Comparison between ASME Analytical Calculation and FEA Calculation for the Design of Mid Water Arch Tank and Structure

Before I start my presentation, I would like to present to you the flow of my presentation today. Firstly, I am going to give a brief introduction on MWA Tank and Structure. After that, I will be focusing on each and every component of a typical MWA system, which are buoyancy tank and structure such as gravity base, gutter and bulkhead. Then, I will be explaining on the structural assessment methods use to assess the structure integrity of a MWA system, which are ASME Analytical Calculation and FEA Calculation. Then, I will be comparing the result obtained from these two structural assessment methods. Last but not least, I will be concluding this presentation by state the reason why we plan to go for FEA Calculation while designing a MWA tank and structure.

Part 1: Overview of MWA System

Mid Water Arch system is a buoyant subsea structure that is tethered on the mean sea level by certain amount of buoyancy force as shown in the diagram.

MWA system is designed to support an array of flexible riser and umbilical as shown in the diagram. In normal cases, MWA is used to achieve “S configuration”, which are lazy S and steep S configuration. MWA is also applied to protect the integrity of the support flexible riser and umbilical.

MWA Description

Mid water arch is a system made of buoyancy tank, gutter, bulk head and gravity base. As you can see from this diagram, a typical buoyancy tank of the MWA is normally in cylindrical shape with two ellipsoidal heads. There are two types of gutters designed in an arch system, which are horizontal gutter, which is designed with certain radius in order to ensure that the bending radius of the riser when the riser lay down on it is always greater than the minimum required bending radius. Whereas, the vertical gutter is designed with certain spacing in order to allow the riser to lay down on it in a fixed and correct position to avoid clashing happens during operation. A gravity base is designed to be the foundation of the MWA and allow it to stay at a fixed position. Lastly, the anodes applied on the MWA a system is normally use for catholic protection to avoid corrosion happens on the MWA system during the design life period.

MWA, Tether and Tether Base General ArrangementA MWA system is normally tethered to the seabed by a gravity base as shown in this diagram.

Structural Assessment of MWA tank and structure

Structural Assessment of the MWA tank and structure is normally performed during the design stage in order to ensure that the MWA system design is able to well perform throughout the design life. Therefore, analysis while various types of load conditions applied on the tank have to be performed. In today presentation, there are two types of structural assessment of MWA tank and structure are going to discussed, which are ASME Analytical Calculation and FEA Calculation. ASME Analytical Calculation is used commonly in Technip to assess the structural integrity of the MWA tank and structure up to today. Whereas, FEA Calculation method is commonly uses in other marine structure such as subsea clamp. Therefore, in this study, FEA Calculation is chosen to assess the structural integrity of MWA tank and structure. The pros and cons of each method will be discussed in the following slide.

Pros and Cons