ANALYSIS, PREDICTION, AND REPAIR OF VERTICAL WAVE FATIGUE DAMAGE OF CONDUCTOR GUIDE BRACING

Fatigue damage has been discovered in the conductor guide bracing of many of Mobil's Gulf of Mexico offshore platforms in water depths ranging from 62 to 432 feet. The damage varied from magnetic particle indications to total failure of the guides. Although the damage was found primarily in the uppermost underwater guides, cracks have been discovered in elevations as low as the -225 foot level. Inspection and analysis revealed the cause to be fatigue due to vertical wave loading. Although generally ignored in the past, vertical wave loading is now recognised as a major factor in conductor guide placement and design. The paper will discuss a simplified fatigue analysis method and various repair methodologies including weld profiling, internal grouting of members, removal of guides, bracing of guides, and the installation of stress grouted clamps. Twenty-eight multiwell drilling / production platforms were analysed. They were all modern designs installed from 1972-1989 and ranging in water depth from 62 to 760 feet. Potential fatigue life problems were discovered in 23 of the 28 platforms analysed, indicating that a problem exists in the current method of designing and placing conductor guides. An analysis method is presented that can predict potential fatigue damage before it occurs and without costly inspection methods. Economical repair methods are proposed that can be implemented before fatigue cracking occurs, resulting in significant savings in maintenance costs. This paper also includes guidelines for designing and placing conductor guides on new platforms.

• Supplemental Notes:
  • OTC 91, 23rd Annual Offshore Technology Conf; 6-9 May 1991; Houston, Tx, USA. Procs. Vol 3, Ppr OTC 6653, p 67 [11 p, 25 ref, 2 tab, 5 fig]
• Authors:
  • Lang, G R
  • Critz, B L
  • Salter, H J
• Publication Date: 1991

Language

• English

Subject/Index Terms

• TRT Terms: Cracking; Fatigue (Mechanics); Offshore structures; Repairing
• Uncontrolled Terms: Fatigue life
• Old TRIS Terms: Wave loads on structures
• Subject Areas: Bridges and other structures; Marine Transportation;

Filing Info

• Accession Number: 00701412
• Record Type: Publication
• Source Agency: British Maritime Technology
• Files: TRIS
• Created Date: Aug 14 1995 12:00AM