Repair and Connection of Offshore Pipelines In Water Depths to 3,000 Feet

Abstract

Pipeline laid in waters beyond the practical working depth of divers Pipeline laid in waters beyond the practical working depth of divers is no longer unheard of. A concept for the in-situ connection or repair of pipelines in depths to at least 3400 ft is described. The design objectives include the elimination of the need for divers, an insensitivity to depth and surface conditions, and the use of existing and proven components. Introduction In the near future, submarine pipelines laid in water beyond the practical working depth of divers will become a reality. The offshore oil industry is in a period of accelerating growth. A large percentage of the remaining undiscovered petroleum reserves is believed to be beneath the waters of the continental shelves and slopes. Offshore expansion is expected to continue into those ever-deeper waters. Exploratory drilling has already moved into water thousands of feet deep. Several major programs have been announced for development of production equipment for the fields that are to be production equipment for the fields that are to be produced in these water depths. With production produced in these water depths. With production will come the need for flowlines, transfer lines, and trunklines to shallow-water facilities or to shore. Much of the technology required to design and construct deep-water pipelines has already been developed. Many of the concepts have been verified in actual construction operations in present water depths. The nonroutine operations, such as sea-floor connections, general maintenance, or pipeline-damage repair, have not received the same attention. The forces of nature and the activities of man may expose any underwater structure to the risk of damage. In the case of the submarine pipeline, this damage might be expected to take one of the following forms:minor deformation of pipe cross-section,leak or failure caused by pipe defects,leak caused by corrosion,buckle or collapse of pipe, andbreak or separation of pipe. pipe. The risk of damage to the pipe during construction can be greatly reduced by improved design and construction methods now available. Pipe defects may be avoided or detected before installation by careful specification of pipe, backed by a program of supplemental nondestructive pipe, backed by a program of supplemental nondestructive testing. Corrosion leaks can be virtually eliminated (as evidenced by experience with existing major offshore pipelines) by applying coatings, using sacrificial anodes, pipelines) by applying coatings, using sacrificial anodes, and applying impressed-current cathodic protection. However, it can be assumed that any pipeline installed in an area of difficult sea-floor conditions, heavy-gear trawling, or marine construction will be exposed to the risk of damage. If it is also assumed that any lengthy interruption of service on a trunkline will result in shut-in production or interruption in supply to customers, the need for a method to minimize the down-time during repairs is obvious. A very limited number of repair methods are available for use in relatively shallow water but, in most instances, these rely on a combination of extensive use of divers and a heavy lift capability at the surface. No method of repair has been demonstrated for use in depths beyond the reach of divers, and only a very few have been proposed. Several years ago, in anticipation of the need for large-diameter pipelines in very deep water or in areas in which environmental conditions limit the effectiveness of existing procedures, an investigation of deepwater pipeline repairs was undertaken. pipeline repairs was undertaken. JPT P. 415