A protection frame is urgently needed by subsea hot-tap tee and its control valve in shallow water subsea engineering to against the fishing gear and dropped object. And the hot-tap protection frame can also be used as an installation assistant for the hot-tapping tool orientation and operation. Control valve observation and operation is easier for diver or ROV outside the protection frame. This paper presents the design consideration of subsea hot-tap protection frame and indicates some problem during fabrication, transportation and installation. A typical design example is also be demonstrated in this paper.
Hot-tapping technology is widely used in technical transformation at a certain position of pipeline during production process. In case of leakage, blockage and corrosion of the pipeline, hot-tapping on pipeline is necessary to add auxiliary lines to maintain production and replace the faulty pipe section.
In recent years, with the continuous increase of drilling and production capacity, the scale of subsea pipeline network is increasing day by day. Through comparison, it found that hot-tapping is the most economical choice for connecting the new pipeline to the old one. To facilitate pre-commissioning of new pipeline, control valves on it are necessary. According to ISO 13628-15, for subsea equipment in depths less than 750m, the influence of fishing gear and dropped object should be considered. And for equipment in depths below 750m, normally accepted as guideline-less, bottom trawling is less common. For locations where it can be documented that no bottom trawling occurs, and is not likely to occur within the design life of the installations, the equipment need only be protected against dropped objects. Therefore, in any case, a protection frame is very useful for the security of hot-tap region.
Convenient for hot-tapping operation and the new pipeline accessing, a T-shape trench should be dug in advance. But the trench will make more difficult for protection frame design and installation. And it also brings a lot of consequences for the determination of hot-tapping location and the support for the control valves on new pipeline. So the subsea hot-tap protection frame needs to have the auxiliary functions such as assistance for hot-tap tool lowering and positioning, control valve support, etc.
