The heavy industries of Europe are interested in laser welding as soon as the technology is mature for very thick plates.
By Kent Krøyer
“We are very interested in the development of laser welding. We might use it for joining together heavy steel plates side by side for the large substructures we are manufacturing. We are constantly on the lookout for easier, more versatile methods than the traditional submerged arc welding technology,” says Morten Mørk, Department Manager at Bladt Industries in Aalborg, Denmark.
Bladt Industries has a long history of manufacturing large steel constructions for the oil and gas industry, as well as steel bridges and substructures for large wind turbines. This involves welding of sizeable and 45-110mm thick plates. Structures which are currently created by submerged arc welding (SAW ).
“We are not currently performing tests with laser welding, but we recognize that at some time this technology will become interesting,” he says.
A stockpile of transition pieces for the London Array wind farm. Photo: Bladt Industries
SIF open and awaiting
Another player in the field of very heavy steel production is SIF Group from the south of the Netherlands.
SIF Group is a company with extensive experience in bending, rolling and welding thick steel plates into tubes for oil platform structures and wind turbine towers. Here too, the preferred choice of welding technology is the traditional submerged arc welding.
A typical butt-welding of two 40 mm plates at SIF requires about 18 welding passes with SAW technology.
“We are indeed interested in laser welding when it becomes available for the steel plate thickness that we use, e.g. 40- 120 mm,” says welding engineer William Lafleur, pointing out the advantages of less distortion because of the fast welding runs, the ability to penetrate the entire plate thickness in a single run, the reduced use of filler material and the reduced need for post-weld milling.
However, he is concerned that the high demands of the plate preparation before the laser welding may be a barrier to the introduction of lasers. Also he believes that when the plates get really heavy, such as 80-90 mm, the laser penetration may not be sufficient without a vacuum, which would require a costly vacuum chamber.
It has been said by critics that introducing laser welding would require the building of completely new factories, due to large changes in production planning. This is not a concern for William Lafleur.
“I think it must be possible to add a laser welding station to an existing factory. Perhaps all weldings could not be replaced at once; it is likely that some would be easier than others.”
He points out, however, that the certifying authorities may be a bit conservative regarding new welding technologies. This could be a delaying barrier for laser welding.
SAW is a strong technology
Another barrier for the introduction of laser welding is the fact that traditional submerged arc welding (SAW) can be taken to quite an advanced level in serial production. One example is at Europipe GmbH in Mühlheim an der Ruhr, Germany.
Submerged arc welding at Europipe is developed to an advanced level. A plate thickness of 29.6 – 40.1 mm can be welded at speeds up to 2.5 meter/minute. Photo: Europipe
Europipe’s most important products are the longitudinal welded oil and gas pipes that run across the continents, supplying nations with energy. A current project is the 889 kilometer long Australian Ichthys subsea pipeline for liquefied natural gas. The pipes to be used will have a diameter of 1067 mm and a wall thickness of 29.6 to 40.1 mm.
“We did conduct a hybrid laser-arc welding test some years ago, but it was not very successful. It was not able to compete with submerged arc welding at that time. The laser welding speed was too slow and the quality was not better than gas metal arc welding. We have welding velocities of up to 2.5 meter per minute,” says Dr. Christoph Kalwa from the R&D department of Europipe.
He points out that the submerged arc process has been adapted and automatized for very efficient production at Europipe. A thick-walled gas pipe of up to about 45 mm is typically welded in just two runs – one on the inside with four wires and one on the outside with five wires.
Microwave-testing of submerged arc welded pipes at Europipe. Photo: Europipe
Tests rejected laser
During Europipe’s tests of the laser welding technology it was shown that continuous tack welding, meaning temporary fixation of the workpieces, could be done with results comparable to those of continuous gas metal arc welding, GMAW (continuous consumable electrode and shielding gas, ed.), but the environment was too dusty for proper laser welding.
As a result of Europipe’s trials, it was found that there was no benefit using laser welding technologies compared to the traditional SAW , and questions about weld properties, such as fusion line toughness, have still to be solved.
The production of Europipe’s large gas pipes involves longitudinal welding which will be stressed hard when the gas flows (onshore typically up to 100 bar, offshore up to 250 bar). This calls for a very high welding quality.
However, laser welding is known for very high quality, once the proper welding parameters are set. And laser welding is still being considered in the pipeline business.
“I know that many people are thinking of automatized laser-arc welding for girth-welding of pipelines,” says Christoph Kalwa.