Hyperbaric welding

 

Hyperbaric welding is the process of welding at elevated pressures,normally underwater.Hyperbaric welding can either take place wet in the water itself or dry inside a specially constructed positive pressure enclouser and hence a dry environment. It is predominantly referred to as hyperbaric welding when used in a dry environment, and underwater welding when in a wet environment. The applications of hyperbaric welding are diverse it is often used to repair ships, offshore oil platforms, and pipelines. Steel is the most common material welded.
Dry welding is used in preference to wet underwater welding when high quality welds are required because of the increased control over conditions which can be exerted, such as through application of prior and post weld heat treatments. This improved environmental control leads directly to improved process performance and a generally much higher quality weld than a comparative wet weld. Thus, when a very high quality weld is required, dry hyperbaric welding is normally utilized. Research into using dry hyperbaric welding at depths of up to 1,000 meters (3,300 ft) is ongoing. In general, assuring the integrity of underwater welds can be difficult (but is possible using various nondestructive testing  applications), especially for wet underwater welds, because defects are difficult to detect if the defects are beneath the surface of the weld.
Underwater hyperbaric welding was invented by the Russian metallurgist Konstantin Khorenov in 1932.

Application

Welding processes have become increasingly important in almost all manufacturing industries and for structural application. Although a large number of techniques are available for welding in atmosphere, many of these techniques cannot be applied in offshore and marine application where presence of water is of major concern. In this regard, it is relevant to note that a great majority of offshore repairing and surfacing work is carried out at a relatively shallow depth, in the region intermittently covered by the water known as the splash zone. Though numerically, most ship repair and welding jobs are carried out at a shallow depth, the most technologically challenging task is repair at greater depths, especially in pipelines and repair of accidental failure. The advantages of underwater welding are largely of an economic nature, because underwater-welding for marine maintenance and repair jobs bypasses the need to pull the structure out of the sea and saves valuable time and dry docking costs. It is also an important technique for emergency repairs which allow the damaged structure to be safely transported to dry facilities for permanent repair or scrapping. Underwater welding is applied in both inland and offshore environments, though seasonal weather inhibits offshore underwater welding during winter. In either location, surface supplied air is the most common diving method for underwater welders

Dry welding

Dry hyperbaric welding involves the weld being performed at raised pressure  in a chamber filled with a gas mixture sealed around the structure being welded.
Most arc welding processes such as Shielded Metal Arc Welding (SMAW), Flux-cored arc welding(FCAW), Gas tungsten arc welding (GTAW), Gas metal arc welding (GMAW), Plasma Arc Welding (PAW) could be operated at hyperbaric pressures, but all suffer as the pressure increases. Gas tungsten arc welding is most commonly used. The degradation is associated with physical changes of the arc behaviour as the gas flow regime around the arc changes and the arc roots contract and become more mobile. Of note is a dramatic increase in arc voltage which is associated with the increase in pressure. Overall a degradation in capability and efficiency results as the pressure increases.
Special control techniques have been applied which have allowed welding down to 2,500 m (8,200 ft) simulated water depth in the laboratory, but dry hyperbaric welding has thus far been limited operationally to less than 400 m (1,300 ft) water depth by the physiological capability of divers to operate the welding equipment at high pressures and practical considerations concerning construction of an automated pressure / welding chamber at depth.

Wet Welding

Wet underwater welding directly exposes the diver and electrode to the water and surrounding elements. Divers usually use around 300–400 amps of direct current to power their electrode, and they weld using varied forms of arc welding This practice commonly uses a variation of shielded metal arc welding, employing a waterproof  electrode Other processes that are used include flux-cored arc welding and friction welding  In each of these cases, the welding power supply  is connected to the welding equipment through cables and hoses. The process is generally limited to low carbon equivalent steels especially at greater depths, because of hydrogen-caused cracking
Wet welding with a stick electrode is done with similar equipment to that used for dry welding, but the electrode holders are designed for water cooling and are more heavily insulated. They will overheat if used out of the water. A constant current welding machine is used for manual metal arc welding. Direct current is used, and a heavy duty isolation switch is installed in the welding cable at the surface control position, so that the welding current can be disconnected when not in use. The welder instructs the surface operator to make and break the contact as required during the procedure. The contacts should only be closed during actual welding, and opened at other times, particularly when changing electrodes.
The electric arc heats the work piece and the welding rod, and the molten metal is transferred through the gas bubble around the arc. The gas bubble is partly formed from decomposition of the flux coating on the electrode but it is usually contaminated to some extent by steam. Current flow induces transfer of metal droplets from the electrode to the work piece and enables positional welding by a skilled operator. Slag deposition on the weld surface helps to slow the rate of cooling, but rapid cooling is one of the biggest problems in producing a quality weld

Hazards and risks

The hazards of underwater welding include the risk of electric shock to the welder. To prevent this, the welding equipment must be adaptable to a marine environment, properly insulated and the welding current must be controlled. Commercial divers must also consider the occupational safety issues that divers face; most notably, the risk of decompression sickness due to the increased pressure of breathing gases  Many divers have reported a metallic taste that is related to the galvanic breakdown of dental amalgam  There may also be long term cognitive and possibly musculo skeletal effects associated with underwater welding.

