Common question welding storage
Below some common question and answer about Welded Steel Tanks for Oil Storage
as per API 650 :
as per API 650 :Question : Does API 650 provide a way to obtain a frangible roof connection on a small tank describe as follows? - Diameter: 8 ft. - Height: 10 ft. - Cross sectional area of the roof-to-shell junction "A": larger than that allowed by the equation in Section 3.10.
Answer : No. The API Subcommittee on Pressure Vessels and Tanks is currently reviewing the design criteria for frangible roof joints. You may wish to review Publication 937, Evaluation of Design Criteria for Storage Tanks with Frangible Roof Joints.
Question : Section 10.4.3 states "When considering dead loads only, including the weight of the rafters and the roof plates, the compression flange of the rafter shall be considered as receiving no lateral support from the roof plates and shall be laterally braced if necessary (see Section 3.10.4.2)." This statement, which is a fairly recent revision, imposes much more stringent requirements on the rafters than what was required in the earlier editions that allowed the assumption of lateral bracing from the friction with the roof plate. What was the basis for this change in requirements?
Answer : API does not respond to questions seeking the rationale for requirements in its standards. These requirements are based upon consideration of technical data and the judgment and skill of experienced engineering and technical personnel representing both users and manufacturers who serve on the standards-writing committees. All technical meetings during which API requirements are considered are open to the public. The API Pressure Vessels & Tanks Subcommittee, which is responsible for this standard, meets twice per year at the Spring and Fall Refining Meetings. Information on these meetings can be found on the API website at www.api.org/events.
Question : When installing girders and rafters in an existing tank, do they need to be installed in accordance with the latest edition of API Standard 650?
Answer : Yes, refer to API Standard 653, Section 9.11.1.2.
Question : When not altering the roof rafters and framing of an existing tank, is it necessary to upgrade it to the current edition of API Standard 650?
Answer : Refer to API Standard 653 Section 4.2.2
Question : Referring to 3.10.1(a) and 3.10.2.3, is it permissible by the code to locate rafters outside the tank over the roof plates? The rafters would hold the roof plates welded to its bottom flange instead of supporting the plate.
Answer : No, however, a committee agenda item has been approved that will change this requirement. Please refer to the next addendum of the standard.
Question : What does API 650, Section 3.10.2.5 mean by the term "top angle"?
Answer : Angle refers to a steel angle structural shape - see the AISC "Manual of Steel Construction" or other similar publications. It is usually a 90 degree shape but can be other angles. The "top angle" is the structural angle, purchased or fabricated, that is located at the top of the shell .
Question : Can the roof plate be attached to the top angle with a groove weld on top and a fillet weld on the inside?
Answer :No
Question : Refer to API 650, Section 3.10.2.5.1 and Figure F-2. Is the area "A" the crosshatched area in Figure F-2?
Answer :Yes
Question : Are roof support trusses which are welded to the shell acceptable?
Answer : API doesn't provide design detail attachment of roof trusses to the shell. Please refer to Section 3.10.2.7.
Question : In section 3.10.5 for self-supporting roofs, may the corrosion allowance be added to the minimum calculated thickness given by tmin = D/400 sin Ø to arrive at a total minimum required thickness of 3/16 in. or greater?
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