Noble Drilling retained Applied Ultrasonics to employ Ultrasonic Impact Technology on the structure of one of their ABS classified semi-submersible offshore drilling rigs, the Ton van Langeveld, which was deployed in the North Sea. The rig, built in 1979, had consumed a considerable portion of its fatigue life from the years of high demand work in the face of some of the worst operating conditions in the world. In the North Sea, offshore drilling rigs take a constant beating and welds are exposed to enormous stress coupled with the corrosive saltwater environment.
COST OF OFFSHORE ASSET MAINTENANCE
In the oil and gas industry lost production and equipment maintenance create ongoing high costs, but some of these costs are avoidable. Steel fatigue and corrosion are two of the primary causes of downtime and maintenance on offshore drilling rigs. The metals that makes up rigs, platforms, structures, cranes and tools are at constant risk of stress, corrosion and cracking damage. Prior to UIT there was no effective proactive method for weld life extension and increasing steel strength. Millions have been spent every year to combat this deterioration of offshore assets.
Applied Ultrasonics' UIT is a proven, portable, and easy to use process that extends fatigue life by up to 10 times and increases fatigue strength by as much as 70%.
Applied Ultrasonics personnel treated the S355-J2G3 steel welds both inside and outside of the cross bracing (the middle columns, K-joints, trumpets, and outer columns/chain lockers) using UIT. Work was performed with minimal time on the site, ensuring uninterrupted workflow while the Ton van Langeveld was in dry-dock. Applied Ultrasonics portable equipment was used to treat welds that were deep inside enclosed areas, thus imparting compressive stresses and stress relief in areas that are inaccessible to other methods. Noble Drilling engineers estimate that UIT will extend the fatigue life by a factor of 6 to 8 times.
CERTIFICATIONS
Applied Ultrasonics UIT technology is certified by numerous 3rd party organizations related to the Oil and Gas industry. These certifications include the following:
American Bureau of Shipping
Det Norske Veritas
Lloyds of London
The following renowned facilities have published independent research of the UIT process:
Lehigh University
University of Texas at Austin
Portland State University
Sheffield-Hallam University
Stuttgart University
UIT BENEFITS
For general applications in the Oil and Gas Industry, UIT is able to enhance new or refurbish old materials. UIT delivers:
• Compressive residual stresses
• Stress relief
• Grain modification
• Increased surface hardness
If used as a weld treatment, UIT also modifies the weld toe geometry.
UIT imparts compressive residual stresses to a depth of more than 0.010" or 2.5 mm, due to ultrasonic acoustic coupling.
There are three different zones that experience UIT effects and they are shown in figure 1. These effects result in fatigue life
enhancement and suppression of stress corrosion cracking.
Residual stresses and geometric stress concentrations are the two largest factors affecting fatigue life. The modification of the grain
structure and weld toe geometry are shown in figure 2.
We are confident that the benefits of Ultrasonic Impact Technology will result in significant improvements for the oil and gas industry. UIT has been repeatedly proven to increase fatigue life, fatigue strength and corrosion resistance. Applied Ultrasonics can provide service onsite to maximize cost effectiveness for the customer.