Results of confined head
The confined head was applied to the following three specific tube welding qualification procedures :
a) Butt welding of pipes
Process trials have been performed using AISI304L, IN600 and FE35 pipes, with wall thickness of 1 mm and diameter of 25 mm. After many trials, the parameters were determined for all the materials.
b) Transparency welding of sleeves
The same pipes used in butt welding set-up were used also in this case. Sleeves, inserted into pipes, were welded from inside.
Altogether the confined head and the processes parameters were qualified by welding a stainless steel sleeve (0.75 mm thickness, i.d. 21.5 mm) from inside into a pipe of the same material with inner diameter equal to the outer diameter of the sleeve, achieving a penetration depth of around 2.5 mm with a mean power of around 600W on the workpiece
c) Cutting of pipes
Trials have been performed to confirm the viability of pipe cutting using the confined head, using pipes of the same three materials as before.
Development of a focussing head for hostile environment.
The laser processing head is suitable to work at a remote site in underwater environment at pressures of up to 10 bars. The maximal laser power for cutting and welding is up to 2 kW. The head is equipped with a shielding nozzle for under water processing, a wire feeding device and specific on line monitoring sensors to allow a remote operation and control, which in particular are: vision system (CCD-camera) with illumination and adjustable focusing to enable a remote alignment of the working head relatively to the workpiece, laser power sensor, distance sensor and plasma sensor.
Welding under hyperbaric conditions/Comparison to ambient pressure
The results showed that the useable pressure range can be extended when a higher power density is applied. Therefore one requirement for laser sources used for under water welding is a good beam quality which allows to use thinner fibers.
Construction of the underwater nozzle with labyrinth sealing
By activating the gas supply an equilibrium is initially achieved between the internal pressure in the inner part of the nozzle and the surrounding water. The pressure in the inner part of the nozzle is then adjusted to provide an approximately 0,5-0,8bar pressure difference of to the outside environment which results in a water free volume between the front plate and the workpiece surrounded by the labyrinth sealing
In order to demonstrate the feasibility of a patch welding repair two 4mm thick metal sheets were positioned at 7,5mm between nozzle and workpiece. The groove formed by the two sheets constituted a sort of channel through which the working gas flowed from the central region of the nozzle. To compensate for this outflow an increase of approximately 0,2 to 0,3bar was required in the pressure difference of the working gas.
Final validation
The goal of this validation phase was to apply the parameters of the development task to the real in-situ system. In that case of under water laser processing the operation was definitely in remote configuration. Using the real time feed back of power sensor, distance sensors, video camera, plasma sensor, wire speed value and the axis position and speed of the head, the is now able to run any kind of process (cutting, welding with or without wire feeder) on most of geometrical work pieces configuration in serial preprogrammed processing mode
Covered processes :
As planned most of processes have been validated in industrial application especially the hostile environement ones. Main of under water welding validation was performed on patch welding on pipe base material. The material used was 304 L and 316 L in to differents thicknesses, 1.5 and 3 mm.
One week after unloading the components, the system was turned on to perform the first industrial dry weld with filler wire.
During this overall first validation period all the system capabilities were tested
The next step was to validate the system and processes under wet conditions. To reach this goal using the first period configuration, the carrier and head system and sub-systems have been immerged into a custom sized stainless steel pool. This task was the last point to validate regarding the viability of the previous 10 tasks of the programm, before the under water sessions.
It is proposed to develop a mobile high power YAG laser processing system for in-situ maintenance of industrial plant in hostile and confined environments. Present CO2 laser process systems do not allow for the accessing of work at a distance from the power source, in a confined remote space, or in a hostile environment, such as, for example, in explosive gaseous mixtures, at over ambient pressures or underwater. The proposed system is based on a high power YAG laser source, and specially designed torches that can be both deployed at distance from the source, and can cater for the hostile environment, to undertake high quality cutting welding and related operations. This system will be realised through the completion of the following tasks :
(i) Modification of the laser system
(ii) Development of small diameter
(iii) Development of nozzles
(iv) On-line monitoring
(v) Cutting, welding
(vi) Quality control
(vii) Final validation
The successful completion of the Project should produce substantial gains in plant availability in a number of industrial sectors including the power generation, shipping and petro chemical industries.
