October 15-17, 2024 at Orange County Convention Center in Orlando, Florida
FABTECH Shows ▶
Register
An info icon
A close icon

Join Us in Orlando

Attend Exhibit

Expo Hours

Tuesday Oct 15 9 AM — 5 PM
Wednesday Oct 16 9 AM — 5 PM
Thursday Oct 17 9 AM — 4 PM

Venue

Orange County Convention Center

9800 International Drive
Orlando, Florida 32819

About the Expo

North America's largest metal forming, fabricating, welding and finishing event heads to Orange County Convention Center in October 2024. FABTECH provides a convenient "one stop shop" venue where you can meet with world-class suppliers, see the latest industry products and developments, and find the tools to improve productivity, increase profits and discover new solutions to all of your metal forming, fabricating, welding and finishing needs.

A search icon

North America's Largest Metal Forming, Fabricating, Welding and Finishing Event

From the Blog

Staying the Course during Underwater Repairs

By Jennifer Dallos on on
Underwater wet welding was used to permanently repair a crucial part of a vessel’s propulsion system By Uwe W. Aschemeier, senior welding engineer and Kevin S. Peters, director of technical sales & Asia-Pacific operations, for Subsea Global Solutions, Miami, Fla. Reprinted with permission: The AWS Welding Journal In the maritime world, a propulsion system is defined as a unit used to provide thrust to enable a vessel to move across water. Mechanical marine propulsion systems consist of electric motors or engines that turn propellers. After ships had been moved by paddles and sails for centuries, marine steam engines were introduced, making them the first engines used in marine propulsion. Steam engines have since been replaced in modern ships by diesel engines and gas turbine engines on faster ships. Electric motors fueled by electricity stored in batteries provide energy-efficient propulsion for submarines and electric boats. Liquefied natural-gas-fueled engines also provide economic advantages and low emissions. Propulsion systems that are in use today, or are in a research state, include diesel, wind, nuclear, gas turbine, fuel cell, solar, steam turbine, diesel-electric, waterjet, and gas fuel propulsion. Propulsion systems often require repair from damage as a result of loads and stresses, such as severe weather and erratic maneuvers. The following story describes the permanent repair of a crucial component on a cruise ship’s propulsion system using underwater wet welding techniques. To keep the ship en route, the repair was performed during regularly scheduled port stops without interrupting the vessel’s itinerary. A Damaged Skeg Following its departure from Miami, Fla., a cruise ship experienced a grounding, which is the impact of a ship on the seabed or waterway side. After being contacted, Subsea Global Solutions (SGS), an underwater ship maintenance and repair provider, deployed a dive team to inspect the damage during the ship’s next port of call in the Caribbean. The inspections discovered the starboard Azipod® skeg was torn off just below the weld between the skeg and the cofferdam at the interface to the Azipod gear housing. The Azipod is a marine propulsion unit consisting of a fixed pitch propeller mounted on a steerable gondola (the pod). The pod contains the electric motor driving the propeller. A fin (skeg) is usually mounted underneath the pod to increase maneuverability and fuel efficiency; this is the part that was torn.   However, the skeg was not completely torn off the cofferdam bulkhead, as the skeg material was still connected in some areas to the bottom plate of the cofferdam underneath the gear housing of the Azipod. The cofferdam and the associated weld joint between the cofferdam and the gear housing of the Azipod were undamaged. Proposed Repair Solution Before beginning the repair, an extensive document was created describing the planned approach. It listed all necessary documentation required to facilitate an underwater wet weld repair, including welder qualifications, procedure qualification records, welding procedure specification, and chemical analyses of materials to be welded. After the vessel’s owner and the original equipment manufacturer (OEM) of the Azipod agreed to the proposed repair approach, the next step was to submit the detailed repair procedure to the ship’s classification society for review and approval. Classification societies are nongovernmental organizations that establish and maintain technical standards for the construction and operation of ships and offshore structures. The proposed solution involved a permanent repair of the damaged skeg by removing the remaining skeg plating, including the weld joints, from the cofferdam using hydrogouging, as well as installing a new skeg by employing underwater wet welding techniques and procedures approved by GL (now DNV GL) to Class A in accordance with the American Welding Society (AWS) D3.6M, Underwater Welding Code. The repair was scheduled during regular port stops without interrupting the itinerary of the vessel. It was planned (and performed) as follows:
  • Removal of the remaining skeg plating;
  • Preparing the cofferdam underneath the Azipod housing for welding;
  • Preparing the new skeg for installation;
  • Performing a test run of the installation to ensure proper fitup of the weld joint;
  • Installing the skeg;
  • Performing nondestructive examination (NDE) on welds; and
  • Applying corrosion protection.
Meeting Underwater Welding Codes There are two forms of underwater welding: wet and dry. Underwater wet welding is a joining process occurring at ambient pressure with the welder diver in the water without any physical barrier between the water and the welding arc. In underwater dry welding, the repair site is enclosed within a working habitat; the habitat will be dewatered, and welding will be performed under dry conditions. As with any type of welding, above water or underwater, codes and standards must be followed to ensure sound, quality welds. First published in 1983 by AWS, the D3.6M code has become the worldwide industry standard for all welding completed under hyperbaric (elevated pressure) conditions, particularly wet welding of materials. The code specifies three weld classes (A, B, and O) encompassing a range of quality and properties currently produced by application of the various methods. Each weld class defines a set of criteria for weldment properties