipment mating to these fittings shall have the equivalent drilling pattern and strength as the nozzle or manhole flange. F.7.3 The design and welding of roofs and the design, reinforcement, and welding of roof manholes and nozzles shall be completed with consideration of both API 650 and API 620. The design rules shall be as follows: 1. The thickness of self supporting roofs shall not be less than required by API 620, and , using API 650, Table 5-2, for allowable stresses and API 620, Table 5-2, for joint efficiency and radiography requirements. The thickness of self supporting roofs shall not be less than required by API 650, or , as applicable. 2. Roof plate, manway and nozzle materials shall be selected from API 650, Section 4. Materials need not meet toughness criteria of Roof manways and roof nozzles shall meet the requirements of API 650, through 5.7.6, for shell manways and nozzles. designed details for API 650 vary by height of liquid level, the values for the lowest liquid level may be used. Alternatively, roof manways and nozzles may be designed per API 620 using all the rules for API 620 roof manways and nozzles, including the 250 F maximum design temperature limitation. Change numbering of remaining paragraphs: F.7.4 through F.7.6 to F.8.4 through F.8.6 Search entire document for references to changed paragraph numbers update as needed. ITEM Rev. 2 Page 4 of 4

5 F-2 API STANDARD 650 Does tank have internal pressure? (1.1.1, 1.1.8, F.1.1, F.1.2, F.1.3 and F.7.1) Basic Design exceed weight of roof plates? (1.1.1) Basic Design exceed the weight of the shell, roof and attached framing? (F.1.2) Basic Design plus Appendix F.1 through F.6. Anchors for pressure not required. Do not exceed P max. Limit roof/shell compression area per F.5. Provide anchors and conform to F.7. exceed 18 kpa (2.5 PSIG)? (F.1.3 and F.7.1) API 650 with Appendix F or API 620 shall be used. Use API 620 Figure F-1 Appendix F Decision Tree