The Qualification and Continued Evolution of Reeled Steel Catenary Risers

Abstract

Technip began qualification of reeled Steel Catenary Risers (SCR) back in 1997. Industry had raised concerns at that time over the plastic straining cycles that are intrinsic to the reel lay method and the impact these could have upon the service fatigue life of the girth welds. The qualification programme, therefore, included comparison of reeled welds against virgin welds for a suite of fatigue and mechanical testing including full scale fatigue and fatigue crack growth tests. Reeling was shown to have no discernable impact for the fatigue performance level sought when a controlled SCR fabrication process was adhered to. This provided sufficient confidence that the technology was fit for purpose and led to successful fabrication and installation of the first reeled SCR in 2001. Since then more than 25 have been installed in the Gulf of Mexico, with most projects including full scale weld fatigue test qualification following reeling simulations. This paper includes the following: (a) a summary of the philosophy adopted for qualification, fabrication and installation of a reeled SCR, (b) presentation of the reeled SCR track record and evolution of the technology to include mechanized welding processes (c) a look at ongoing developments targeting even higher fatigue performance, and (d) discussion on the development of fracture mechanics techniques that provide further confidence in the concept and can be used to derive appropriate weld acceptance criteria.

Optimising Reeled Pipe Design through Improved Knowledge of Reeling Mechanics

“…in excess of commonly proposed fatigue design curves such as API X' or the UK E classification, as illustrated by Figure 10 [26,27]. Qualification data on the latest projects further shows that BS7608 [29] Fatigue Class D has been met and suggests that C/2 is achievable [28]. Qualification data on the latest projects further shows that BS7608 [29] Fatigue Class D has been met and suggests that C/2 is achievable [28].…”

“…Since then, Technip have installed in excess of 25 SCRs and own a dataset of over 240 full-scale fatigue tests, consistently demonstrating that post-reeled fatigue performance requirements are met, i.e. Improvements in reeled pipeline fatigue behaviour includes attention to the following i) a good control of internal pipe surface across a weld, ii) implementation of high performance welding techniques, prone to low defect level and good root profile, iii) weld cap removal by careful grinding [28]. Improvements in reeled pipeline fatigue behaviour includes attention to the following i) a good control of internal pipe surface across a weld, ii) implementation of high performance welding techniques, prone to low defect level and good root profile, iii) weld cap removal by careful grinding [28].…”

“…The ECA procedures will always conservatively predict some level of tearing to occur but in reality, as flaw sizes get smaller, the crack driving force will not be sufficient to cause flaws to tear [28]. It is also worth pointing out that because of the initially small acceptable defect size, primarily governed by in-service behaviour, the actual growth experienced as a result of reeling will be very small.…”

A Discussion of Practical Aspects of Reeled Flowline Installation

“…In cases where pipe sorting or fit up cannot achieve the desired outcome or where the operational requirements need improved fatigue performance, the pipe end internal machining or counterboring is performed. Typical example that Client is insisting on counterboring are reeled SCRs (see [12]). Limitation of the counterboring machines and the extent it can be performed is an important factor that has to be defined during the design phase.…”