Viking Vessel Services presents an innovative process, called Tuff Tube Transition, or TTT (US Patented and International Patent Pending). TTT is a Lap joint / sleeve type connection for tube-to-tube & tube-to-header repairs, and new ASME Section I header assemblies and stubbed headers. TTT eliminates costly open butt welds and the need for a back-purged system during welding.

High Alloy Tubes repairs, using a grade such as T91, require purging when the system cannot be blocked, and are conventionally dammed on each side of the butt weld. A football needle or gas lens is placed up to the open gap in the butt weld, and with a conventional repair, this is the only line of defense for shielding. If oxidation occurs due to a lack of backing gas, this discontinuity can render a crack in the root, and will ultimately cause service failure. TTT does not require ANY back-purging on ANY alloy, for both repairs and new header assemblies.

TTT eliminates the need for Non-Destructive Testing, such as RT (or Radiographic Testing). On a recent job with over 150 tube-to-tube tie-ins, utilizing T91 grade tube materials in the HP (or High Pressure) Section of the HRSG, an RT examination performed both before and after Post Weld Heat Treatment, would have required over 300 RT shots for soundness in a conventional repair. TTT drastically reduces the cost for this activity and also the downtime for safety precautions involved with the use of Radiographic Testing. In conjunction with the time saved by eliminating RT , in this particular case study, production time was reduced from 2 weeks to just over 2 and half shifts, and with an average weld fit up time of 20 - 25 minutes per tube-to-tube tie-in.

TTT self- fit-up and alignment, allows for a faster and more reliable joint alignment. With T91 tube material for example, conventional butt welds require time-consuming fit-up alignment equipment, as T91 material needs to be at a 400 to 450 degrees Fahrenheit pre-heat temperature prior to any thermal activities, such as tacking and welding. With TTT being a secure fit-up, a simple clamp can be placed, which does not interrupt the thermal pads providing pre-heat, which are wrapped around the component. This gives the user the added advantage of not having to also hand lay out bevels or utilize mill-hogs for fit-up.

Research points to the vast majority of tube failures being in the Heat Affected Zone of the weld toe in the tube-to-header connection. The thermal expansion difference between tube and header is causing the tube to literally pull away from the header, or induce a fatigue crack, causing the service failure in the tube connection. Based on FEA Analysis performed on both conventional and TTT lines, TTT demonstrates a far stronger, and more durable connection. Due to the design of TTT line of products, TTT has a 50-75% increase in service life and cycle fatigue durability, compared to conventional connections.

In a nutshell, TTT provides a far better connection, is significantly easier to install during a repair situation, and enormously increases the life expectancy before another repair is required. There is a minimum of 50% cost savings over conventional repairs by utilizing TTT for repairs or new header assemblies.