Reliable Lashing Lines Fatigue Monitoring for a Tender-Assisted Drilling Unit

Prislin, Igor (BMT Scientific Marine Services Inc.) | Chabot, Luc (Murphy Sabah Oil Co. Ltd.) | Dean, Linda H. (BMT Scientific Marine Services Inc) | Liu, Tuanjie (OffshoreTech, LLC) | Ye, Wei (Offshore Tech LLC)

OnePetro 

Description of the Proposed Paper:
The paper describes a reliable, effective, and practical, solution for monitoring and reporting fatigue damage of lashing lines on the Murphy Kikeh DTU. The solution is based on a ton-cycle method that uses measured line tension and calculated number of cycles when the critical line segment enters and exits the sheave. The method is calibrated using real data and then implemented on-board of the DTU. It provides indication of the integrity endurance level of a critical lashing line. The same method helped in re-designing the original lashing system, which reduced wear and prolonged the fatigue life by a factor of four.
Application:
The integrity and the fatigue life of the lashing lines that keep TAD unit closely connected to the DTU is carefully and continuously monitored by the Integrated Marine Monitoring System.
Fatigue life of a line is monitored through cumulative ton-cycle value. When this value approaches the calibrated threshold, the line can be replaced at the most convenient time, avoiding unpleasant surprises such as when a line breaks during production, making the production safer and more cost effective.
Results, Observations, and Conclusions:
The lashing line ton-cycle method has been integrated with the other marine and structural monitoring parameters on board of the Kike DTU for several years. . When the values approach the 100% of the absorbed fatigue life, the results are displayed on the operator screens in the control room indicating that the line is in a critical condition with a high expectation to break. This indication helps the operator to plan, prepare and conduct the line maintenance or replacement in a timely manner and at the most convenient time without interrupting critical phases of operation. This process became a standard process for the lashing line integrity monitoring and maintenance and it has been working reliably for more than three years.
Significance of Subject Matter:
Developed and implemented ton-cycle method shows a simple yet effective and reliable method for increasing overall the safety of operations, as well as preventing costly interruption of normal production on the Kikeh DTU and the nearby TAD unit.