Fabrication of the Baldpate Compliant Tower
Authors: Edel James C. , Thibodeaux Stephen , Sezer Fuat , Payne Jack D. , Willis Charles H. 
Published: October 2008

The Baldpate compliant tower, built by operator Amerada Hess Corporation (AHC) and 50% joint-interest owner Oryx Energy Company in Garden Banks block 260 in the Gulf of Mexico, is the first free-standing, non-guyed compliant tower. This paper describes the fabrication of the tower and discusses special problems associated with fabrication.

Introduction

The Baldpate compliant tower, in 1,648 ft of water, measures 1,900 ft from the flare tip to the seafloor. The tower is a 19-slot drilling/production platform set over a 9-slot drilling template, has production facilities for 60,000 BOPD and 200 MMSCFD, and supports two steel catenary export risers and a steel catenary bundled-flowline riser. The tower was installed in the spring of 1998.

The tower has four basic structural components (Fig. 1): skirt piles, the jacket base section (JBS), the jacket tower section (JTS) and the deck. Loadout weights for these were approximately 5,600 st, 9,000 st, 20,000 st and 4,000 st (2,400 st structural), respectively. This paper focuses primarily on the fabrication of the two jacket sections, which were built at two different locations in Texas and Louisiana. Although neither the JBS nor the JTS was particularly heavy compared to single-piece jackets on several other projects, there were unique aspects to the fabrication of each section.

This paper discusses fabrication challenges and other aspects of the project relating to fabrication: the specification of steels; fabrication schedules; large-diameter members; large miter joints; a removable launch cradle; dimensional control; erection sequences; and the control of deflections during loadout. A special challenge was the splitting of the jacket fabrication between two contractors.

In addition to basic information about the fabrication effort, this paper will dwell on new or unique aspects to the fabrication and preparations for it, and on topics of general interest related to the execution of large projects. Similarly, while the focus of this paper is on the unique jacket, some information on the fabrication of piles and deck is included, as these components also involved major fabrication efforts.

This paper will first address general issues, and then the fabrication of individual components. In discussion of the former, emphasis will be placed on the perspective of the operator; the latter will reflect more that of the fabricators.

General Fabrication Topics

This section of the paper will focus on issues common to both sections of the jacket.

Steel Specifications.

The steels used on Baldpate were similar to those used on several other large platforms built in the last decade: all the jacket steel was high strength (50 to 60 ksi) and much of it was the so-called micro-alloyed steel covered by the API 2Y and 2W specifications. The axial tubes in the jacket tower section (JTS) were all 60 ksi API 2Y steel. In addition, about 500 st of the JTS, that is, much of the steel used in its launch cradle, was API 2MT1 steel; this was used as a less-expensive alternative to API 2H steel, but nevertheless excellent weldability and toughness properties are a feature of this steel. A far larger amount, some 5,000 st of 2MT1 steel, was used in the skirt piles. The Baldpate platform is believed to constitute the first use of 2MT1 steel.

AHC, recognizing early in the project that the experience of other oil companies needed to be utilized, secured the right to use specifications developed by another operator and used earlier on two major platforms. The specifications were subsequently updated by AHC, with the aid of metallurgical and welding consultants, to incorporate newer developments in steel technolo