It would get a chance to prove its mettle.

Wet Welding Applications
Structural repairs are one of the most frequent applications of wet welding. The addition of more production-related equipment further loads underwater structural joints at the end of their fatigue life. These joints can be strengthened (or reinforced) by installing shear pups using wet welding techniques.

Anodes may be attached by wet welding to mono-pile structures, eliminating the need for large diameter friction clamps that encompass the entire circumference for conventional attachment.

Minimal structures (decks with no or minimal production equipment) located in areas of the world that have environmental conditions less severe than the Gulf of Mexico are erected in the field using wet welding as a technique to join subassemblies into a structural jacket. For example, Unocal Indonesia and Maxus Southeast Sumatra have installed minimal structures using wet welding techniques.

Conductor guide framing members may require modifications if a new jacket is not stabbed properly over an existing template; or additional wells are to be drilled that exceed the capacity of the existing framing; or a directional angle is desired on an existing slot to reach a hydrocarbon zone below, but at some horizontal distance from the jacket location.

Other applications of wet welding include modifications to existing structures due to a change in operational requirements. For example, adding control umbilical I-tubes to tension leg platform (TLP) hull columns that do not have previously installed appurtenances.

Underwater Surveys
The Eugene Island 273 B deck has two above-water elevations (drilling deck and production deck). There is no cellar deck. The jacket is an X-brace configuration and has four horizontal levels, one at three feet (1m) above mean sea level, and three below: 41 feet (12m), 103 feet (12m), and 186 feet (57m) deep. There are no horizontal braces at the 41-foot (12m) and 103-foot (12m) depths, but there are horizontal X-braces at these elevations.

There are three risers attached to the structure. Two risers are attached to Row 2, which are six-inch risers adjacent to the A2 and B2 legs. A third riser (12 inches in diameter.) is attached to the A1 leg. There are a total of eleven 20-inch-diameter wells installed on this platform that extend from the production deck to below the mudline.

In 2000 a Level III underwater survey, as defined by American Petroleum Institute (API) RP2A, was performed on EI-273B in accordance with requirements of the US Minerals Management Service (MMS) for all operators in US waters. No mechanical structural damage was located. However, three areas of delamination damage were found on structural members by means of flooded member detection (FMD).

The delamination damage was located on the Row 2 side of the jacket, on 24-inch-diameter primary structural members. The specific members were on the B2 side of Row 2, between the 41-foot (12m) and 103-foot (31m) depth points.

A second underwater survey was completed in late August 2001 to further define the total extent of delamination damage in the jacket, gather the metrology of the known lamination damage, perform a detailed survey on the 24-inch diameter stubs, and survey for any obstructions. Base metal samples were collected from the stubs and mid-point joint can for chemical analysis.

The B2 side of the X brace assembly was cleaned of all marine growth and 100 percent visually (VT) surveyed from the 103-foot (31m) depth up to the 41-foot (12m) depth mark. The welds joining the braces to the B2 leg were grit-blasted and magnetic particle (MT) surveyed. No indications were found at either connection.

Three areas of delamination damage were discovered on the lower section of the X-brace between 103 feet (31m) and 72 feet (22m) deep, oriented as a spiralling type of defect with the spiral angle of approximately 45 degrees. The total length of delamination damage was 11.5 inches, with all of the defects clustered together and located just below and within 36 inches of the circumferential butt weld of the 72-foot (22m) joint can. There were no visual or magnetic particle indications on the joint can member.

The upper section (from 72 feet (22m) deep to 41 feet (12m) deep) of the X-brace member on the B2 leg side had a 24-foot-long continuous spiralling delamination indication that initiated from the toe of the weld of the joint can at 72 feet (22m) and spiralled upward 24 feet.

The results of the base metal sample chemical analysis indicated the carbon content (percentage by weight of carbon) and carbon equivalents (CE) were within the ranges qualified by an existing wet welding procedure.

After consideration of various repair techniques for personnel safety during installation, performance, and cost, wet welding was selected as the preferred method for completing the repairs.

