API Publ 327:1994 pdf download.Aboveground Storage Tank Standards: A Tutorial
2.1 Proposed Tanks
Figure 2.1 shows that the first decision relates to whether the tank is proposed or existing. While the evaluation steps for a proposed or existing tank may be similar or in some cases identical, the results for a proposed tank provide options that influence design and construction decisions. Results associated with existing tanks may lead to repairs or a change of service conditions. If the tank is proposed, then how does one comply with the API in-service AST inspection STD 653 and RP 12R1? (Note: These two documents will be referred to collectively as the API Standard). The logic diagram shows that the API Standard does influence the proposed design, especially in the important area of bottom selection. If the tank is proposed, then one proceeds along the left side of Figure 2.1. After compiling basic data, the major benefit of the procedure is to provide tank bottom design options. This is an important step. If the owner/operator expects a reasonable onstream time, then the influence of cathodic protection, leak detection, linings, etc., on inspection frequency must be explored. Tank bottom design is based on standards and engineering and economic data. The last box on Figure 2.1 provides a method for selecting a bottom design when several configurations satisfy the API Standard.
2.2 Existing Tanks
The right side of Figure 2.1 shows that the evaluation process for existing tanks is separated into three paths. Tank Bottom and Shell are the two paths which are addressed in this tutorial, and are shown in Figures 2.2 and 2.3, respectively. The decision path for evaluation of a tank roof is beyond the scope of this tutorial. However, Figure 2.1 shows that existing tank roofs may be evaluated per the methods in the API Standard and repaired, altered, or returned to service.
2.3 Tank Bottom Figure
2.2 shows the process for evaluating an existing tank bottom. The first decision is to identify concerns associated with either settlement, corrosion, or both. This identification is determined by a tank inspection and evaluation of the inspection data. If a settlement problem is identified, then it should be evaluated as shown in Section 6.1. If found unacceptable, the problem should be added to the list of repair items. The left side of Figure 2.2 shows the process for evaluating bottom corrosion. The referenced sections of API RP 12R1 and API STD 653, and Section 6.2 of this document provide guidance for this evaluation. When the damaged areas are found to be unacceptable, they should be added to the list of repair items. Aller evaluating all the inspection data, the internal inspection interval must be calculated as described in Section 6.2, (assuming that all repairs are performed). Provided the interval is acceptable, the bottom repairs may proceed. However, if the interval is not acceptable, the bottom must be altered, repaired, or replaced before the tank is returned to service. The procedure to evaluate these options is explained in Section 4 and includes examples.
API Publ 327:1994 pdf download
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