 

 

 

 

ROBOTIC APPLICATION IN NDT

The Use of Industrial Robots for NDT Applications 

Nondestructive testing is the preferred quality control technique for many manufacturers from different domains ranging from industrial to aerospace. With automated NDT, we use scanners and robots to increase the speed and repeatability factor of NDT techniques,creating

much more efficiently produced precision measurements. However, obvious automated NDT scanner requirements are needed to achieve high quality control and precision measurements.

This article provides a basic comparison between typical Cartesian scanners using a combination of linear axes (X, Y and Z axes) and rotational axes, and articulated robotic arm systems using six polar axes, often used for handling machine tools, welding and part movement. 

 AUTOMATED CARTESIAN SCANNERS

Typical scanners in the NDT industry consist of Cartesian scanners that can be customized for their respective job specifications. These systems are usually designed with highly accurate actuators, servo or stepper motors and optical encoder modules, making them ideal tools for real-time signal acquisition during the axes movement. They also provide automation with increased inspection speed, real-time signal processing, imaging capabilities and scanning repeatability. However, in order to achieve such design characteristics, stringent requirements must be imposed on the scanner’s automation technology being used. Some of these requirements consist of: the mechanical design for high positioning accuracy of all axes; the motion control strategy designed for fast position feedback; the required real-time encoder monitoring; the integration of high-speed interface for fast data transfer rate. 

Whether using scanners for automated ultrasonic or eddy current testing, the quality of the scanner is related to the final results of C-scan mapping, which are directly related to the signal acquisition and probe’s position and stability during said acquisition. This becomes even more critical when dealing with parts exhibiting complex 3D geometries. An additional challenge exists in designing automated scanners with increased dexterity for handling common complex geometries. The Cartesian scanner solution then becomes a multi-axis scanner where the position of all axes needs to be synchronized to achieve accurate testing. Although the ultimate aim of automated NDT is to achieve speed and carry out total inspection, when performing scanning of critical components such as for the aerospace industry, inspection reliability, resolution and repeatability become more important than the overall inspection time.

The reliable positional accuracy and repeatability performances of such scanners are usually obtained from good metrological alignment conditions. Once these scanners are designed with enough axes, they can reach any inspection point in 3D space and follow the inspected part curvature. In addition, when using an advanced motion control system, Cartesian scanners can be extremely precise and capable of accurately and reliability scanning complex surfaces with relatively high speeds.

ARTICULATED ARM ROBOTS

Industrial robotic arms present precise articulated mechanical links whose functions are similar to a human arm. Their links are jointed to provide rotational motions and manipulate objects within a certain volume. Off the shelf industrial robots are recognized as a polyvalent and robust solution for many applications: welding, palletizing, material handling, machine tending, laser cutting, machining, etc.
Compared to typical Cartesian gantry systems, the concept of an articulated arm provides a system with greater dexterity. Such robots can help advanced NDT methods if they meet the basic standards of automated NDT testing: data acquisition, repeatability, accuracy and precision.

MOTION CONTROL
The important complication of using robotic arms for automated NDT is the proprietary motion controller design that these robot use. With such control, we are locked into proprietary programs and limited motion control capabilities.
More specifically, we have limited control and not enough information of the robot positions when it moves from one point to another. Automated NDT systems require acquiring data on the fly while the robotic arm is moving. Therefore, the motion control system needs to handle extremely fast control changes (fast PID controller loops). For example, in applications that require the robot to move fast and perform contour following motions around a complex surface, smooth and precise trajectories must be maintained during the robot movement. When the PID loops close at a slow pace, the robot will not move on required precise trajectories. This can results in a jumpy motion of the robot and losses of the NDT signal measurements. Current industrial robots offer slow PID control loops, estimated around 10 times less than the required speed to perform fast and accurate NDT scanning of complex parts.

 DATA ACQUISITION

Another challenging factor for using industrial robots for NDT application is the required data acquisition speed. Capturing NDT data in real time while using a robotic arm is a challenging feat since it requires real-time robot position monitoring. This means that a direct encoder feedback has to be made available on the robot, which is generally not the case. All standard robot controllers will provide low rate of position feedback at around 200 Hz, after being processed by the motion controller unit. As the robots “true” position must be attached to each measurement point and no interpolation is allowed, the rate at which position feedback refreshes itself has a proportional impact on the inspection speed.

