Journal Infrastructure and Built Environment Infrastruktur dan Lingkungan Binaan
Vol. IV No. 2, December 2008
Calculation of Concrete Ballast Requirement for Sub-Sea HDPE Pipeline Krisnaldi Idris 1
ABSTRACT
Marine application of High-density polyethylene (HDPE) pipeline has been used increasing for both industrial and municipal needs, selection of this material especially based on its superiority to corrosion, its wear resistant properties, and simple construction method. The light weight material requires ballast weigh to restrain the pipe against buoyancy and h ydrodynamic forces. Practical recommendation for concrete ballast dimensional selection and its installation requirement had been proposed on several handbook or catalog. However, for important marine application, concrete ballast selection should be determined based on applied hydrodynamic loads, on both pipeline and the concrete ballast. This study applied current hydrodynamic loading calculation method for “small” structure which is adapted to HDPE pipeline and concrete ballast physical condition, during installation and operation. Recommended practice and requirements, requirements, for oil and gas sub-sea pipelines had been studied, studied, thus, hydrodynamic force calculation is conducted based on selected applicable wave theory, hydrodynamic coefficient for pipeline and concrete ballast are selected based on their physical condition. The required concrete ballasts are computed for four load cases. cases. An iterative procedure must be developed to considered hydrodynamic loads on both, pipeline and concrete ballast. Computation results show importance of selecting a proper concrete ballast weight. Key words: HDPE pipeline, on bottom stability
I. INTRODUCTION
High-density polyethylene (HDPE) pipeline has been used for both industrial and municipal applications, especially due to its corrosion free characteristic and its wear resistance ability. Properties of HDPE pipe have made it very well suited for marine applications. Since HDPE pipes have a density lower than water, they must be weighed down to compensate for buoyancy force and to withstand lateral hydrodynamic forces. Units of concrete ballast are regularly used as a weigh, units are designed symmetric to the centre of the pipe and the pipeline will be placed approximately one-quarter of its diameter above the sea bottom, as illustrated on Figure 1. Increasing application of HDPE pipe in marine environment require adequate concrete weight design which is able to withstand hydrodynamic hydrodynamic force (due to wave and current) and ensure vertical stability and lateral stability of the line. Table 1 shows several important properties of HDPE material.
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Table 1 Typical properties of HDPE
General Property Specific gravity Tensile Strength at yield Elongation at break Modulus of Elasticity Elasticity
Value 950 – 965 18 – 24 >600 400 – 1000
Unit kg/m3 kg/cm2 % N/mm2
HDPE pipe Concrete Ballast Unit HDPE pipe Concrete Ballast Unit Figure 1 HDPE pipeline and concrete ballast units
Research Groups of Ocean Engineering, Faculty Civil and Environmental Engineering, Institut Institut Teknologi Bandung, rd Lab. Tek. VI 3 Floor, Jl. Ganesa No. 10 Bandung, 40132, e-mail:
[email protected] [email protected]
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Krisnaldi Idris
