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Pipeline Technology Journal 2-2015

Latest developments and news from the pipeline industry

RESEARCH / DEVELOPMENT / TECHNOLOGY 40 PIPELINE TECHNOLOGY JOURNAL ECA CONCEPT The concept of performing the ECA is shown in Figure 3. Fracture, plastic collapse and fatigue limit states were considered in the as- sessments. As can be seen in the flow diagram (Figure 3), the limiting envelopes for fracture/ plastic collapse limit states are first estab- lished (peak loading) for each condition (installation, as-laid, and op- eration conditions). They represent limiting flaw length by flaw height values in girth welds. If such values are not exceeded, the pipeline can sustain maximum peak loads with minimum risk of fracture/ plastic collapse. Fabrication flaws may grow to larger dimensions due to fatigue dam- age associated with variable loading during the design life. For the purpose of the ECA, fatigue growth due to variable loading is estab- lished at all stages of the design from weld fabrication to potential decommissioning. Consequently, the flaw size at end of every stage was assessed to comply with limiting conditions established by frac- ture/ plastic collapse assessments. The above approach is considered for Hejre pipelines ECA and typi- cal results are presented in the following section. 6. ECA RESULTS Typical examples of theoretical surface breaking flaw dimensions es- tablished in the ECA are presented in Figure 4 to Figure 7 below, for both Export Pipelines (Oil and Gas) and both fatigue regimes (“Nor- mal” operation and “Reduced” operation). The solid lines in the graphs represent limit states for fracture/ plastic collapse associated with installation and operation conditions. The As-Laid condition is omitted from the graph, since it is not critical. Figure 3: Saipem Ltd’s ECA Concept 12” OEP laydown checks

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