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API STD 653-2009 pdf free download

API STD 653-2009 pdf free download.Tank Inspection, Repair, Alteration,and Reconstruction.
4.2.3 Floating Roofs Areas of roof plates and pontoons exhibiting cracks or punctures shall be repaired or the affected sections replaced. Holes through roof plates shall be repaired or replaced. Areas that are pitted shall be evaluated to determine the likelihood of through-pitting occurring prior to the next scheduled internal inspection. If so, the affected areas shall be repaired or replaced. Roof support systems, perimeter seal systems, appurtenances such as a roof rolling ladder, anti-rotation devices, water drain systems, and venting systems shall be evaluated for needed repairs or replacements. Guidance for the evaluation of existing floating roofs shall be based on the criteria of API 650, Annex C, for external floating roofs, and Annex H for internal floating roofs. However, upgrading to meet this standard is not mandatory. 4.2.4 Change of Service Internal Pressure All requirements of the current applicable standard (e.g. API 650, Annex F) shall be considered in the evaluation and subsequent alterations to the tank roof and roof-to-shell junction. External Pressure As applicable, the roof support structure (if any), and the roof-to-shell junction shall be evaluated for the effects of a design partial vacuum. The criteria outlined in API 650, Annex V shall be used. Operation at Elevated Temperature All requirements of API 650, Annex M, shall be considered before changing the service of a tank to operation at temperatures above 200 °F. Operation at Lower Temperature Than Original Design If the operating temperature is changed to a lower temperature than the original design, the requirements of the current applicable standard for the lower temperature shall be met. 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. Shell corrosion occurs in many forms and varying degrees of severity and may result in a generally uniform loss of metal over a large surface area or in localized areas. Pitting may also occur. Each case must be treated as a unique situation and a thorough inspection conducted to determine the nature and extent of corrosion prior to developing a repair procedure. Pitting does not normally represent a significant threat to the overall structural integrity of a shell unless present in a severe form with pits in close proximity to one another. Criteria for evaluating both general corrosion and pitting are defined below. Methods for determining the minimum shell thickness suitable for continued operation are given in 4.3.2, 4.3.3, and 4.3.4 (see Section 6 for frequency of inspection).
d) See for minimum permitted values for t 1 and t 2 . The additional loads in shall also be considered. e) The criteria for continued operation is as follows: i) the value t 1 shall be greater than or equal to t min (see 4.3.3 or 4.3.4), subject to verification of all other loadings listed in; ii) the value t 2 shall be greater than or equal to 60 % of t min ; and iii) any corrosion allowance required for service until the time of the next inspection shall be added to t min and 60 % of t min . Widely scattered pits may be ignored provided that: a) no pit depth results in the remaining shell thickness being less than one-half the minimum acceptable tank shell thickness exclusive of the corrosion allowance; and b) the sum of their dimensions along any vertical line does not exceed 2 in. in an 8-in. length (see Figure 4.2). 4.3.3 Minimum Thickness Calculation for Welded Tank Shell NOTE In general, the minimum acceptable thickness (t min ) for an entire shell course is determined using a) with H determined to the bottom of each shell course and the results used as a basis for judging the suitability for continued service for the tank. If locally thinned areas are identified or if specific areas are investigated (such as for a shell nozzle installation), the method of b) may be used to complete the evaluation with H determined for that particular location.

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