By working on the main challenges identified above, industrial robots can eventually replace the conventional Cartesian scanners in selected NDT application if motion control functions and encoder feedback monitoring are customized. But at this moment without such modifications in terms of the support data transfer, link and communication protocols, an efficient use of articulated robotic arms for NDT is still a work in progress

HYPER LOOP

Ben Lippolis flew across the country to take part in a student hyperloop competition hosted by Elon Musk. This was no science fair. At the Space Exploration Technologies Corp. headquarters on the outskirts of Los Angeles, engineers from some of the world’s top universities loaded 2,000-pound hunks of metal onto a tubular track and, one by one, raced their pods to see who could clock the fastest speed.
Lippolis, a recent graduate of Northeastern University, teamed up with some classmates and students from Canada’s Memorial University of Newfoundland to form team Paradigm. They’ve been toiling away to construct a passenger train that can travel at high speeds inside an enclosed tube, as envisioned by Musk. To fund their project, including air travel, accommodations, parts, machinery and transport for the pod, they cobbled together grants from the Canadian government and corporate donors.
In the two years since Musk’s SpaceX started organizing these competitions, the rocket company has found a unique formula for luring talent at little cost. While most companies spend extensively on recruiting, the hyperloop competitions consistently bring in eager, young prospects on their own dime jockeying to show off their abilities. Winners of last month’s contest received no prizes, and all entrants were required to hand over rights for SpaceX to use any of their technology in the future without compensation.

 The real reward: a shot at impressing their hero. “Everyone on our team really looks up to Musk and what he’s been able to do for the world so far,” said Lippolis, 23. “The thought that something you’ve directly worked on and helped develop could one day be incorporated into a system that would vastly improve everyone’s quality of life is truly amazing.”
Hackathons and other technical competitions have been criticized for demanding that participants surrender the right to collect licensing fees from the organizer if that company happens to make use of their creation in the future. But the lack of any award money at SpaceX’s event is particularly unusual. Even so, several contestants said they were happy to participate and offer their work as “open-source” for anyone to use, gratis. Tim Houter, who started a hyperloop company in the Netherlands called Hardt Global Mobility after winning a past SpaceX competition, said his team’s early work was rudimentary and that they’ve come a long way since then. “There are no issues regarding the intellectual property.”
A SpaceX spokeswoman said the company asks for rights to use participants’ technology as a tradeoff for access to the test facilities. She declined to disclose the cost of building the track, which is almost a mile long and simulates near-vacuum conditions. The technology licenses are needed to protect SpaceX from potential litigation in the future, she said. The student teams retain ownership of the technology.

Musk is making plans to build his own underground hyperloop from New York to Washington, D.C., Bloomberg reported last month. The student events provide his companies with valuable insights, said Christian Claudel, an assistant professor at the University of Texas at Austin and adviser to his school’s hyperloop team. “They get to build that facility that they will use anyway, and they let a few teams test their equipment,” he said. “It’s a very good deal for SpaceX.”
Many students said their main hope was to secure a job someday on Musk’s team. The billionaire’s companies recognize the recruiting opportunity. Representatives for SpaceX and Tesla Inc. prowled the staging grounds, where booths ranged from simple tables covered in résumés to an elaborate setup of hammocks and Weber grills, courtesy of Sacramento State. Recruiters made small talk and collected contact details from some contenders. Students also got face time with SpaceX engineers, who helped them prepare for various technical tests before the weekend race.

The effort paid off for the champions of last year’s competition. One member of that team, from the Massachusetts Institute of Technology (MIT), now works as a structures engineer at SpaceX. Another is a robotics engineer at NASA’s Jet Propulsion Lab. Others went to Hyperloop One, a venture-backed company inspired by Musk’s vision and a sponsor of SpaceX’s 2016 event. (The start-up is now holding a competition of its own to identify commercially viable routes and revealed finalists on Thursday.)
MIT didn’t participate last month, in part because so many team members had graduated and gotten jobs, said Douglas Hart, a faculty adviser and professor of mechanical engineering. The events were probably as beneficial to Musk as they were to the students because it showed his engineers what works and what doesn’t with magnetics, brakes and other materials at high speeds, Hart said. “SpaceX was learning at the same time everyone else was.”
Lippolis and his Canadian teammates didn’t win this time, but they plan to do it all over again next summer at SpaceX’s 2018 event, which is taking applications until the end of next week. The Paradigm team hopes to show that its air-bearing levitation technique can reach 200 miles per hour, matching the speed of the winning team’s wheel-based train at the last competition.