Characteristics of an Underwater Wet Repair Weld Made at -560 ft

Abstract

ABSTRACT An underwater wet repair weld was removed from a structural member of a Mobil Oil Gulf of Mexico offshore platform. The wet weld, made at a depth of 560 feet, was an emergency repair intended to be removed from the structure. The weld was subjected to nondestructive and destructive testing to evaluate its metallurgical and mechanical properties. The results of these tests are discussed in comparison to AWS D3.6-B3, Specification for Underwater Welding, and current literature on the subject of wet welding. INTRODUCTION The requirement for an underwater welded repair presents the operator with a choice between two common methods: either a dry hyperbaric weld or a wet weld. The costs of a platform structural repair using a wet weld are generally lower than those of a dry weld due to the large habitats that must be fabricated and installed using the dry method. However, only the dry method can produce worlds of comparable quality and mechanical properties to a surface weld. In addition to revealing the limitations of the wet welding process, the poorer quality also reflects the fact that wet welding is not as well understood as dry welding. There are numerous proprietary wet welding electrodes in use today each consisting of a base electrode (i.e., E60l3, E70l4, etc.) with some type of waterproof coating. While many structural wet welds have been made in the Gulf of Mexico using these electrodes, the repairs must be designed to account for the reduced mechanical properties (i.e., strength, etc.) of the weld. Wet. weld strength, impact properties, hardness and ductility are still not comparable to those of dry welds. Research has only recently been directed at trying to improve the mechanical properties of wet welds by improving their metallurgical properties. First, though, the industry must gain a better understanding of the metallurgical reactions occurring in the wet welding process. Information in recent literature suggests a way to improve the metallurgical and mechanical properties of wet welds by promoting a high percentage of acicular ferrite in the weld microstructure. Acicular ferrite is recognized as the micro structural constituent giving the highest resistance to cleavage fracture (4). It has been suggested that through a better understanding of the metallurgical reactions controlling the weld metal chemistry, changes to the electrode chemistry that would promote acicular ferrite can be made. A carbon monoxide reaction was found by Ibarra et al. (3) to control the weld metal manganese, silicon, carbon and oxygen in wet welds made with E60l3 proprietary electrodes down to a depth of 160 feet. The metallurgical reactions of the weld made at 560 feet are discussed in this paper. WELDING VARIABLES The shielded metal arc welding (SMAW) process was used to make the 560 foot weld with liB-inch diameter E70l4 proprietary wet welding electrodes. The joint was a V-groove configuration. Welding was done in the flat/horizontal position. A constant current type DC generator with a 600 Amp capacity was used. The current ranged from 150 to 160 amps. The welding depth of 560 feet corresponds to 249 psi or 16.9 bars.