Engineering Damage Assessment
The extent of the delaminations of the X-brace members was reviewed structurally to determine if the platform strength was compromised. Since there is no direct analytical method to determine the reduced brace capacity, three separate 3D finite element structural analyses were performed. The objective was to determine if the structure was at risk during Sudden Hurricane Criteria, as recommended by API. The wave height used to generate the hydrodynamic forces was 46 feet (14m).

The three separate analyses performed were as follows:

• Condition 1 - Platform original structural configuration with no members excluded.
• Condition 2 - Platform original configuration, with the vertical diagonal (VD) portion of the X-brace on Row 2 from the 41-foot (12m) mark to the 68-foot (21m) mark excluded from the analysis.
• Condition 3 - Platform original configuration, with the VD portion of the X-brace from the 41-foot (12m) mark to the 68-foot (21m) mark, as well as the VD from the 68-foot (21m) mark to the 103-foot (31m) mark on Row 2 excluded from the analysis.

Replacement braces using scalloped ends were designed to bring the structure back to its original design strength. The maximum stress for underwater welds was limited to 10.5 kilo-pounds per square inch (ksi), based on mechanical testing data from the Welding Procedure Qualification Test Records, which showed a Fy = 51 ksi.

Designing the Repair
When designing structural repairs by wet welding, several factors must be taken into account. One of the first addresses a key limitation of wet welding: overhead welding.

The shielding gases given off by the decomposition of the flux constituents and steam bubbles manifest themselves as a white bubble that block visibility of the diver-welder. A square cut or 4F position fillet weld or groove welds will trap these gasses. Therefore, the lower (or bottom) portion of the weldment should never be square cut with the axis of the weld in the 4F or 4G positions.

Another consideration that must be incorporated in the design is the fact that there will be only one diver-welder at a time working underwater rigging, assembling and fitting up the structural repairs. Everyone else involved in the installation will be on the surface providing support to the diver-welder.

Therefore the assembly procedure must be well-planned to ensure ease of installation and provide the safest possible working environment for the diver-welder.

Repair assemblies (short stubs or longer sections of pipe) are usually attached to doubler plates with all corners having sufficient radius to eliminate corner discontinuities (stacked up starts and stops). The smooth radiuses also reduce stress concentration and hence fatigue potential.

When a replacement member requires installation between two points, a close-fitting, telescoping sleeve assembly will be used that incorporates a fillet weld to join the members together. Square cut tubular members used for the outer sleeve of a telescoping joint are avoided. A square cut member places an immediate limit on the length of the fillet weld joining the two sliding members together. By scalloping the ends, the fillet weld length is increased by 156 percent.

Additional weld length may be added by separating the tangent point between the two arcs of the scallop. The number of lobes used in the scallop design is dependent on the distance to the next member from the fillet weld. Typically, a two lobed scallop design is used because it provides smooth transitions for the diver welder to follow.

X-Brace Repairs
For EI-273 B, the upper B-2 side repair assembly design utilised a doubler plate/pipe stub to connect to the joint can member at the 72-foot (22m) depth mark. The upper end incorporated a scalloped sliding sleeve that had a single lobe at the top and four lobes at the bottom end. The fillet weld size was the same at the top and bottom of the sliding sleeve.

The lower B-2 side repair assembly design incorporated a sliding scalloped sleeve that tied into the 72-foot (22m) joint can member. Due to the short length of joint can available (17 inches, or .43m) at the 72-foot (22m) midpoint, an eight lobed scallop was used at the upper end. The lower end of the sliding sleeve had four lobes. The 103-foot (31m) depth end of the repair member had a single lobe scallop sleeve that stabbed over the remaining stub attached to the B-2 leg.

A qualified wet welding procedure to American Welding Society (AWS) D3.6 and 10 GDMC diver welders were used to carry out the welding operations between depths of 44 and 103 feet (13 and 31m).

Planning and Executing A Safe Job
To ensure that the Safe Work Plan addressed all safety issues associated with the activities, BP sponsored a pre-job safety meeting at GDMC's facility. The purpose of the meeting was to review the job scope, assess risk, and implement any risk-reducing measures prior to starting the job. Representatives from BP (project and operations), GDMC (including the key diving and marine personnel), and third-party safety consultants attended.