that must be established during qualification, as well as a set of weld soundness requirements that are to be verified during construction. A weld class specifies a level of serviceability and a set of required properties, as defined by surface appearance, NDE requirements, and mechanical tests, to which welds of a given class must conform. The code defines the classes as follows: Class A welds “are intended to be suitable for applications and design stresses comparable to their conventional surface welding counterparts by virtue of specifying comparable properties and testing requirements.” Class B welds “are intended for less critical applications where lower ductility, moderate porosity, and other limited discontinuities can be tolerated.” Class O underwater welds must meet the requirements of another designated code or standard, as well as additional requirements, to cope with the underwater welding environment. In the spring of 2014, SGS completed a 2.5-year-long joint industry project in partnership with the DNV GL materials and welding department in Hamburg, Germany. The goal of the project was to prove that Class A weld quality, in accordance with AWS D3.6M, could be achieved in wet-welded groove welds. Close to 100 underwater groove weld test plates were welded in test tanks in Miami, Fla.; Long Beach, Calif.; and The Netherlands. Nondestructive examination and mechanical tests were performed by  GL, and all welding data and test results were shared with the classification society throughout the development stage of the joint industry project. Many changes were made to the welding procedure during this time, including joint design, bead placement, and travel speeds. The test results over time showed dramatic improvements in the weld quality with every change to the procedures. In April 2014, groove weld test plates were welded in SGS’s test tank in Miami. Welding of the test plates was witnessed by the American Bureau of Shipping, DNV GL, and Lloyd’s Register. The results exceeded the Class A requirements of AWS D3.6M. In September 2014, SGS was given a certificate from DNV GL that allowed the company to perform permanent repairs by underwater wet welding on certain areas of vessels. Installing and Welding the Skeg After months of preparation, it was finally time to install the skeg. As shown in Fig. 3, the materials for the skeg installation were identified as follows:
  • The cofferdam underneath the Azipod was of a higher tensile steel DH 36, 30 mm thick;
  • The cofferdam bottom plate was also of a higher tensile steel DH 36, 30 mm thick; and
  • The skeg plating was of ordinary hull steel Grade A, 10 mm thick.
The Azipod was prepared during two port stops in Miami. During these stops, underwater welders removed the remaining material from the outer perimeter of the bottom plate of the cofferdam by hydrogouging followed by grinding. The weld joint on the outer perimeter of the cofferdam bottom plate was prepared, and lifting padeyes were installed onto the cofferdam to help with the installation of the new skeg. A new skeg was fabricated by the OEM based on the original design drawings. The process included the installation of lifting padeyes and clips to enable the divers to install and remove scaffolding quickly at the beginning and ending of every work shift. This was done because work could only be conducted underwater during regular port stops. The preparation also included the installation of a backing bar to the new skeg to ensure a complete joint penetration weld could be made between the existing cofferdam underneath the Azipod and the new fabricated skeg. The new, 1200-kg skeg was lowered into the water with a crane — Fig. 5. Once in the water, the load was transferred from the crane to lift bags, and then to lifting lugs welded to the cofferdam underneath the gear housing of the skeg. The new skeg was pulled into position against the cofferdam and aligned using chainfalls and turnbuckles until the backing bar was tight against the bottom of the cofferdam. After the required root opening throughout the weld joint was achieved, strongbacks were welded between the cofferdam and the new skeg. Multiple bead tack welds were welded in several locations, each approximately 50 mm long. Slag was removed from the tack welds and ends were fanned out. Welding was performed in the horizontal (PC) position, employing the wet shielded metal arc welding (SMAW) process — see lead photo. Welds were deposited using the stringer bead technique. During the first port stop, it was required to fill the weld joint to approximately 50% to ensure the skeg would withstand the hydrodynamic forces it would be exposed to. During this time, the turnbuckles stayed in place, the speed of the vessel was limited, and the crew was advised not to perform any erratic maneuvers. Welding was performed with four divers welding simultaneously, two on the inboard side and two on the outboard side of the skeg. The total weld joint length was 6400 mm. With the passes necessary to fill the joint, a total of 128 m of linear weld had to be welded, for which approximately 640 welding rods were  used. Welding was performed with a ∅3.2-mm Hydroweld FS underwater wet welding electrode. Weld time, with four divers welding simultaneously, was approximately 18 h. The Finishing Touches The installation was completed throughout the next few port stops in the Caribbean. Underwater magnetic particle examination was performed on the finished weld and areas of removed underwater weld fixtures. After the welds passed NDE, corrosion protection in the form of underwater, two-component epoxy coating was applied over the welds, the adjacent areas to the welds, and areas where the corrosion protection had to be removed or burned off during welding. This was done to assist in the protection and reduction of metal wastage in those areas due to immersion in salt water by providing a permanent anticorrosive protection. Conclusion Propulsion systems keep ships moving at sea. A broken or damaged propulsion system can render a 100,000-ton ship filled with passengers and goods immobile. With Subsea Global Solutions’s process for repairing skegs with underwater wet welding, vessels can stay the course as repairs are made. Fig. Lead: An underwater welder uses wet shielded metal arc welding to repair the skeg of a cruise ship’s propulsion system.

2024 Platinum Sponsors

2024 Sponsors

Become a Sponsor