DYNOM: Dynamic Underwater Measurement
Authors: Bos A.J. , de Meij M.L. 
Published: October 2008

ABSTRACT
This paper seeks to demonstrate that the Controlled Depth Tow Method (CDTM) of transport and installation of flowlines offers many advantages, but that the sensitivity of the system for environmental conditions and fabrication inaccuracies requires a high level of monitoring capabilities.
The paper reviews the underwater monitoring technology utilised by the international offshore industry during the towage of pipeline systems using the CDTM. Various systems had been developed and applied experiences gained during operations resulted in new combinations of applied technology.
Examples of effects illustrating the importance of reliable systems for monitoring are described.

INTRODUCTION

Objective
The research program DYNOM (1) started with the objective of proving the feasibility of connecting several sensors in an underwater network and transmitting the data to the surface at a very high repetition rate.
DYNOM aims at an improvement in several applications, of which one is the monitoring of towed pipeline bundles.

Methodology
After a thorough analysis of CDTM and bundle monitoring systems, system requirements have been defined where after monitoring techniques are analyzed and tests have been evaluated.

Background
Until 1992 monitoring was carried out using conventional acoustic-systems. In 1992 and 1993 a number of developments have made it possible to achieve considerable improvements. DYNOM aims at further research by investigating several new techniques. In this paper we seek to:give an overview of the effects of certain variables on pipeline tow behaviour.give an overview of the monitoring methodsthe innovations which were useful andidentify innovations which were not useful.
Advantages of the bundle concept and the CDTM method are as follows:simultaneous installation of all lines, with a consequent reduction in installation corridor width, avoiding congestion in field-developmentenhanced protection against physical damagereduced environmental impact and riskreduced corrosion of the internal lines in a controlled environmenta very high degree of quality control during fabricationin general no burial requirementspipeline insulation possibility by gelling of carrier.
Due to these advantages the application of Super Duplex Steel (SDSS), in pipeline construction became more common.
For some hydro-carbon products the acidity can only be combatted using this SDSS, in order to avoid aggressive corrosion. Offshore welding of SDSS is a potential source of problems, delays and cost increases. The offshore related problems can be avoided by adopting the pipeline bundle concept which makes it possible to apply SDSS.
A more recent development is the onshore fabrication and subsequent towage of integrated pipeline systems:
Purpose designed drilling slots or manifolds can be incorporated into the towhead, in order to achieve a reduction in the time schedule required to bring a field on stream and into full production.
Towhead structures of over 200 tonnes weight have been installed using this method, i.e. on the RockWater Elf East Frigg Development Project.