The group produced a list of potential hazards to personnel and the environment, including:

• The MV Sea Fox moored alongside the Row 2 side of the structure, near two gas import risers.
• Identifying any intake sumps near the work area.
• Lifting heavy overhead loads. A Job Safety Analysis meeting with the entire crew would precede all lifting activities. Double tag lines to be attached to all loads.
• Lifting tuggers were subjected to vessel motions, causing a hazard to a nearby diver.

To address these points, the vessel location was changed to minimize risk to the risers. Lock-out/tag-out procedures were to be followed to isolate sumps and risers. BP was to provide internal engineering support in the event that a change in lifting locations was needed. Finally, the pneumatic tuggers were positioned on the platform to eliminate vessel motions thus allowing a much safer work location for the divers.

A safe work plan was developed that incorporated the identified hazards and mitigation process for those hazards. Specific safety requirements were addressed (i.e., permit to work, general safety rules, vessel safety, diving procedures, personnel protection equipment). An emergency response plan was developed to meet BP's requirements for ensuring safe hot work. The plan also required another brief pre-job meeting with the full crew just prior to vessel departure. Finally, the specific, step-by-step work plan was developed that included specific safety precautions for each step as required.

The underwater repairs to EI-273B were successfully completed with no changes to the design in May 2002. Fit-up was excellent and the welding was efficiently completed.

It was found necessary during the job to perform quick structural analyses to evaluate changes in lifting locations due to obstructions by platform equipment thus further proving the value of the pre-job efforts.

Following the completion of wet welding activities, all welds were surveyed visually and by magnetic particle techniques. No indications were found on the completed welds.

Then Came Hurricane Lili
On Thursday, October 3, 2002, Hurricane Lili traversed the Eugene Island Area, with the eye of the storm passing about 10 miles to the east of EI-273B.

Lili was, at its peak, a very strong storm with maximum sustained wind speeds reaching 144 mph - a strong Category 4 storm on the Saffir-Simpson scale. In the vicinity of EI-273B, the sustained winds had reduced to 132 mph, although that is still a Category 4 storm.

Extreme wave heights of 56 feet passed through EI-273B - 10 feet greater than the design wave height criteria. The MMS later reported that six older platforms received substantial damage from the storm. Five of those six structures were in the Eugene Island Area, and two of the five either toppled or collapsed with the others leaning over. All the failed structures from Lili were located within a 15-mile radius of EI-273 B.

On January 14, 2003, the MMS issued a notice directing all operators of federal oil and gas leases to conduct a Level II survey (general underwater visual inspection by divers) for all structures within 25 miles of the center of the storm. Preliminary survey reports indicated significant underwater structural damage to several structures in the immediate vicinity of EI-273B.

The Wet Welds Held
Shortly after Hurricane Lili made landfall on the coast of Louisiana, BP performed a Level II underwater survey on the EI-273B structure. All of the underwater members were examined for any storm-related damage. No damage or indications were found.

The entire Eugene Island saga is a great testament to wet welding techniques. Wet welding was used to complete repairs of the damaged primary structural members, and extensive pre-job planning ensured that the repairs were performed in the safest possible manner, on time and within budget.

The wet-welded repairs were then load tested by Mother Nature herself, in the form of Hurricane Lili, a Category 4 hurricane unleashing 56-foot waves, which were 10-feet greater than the designed event loading. After all that, post-storm inspection revealed no damage to the wet-welded repairs.

The wet-welded repairs look even stronger when one considers that six structures within 20 miles of EI-273B were either destroyed or considered a total loss. With its wet-welded braces, EI-273B weathered the storm - a strong testament to the robust capabilities of a properly designed and executed wet-welded repair. UW

Samuel DeFranco and Patrick O'Connor, of BP America, are based in Houston, Texas.

Thomas Reynolds, of Global Divers & Marine Contractors, is based in New Iberia, Louisiana.

Frank Buescher, of Petro-Marine/BCI Engineering, is based in New Orleans, Louisiana.

The authors thank BP's Dr. Jim Ibarra and the Eugene Island personnel for their help in successfully completing this project. This article was originally published by the American Society of Mechanical Engineers in the Proceedings of the 22nd International Conference on Offshore Mechanics & Arctic Engineering.