Effective Utilization of Titanium Alloys in Offshore Systems
Authors: Schutz R.W. 
Published: October 2008

Titanium alloys offer a unique combination of high strength, low modulus, excellent seawater toughness/endurance limits and superior resistance to seawater and produced fluids, making them the technically correct material for numerous offshore components. These attractive properties and practical material and design aspects are reviewed in relation to current and candidate titanium alloy applications offshore outlined in the paper.

INTRODUCTION

The search for new vast hydrocarbon reserves to replace and augment existing reserves has led oil/gas producers into deeper waters offshore. Although deeper water activity is stimulated by and becomes more justifiable as oil/gas prices increase, it has been the development and availability of improved drilling and subsea well production technology that defines the window of available reserves. Offshore systems capable of operating in water depths of 2400 meters have been projected by the year 2000',

As water depths exceed approximately 310 meters, floating-type product ion systems become favored economically over the gravity-based systems. Common floating systems include semi-submersibles (see Figure 1), tension-leg platforms TLP), and drillship. Highly critical aspects of floating systems include weight (center of gravity), available topside deck space, and, as with all offshore systems, high cost penalties associated with maintenance and downtime. These requirements specifically favor the consideration and use of titanium alloys, based on their superior corrosion resistance and strength to density (light weight) characteristics, The unique synergistic combination of these properties with low modulus (high flexibility) and excellent air/seawater endurance limits often make these alloys technically correct for numerous stat is and dynamic offshore applications.

Despite their obvious benefits and a growing and established favorable service record in hydrocarbon processing, production, and offshore systems, significant user and designer misperception and apprehension related to the fabrieability, field weldability, cost, availability, hydrogen resistance, and galvanic compatibility of titanium alloys in offshore service still exists. It is the intent of this paper to address and dispel these concerns by furtherincreasing user/designer familiarity with relevant titanium alloy mechanical, physical and corrosion properties, and offering basic design criteria andguidelines for specific component applications. A brief overview of existing and future prospective applications of titanium alloys in offshore hydrocarbon production is also provided.

INCENTIVES FOR UTILIZING TITANIUM ALLOYS

The basic characteristics of titanium alloys which synergistically motivate their use on offshore production pledforms and subsea systems include:Family of alloys offering a wide range of strengthsAttractive mechanical propertiesUnique combination of physical properties, particularly low modulus and densityHigh strength to density ratio to achieve light weight structuresSuperior corrosion and erosion resistance, especially in seawater, marine, and hydrocarbon product ion environmentsGood fabrieability and weldabilityReasonable cost and availability