QUESTION / RESPONSE
May only the materials listed in API 620 Section 4 and Appendices Q, R, and S be used in API 650 F.7.3 roofs?
If materials other than those listed in API 620 are to be permitted, how are the design allowables to be established?
Are the maximum allowable stresses to be used in roof design those of API 620?
Must the joint efficiencies of API 620 Table 5-2 be applied to the roof?
May the radiography examinations of API 620 Section 5.26.4 be used for applicable roof butt joints to achieve a higher joint efficiency?
If the maximum design temperature is not limited to 250 degrees Fahrenheit and less as suggested by the response to the second question of Inquiry 650-I-39/00, how is one to modify the material properties in API 620?
API 650 F.7.3 mandates that self-supporting roof thickness be not less than that required by API 650 3.10.5 or 3.10.6. Does this mean that the potential non-compliance agreement of API 3.10.2.8 and the Notes located immediately after 3.10.5 and 3.10.6 are inapplicable in this particular usage?
Should the load combinations of API 620-228 be applied to F.7.3 roof calculations?
Must roofs subject to partial vacuum loading in excess of 1" water column and also subject to an internal design pressure of F.1.3 be designed according to API 620 for the external pressure loading as well?
Should design guidance be supplied for self-supported cone roofs subject to API 620 5.10.3.5?
Inquiry 620-I-17/02 indicates that the rules given in API 620 5.10.3.5 are inapplicable for self-supported cone roofs.
Should design guidance for umbrella roofs be provided in API 620?
Although umbrella roofs (API 650 3.10.1.d and V.7.3, among others) are permitted, Inquiry 620-I-05/02 says that there are no design rules given for umbrella roofs in API 620 and that such designs are covered by API 620 1.1. This may be too vague.
Do the requirements of API 650 F.7.2 for compliance with API 620 5.12.4 for dome and self-supporting cone roofs mean that the details of API 620 Figure 5-6 are to be followed for compression-ring roof junctures?
Agenda Item:
Title: /
Design and Welding of Roof Nozzles
Date: / October 2006Contact: / Name: / Bob Hendrix
Company: / Eastman Chemical Company
Phone: / 423-229-3285, FAX 423-229-6099
E-mail: /
Purpose: / To clarify F.7.3 statement "Design and welding of roofs and the design, reinforcement and welding of roof manholes and nozzles shall be in accordance with API 620".
Source: / 650-I-39/00 and Inquiry discussion 5/04 meeting.
Revision: / Initial
Impact: / Unknown
Background: / The extent and applications of the rules are unclear.
Proposal: / Also involves F.7.2. See Below.
Rationale: / Literal reading suggests the proposal.
Notes: / None. This item is new and working. (5/04) Need to review inquiry to determine nature of item. Lieb will investigate. (10/04) Item initially dropped as no information could be found on the nature of the item. Hendrix provided description of inquiry. After further discussion, motion to drop withdrawn. Item remains working. Bob Hendrix volunteered to do this item. (4/05) Hendrix will send out list of issues so that committee can decide whether the standard needs to be revised. (11/05)
This item is misnamed, since the issues are more than just roof nozzles. The original inquiries and responses are listed below.
Inquiry #650-I-39/00
Question
Does the statement of Appendix F.7.3, “design and welding of roofs and the reinforcement and welding of roof manholes and nozzles shall be in accordance with API 620” mean among other things that the materials of construction, fracture toughness requirements, rules of API 620 Section 2.2.2, joint efficiencies, and inspection criteria of API 620 are to be used for F.1.3 steel roofs?
Response
No, an agenda item has been established to clarify F.7.3 statement “Design and welding of roofs reinforcement and the welding of roof manholes and nozzles shall be in accordance with API 620”.
Question
Does the requirement that design and welding of roofs in Appendix F.7.3 mean that the maximum design temperature for tanks in accordance with Appendix F.1.3 be no greater than 250 degrees Fahrenheit as required by API 620 Section 1.2.2?
Response
No
DISCUSSION:
QUESTION / RESPONSEMay only the materials listed in API 620 Section 4 and Appendices Q, R, and S be used in API 650 F.7.3 roofs? / Yes.
If materials other than those listed in API 620 are to be permitted, how are the design allowables to be established? / Not permitted.
Are the maximum allowable stresses to be used in roof design those of API 620? / Yes.
Must the joint efficiencies of API 620 Table 5-2 be applied to the roof? / Yes.
May the radiography examinations of API 620 Section 5.26.4 be used for applicable roof butt joints to achieve a higher joint efficiency? / Yes.
If the maximum design temperature is not limited to 250 degrees Fahrenheit and less as suggested by the response to the second question of Inquiry 650-I-39/00, how is one to modify the material properties in API 620? / Not permitted.
API 650 F.7.3 mandates that self-supporting roof thickness be not less than that required by API 650 3.10.5 or 3.10.6. Does this mean that the potential non-compliance by agreement to API 3.10.2.8 and the Notes located immediately after 3.10.5 and 3.10.6 are inapplicable in this particular usage? / Yes. By specifically invoking the rules of 3.10.5 and 3.10.6, these rules become mandatory and not subject to possible relaxation for this application.
Should the load combinations of API 620-228 be applied to F.7.3 roof calculations? / Yes.
Must roofs subject to partial vacuum loading in excess of 1" water column and also subject to an internal design pressure of F.1.3 be designed according to API 620 for the external pressure loading as well? / Yes.
Should design guidance be supplied for self-supported cone roofs subject to API 620 5.10.3.5?
Inquiry 620-I-17/02 indicates that the rules given in API 620 5.10.3.5 are inapplicable for self-supported cone roofs. / No. Needs to be answered for basic 620 design.
Should design guidance for umbrella roofs be provided in API 620?
Although umbrella roofs (API 650 3.10.1.d and V.7.3, among others) are permitted, Inquiry 620-I-05/02 says that there are no design rules given for umbrella roofs in API 620 and that such designs are covered by API 620 1.1. This may be too vague. / Yes. Needs to be answered for basic 620 design.
Do the requirements of API 650 F.7.2 for compliance with API 620 5.12.4 for dome and self-supporting cone roofs mean that the details of API 620 Figure 5-6 are to be followed for compression-ring roof junctures? / Yes.
PROPOSED CHANGES:
The most relevant sections of Appendix F are extracted from the draft 11th edition of API 650 as posted on the committee website.and the proposed changes are in bold.
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 5.12.4, 5.12.5, and Figure 5-6of API Standard 620, except the allowable compressive stress shall be increased to 140 MPa (20,000 lbf/in.2). No rules are provided for umbrella roofs.
Note: When radial lap joints are included in the compression ring region, see API Standard 620, Section 5.12.2, Note 18, for an important design issue.
F.7.3 The design and welding of roofs and the design, reinforcement, and welding of roof manholes and nozzles shall be in accordance with API Standard 620, including but not limited to, the materials of construction, allowable stresses, joint efficiencies, metal temperature limitations, inspections, and examinations unless expressly overridden by API Standard 650. The thickness of a self-supporting roof shall not be less than that specified in 3.10.5.1 or 3.10.6.1, as applicable, except T shall be the greater of 5.4.2.d or 5.4.2.e of API Standard 620. As an alternative to designing the roof manhole per API-620, an API-650 shell manhole may be used as a roof manhole provided it meets all the requirements for API-650 shell manholes, except that it need not meet the toughness requirements in 2.2.9.
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