Design And Operational Considerations For Unsupported Offshore Pipeline Spans

Abstract

Desfgn and operational considerations have been examined in determining the significance of unsupported offshore pipeline spans that may develop during pipeline installation or during field operation, Allowable unsupported span lengths determined during the design phase are generally based on the strict code compliance and the design baais encompassing the worst possibilities of the environmental and operational loads. During operation unsupported spans, however, do develop beyond the allowable limits, perhaps due to various unforeseen local conditions. Applying original design criteria is likely to result in cost prohibitive repair predictions, while lack of action may result in loss of production or other concerns.Without violating the design code requirements of an existing or a proposed pipeline system, realistically safe design can be approached by evaluating the sensitivity of the key design parameters.Remedial repair priorities of the unsupported spans can be established for the pipelines in service while recognizing operating constrains, budget and schedule. Based on periodic survey, properly formatted data of the survey and reanalysis of the design parameters, pipeline span repair cost estimates and schedule can be appreciably reduced.Similar principles can be applied to a pipeline in planning and design stages in order to ensure a safe operating design and to eliminate an uneconomically conservative design. These design and operational considerations are illustrated through a case study of work recently carried out.

Analysis on a Cast-Iron Pipe Applied to Protection of Underwater Cable

“…The risk for the electricity power cable exposed in seawater includes the environmental hazards and threatening of human operation in ocean. Environmental hazards could be ranged from the regular ones such as the water pressure, possible corrosion, erosion and abrasion from sand and debris action under sea to the major hazards like huge storms, earthquakes and tsunamis et al [1,2,3,4] Most cable systems are able to resist the regular threatening but for the major hazards [5,6], special design based on the degree of the natural hazard must be applied. As for the threatening of human being activities such as the possible damage from ship anchoring or fishing operation, especially an impact loading or dragging exerting on the cables, it will be very dangerous and may cause serious damages.…”