The installation of flowlines in ever deeper and remote areas requires the usage of specific technologies in order to carry out pre-commissioning operations. As the water depth increases, the weight of the conventional equipment to be deployed to perform the required operations becomes a major issue and alternate solutions are thus required. An option lies in using Coiled Tubing. Coiled Tubing consists of continuous pipe that has been coiled around a reel and can be deployed and recovered according to operational needs. So far, offshore operation of coiled tubing has been limited to small diameters and to short operational duration. The pre-commissioning operations can require the Coiled Tubing to be deployed several times for durations sometimes exceeding a month, and also requires larger diameters (typically 3.5"). As the duration of operations increases, a suitable way of assessing and mitigating the fatigue of Coiled Tubing is required. To that extent SAIPEM has carried out an extensive testing campaign aiming at better understanding the mechanism underlying plastic and elastic fatigue. Once enough confidence in the models has been gathered, the Coiled Tubing has been deployed offshore for the pre-commissioning operations of several Brazilian projects. This paper reports the lessons learnt from an innovative pre-commissioning method based on Coiled Tubing that was successfully implemented on four ultra-deep offshore pipelines in 2015. All these projects were located offshore Brazil in water depth around 2200 m. The paper will provide feedback on the engineering and operations associated with the use of large diameter Coiled Tubing for pre-commissioning in deep water. A first section will highlight the specificities of the projects while subsequent sections will provide more details on offshore operations.