Free from the smoke and noise of the factory floor, divers deliver top-side quality below the surface.
Arc welding, in even its simplest form, is a remarkable and useful phenomenon. But when performed underwater, it moves toward awesome and indispensable. First successfully executed in the 1930s, underwater welding today provides an effective and economical maintenance and repair alternative. Combined with specialized fabrication and construction skills, underwater welding makes projects plausible today that 50 years ago would have been out of the question.
It was more than two decades after the 1911 introduction of the first variable voltage portable electric arc welder that Russian metallurgist Konstantin Khrenov made the first underwater weld in lab tests. The technology developed throughout World War II and was used extensively in Pearl Harbor salvage operations. However, it was not until the 1970s that the first underwater wet welding procedure was qualified to AWS standards and the commercial development of underwater electrodes began. The usual metallurgical considerations of matching electrode to base metal apply. In addition, rods for underwater welding have a waterproof coating.
Underwater welding, in the practical sense, is hyperbaric (elevated pressure), and may be done dry in a sealed chamber at an elevated pressure, dry in an open bottom chamber, or wet, which is to say it is done in the water. Early wet welding was considered to provide only temporary service, according to Pete LeHardy, head of business development for Phoenix International, Largo, Md., which specializes in underwater solutions including welding. “It’s only been in the last 20 years that wet welding has gotten to be more widely accepted,” LeHardy says.
Underwater welding procedures are covered by AWS D3.6, Underwater Welding Code, which until about a year ago had been only a specification. Based on the AWS D1.1 Structural Welding Code, D3.6 contains additional information specific to underwater welding procedures, materials and safety.
An underwater ship husbandry program under the auspices of the U.S. Navy’s Office of Supervisor of Salvage and Diving Director of Ocean Engineering (NAVSEA 00C) has for years taken advantage of underwater welding in lieu of placing ships in dry dock. Working closely with the Navy, Phoenix International frequently performs active fleet maintenance on a variety of ships, especially those on deployment. Some procedures are standard maintenance, LeHardy says, such as bilge keel repairs, which involve wet welding, as well as regular inspection and cleaning. Working with the Navy, Phoenix has helped to develop techniques, procedures and equipment to perform various ship repairs and maintenance without the need to go into dry dock. In October, the welders at Phoenix produced the first ever hyperbaric aluminum weld to an acceptance code.
A special purpose marine project completed this year involved blanking off all the openings to the sea on the USS Midway. The vintage aircraft carrier was the largest ship in the world when it was commissioned in 1945, and is now a museum ship in San Diego. The plan was to have divers wet weld steel patches over all the hull openings normally required on an operating ship, for sonar, water intake and discharge and other purposes. The original drawings showed 265 openings, but divers discovered 54 more in the course of the three-year project, bringing the total to 319.
The hull openings ranged from 8 in. diameter to 4 ft. by 9 ft., with varying degrees of hull curvature surrounding each. To accommodate the great variation, welders used a circular dome patch for round openings and a box patch for square and rectangular openings. Welders precisely sized and contoured each individual patch to match the hull around the opening, then welded it into place.
Because of the higher carbon steel used in the Midway’s hull, Phoenix’s welding department developed a new AWS-approved wet welding procedure, which enabled the use of a more efficient and readily available electrode. Phoenix divers made a total of 2,098 ft. of wet welds, amassing 5,300 hours of safe and incident-free bottom time. The museum remained open throughout the project and the cost was a small fraction of what it would have been to place the Midway in dry dock.
Phoenix International’s underwater solutions extend well beyond welding. Although rarely in the limelight, one of its notable projects involved rehabilitating a badly damaged offshore oil rig. When Hurricane Katrina tore through the Gulf of Mexico in August 2005, it left behind an estimated $81 billion of damage, making it the most costly hurricane in U.S. history. Along the way, it destroyed 47 oil rig platforms and caused extensive damage to 20 others, leaving the region’s oil industry reeling. Just four weeks later, Hurricane Rita, the fourth most powerful Gulf hurricane on record, pummeled the same area, destroying 66 platforms and badly damaging 32 others.
Following Rita, Phoenix International took on the challenge of repairing the underwater portion of a large damaged central platform in 270 ft. of water with a field of smaller platforms feeding it. “The structure was probably 30 or more years old and served as a collector hub for a number of other platforms in the area,” says Ken Elliott, Phoenix International’s welding manager.
The lower half of the underwater portion was sound, but bracing in the upper half was ruined. Elliott and anywhere from 15 to 28 other Phoenix International personnel spent 71⁄2 months rebuilding the portion of the structure from 108 ft. below sea level to 10 ft. above.
“It wasn’t pretty out there,” Elliott says. “When Rita came, the platform got hit by a series of waves that we reckoned to be at least 92 ft. high. It wiped out everything on that platform—all of the production elevations, all of the giant machinery. It moved huge containers with giant generators inside of them—it just wiped that thing out.” The back-to-back storms also twisted the structure itself, wracking it by 31⁄2 degrees.
The crew cut out and removed 84 structural pipes that were broken or cracked beyond repair. Next they installed the six 25-ton replacement frames, custom designed and fabricated onshore then delivered by supply ship to the platform 125 miles out in the Gulf. Each frame was built with slip fit, castellated sleeves that were built in to accommodate the 31⁄2-degree wrack of the platform.
“There’s no straightening any of the wracking, so nothing would go back in accordance with original drawings,” Elliott says. “We put those slip sleeves in to serve a couple of purposes. One was to just give the structure back its integrity, as it sits in its wracked condition. The sleeves also provided adjustment in the triangles when the braces were installed.”
The replacement frames have two 11-ft.-tall leg clamps that bolted onto the platform legs. After the 22 21⁄2-in.-diameter bolts were torqued to more than 12,000 ft.-lbs., the crew pulled up the slip sleeve of each brace member and welded it to a clamp on the horizontal member above.
“We made an interference fit between the jacket leg and those clamps,” Elliott says. “Then we welded out those slip sleeves and she’s now got a permanent, but very stable, 31⁄2-degree list.”
A few surprises
What does it take to be an underwater welder? Many Phoenix divers started welding in industry, LeHardy says. “It’s a lot easier to take a good welder and teach him to dive than the other way around.” And quality welding is paramount. “We tell our customers we provide top-side quality welds underwater,” he says.
In addition to the satisfaction of a job well done, underwater welders also reap some benefits that may not immediately come to mind. “You always breath clean, dry air,” Elliott says, “and you don’t get dirty. Plus, you’re not standing on the floor all day, and it’s quiet.”
One thing that’s not a surprise is how well the Phoenix crews work together. “We are always in communication with each other,” Elliott says. “So you might be welding all afternoon, and just talking to your buddy.” FFJ