Juliana Shipyard in Spain Increases Productivity with Orbital Welding of Chemical Tanker Piping System
Juliana Shipyard in Spain Increases Productivity with Orbital Welding of Chemical Tanker Piping System
Juliana Constructora Gijonesa, S.A., a shipyard in Asturias, Spain, is using advanced technology orbital welding equipment manufactured by Arc Machines, Inc., in the fabrication of a series of chemical tankers. In 1995, JULIANA was awarded the contracts for the building of three chemical tankers (18,950 DWT), in addition to four chemical tankers of more (22,460 DWT) ordered during the next year. All of them are vessels with tanks and pipes in stainless steel, specifically duplex 2205 and 316L. Previous to these contracts, JULIANA had already built five additional chemical tankers for the well-known Norwegian owner KNUTSEN OAS SHIPPING A.S. All vessels presently under contract have been ordered by prestigious international owners, well-known in the worldwide chemical market. These orders reflect the good name that JULIANA Shipyard has earned in the high-technology vessel market.
BOTANY TRIUMPH was delivered to the owner, BOTANY BAY, in March 1997. In
November of 1997, the vessel JO ASK was delivered to the owner JO TANKERS,
followed by the vessel JO EIK in March, 1998.
Photo of the Botany Triumph, a chemical tanker completed by Juliana in March 1997.
Arc Machines Model 15 full-function pipe weld head mounted on a large-diameter stainless steel pipe in preparation for welding a flange to an elbow.
An Arc Machines, Inc. Model 227 Power Supply at the Juliana shipyard was covered with blue plastic for protection from the shop environment. The welding operators have taped the weld schedules to the lid for reference.
A welding operator observes a weld-in-progress using a heads-up display. The HUD permits the operator to make changes in some weld parameters during the weld if needed. The orbital weld head is an Arc Machines, Inc. Model 95-6625 with wire feed welding a copper nickel pipe.
Arc Machines Model 15 pipe weld head mounted on large diameter 316L stainless steel pipe in preparation for welding a flange to an elbow. The Model 95-6625 was also used for this application.
Simultaneously, fabrication has begun on the two first vessels of a series of
four with state-of- the-art automation and diesel-electric engines which have
been ordered by STOLT PARCEL TANKERS. The building of these ships will provide
work for all the shipyard’s workers up until the year 2000. They began the mainframe
of the second tanker in August of 1996 and began working on the piping systems
in September of 1996.
JULIANA’S welding personnel has been decreased from a peak in the 1980s. In an effort to increase their efficiency, JULIANA has been upgrading their welding processes and procedures. At one time they did exclusively stick welding (SMAW), then added MIG/MAG, manual TIG (GTAW), and now orbital TIG. Although Juliana has owned the orbital welding equipment only since the end of 1995, by the summer of 1997 they were welding as much as 90% of their piping orbitally.
which has been in business since 1911, has undergone a series of changes over
the years. For many years they operated as a foundry and boiler forge producing
machinery for mining and the processing of sugar beets. In 1941 they extended
their activities to shipbuilding setting the stage for the modernization and
expansion of the Shipyard beginning in 1956 when they became a wholly owned
subsidiary of the Compañía Euskalduna de Construccion y Reparacion de Buques.
In 1969 several shipyards joined to form ASTILLEROS ESPAÑOLES (AESA) Holding to
which Juliana now belongs.
Juliana’s Technical Department has designed and developed on-site most of the vessels built by the shipyard up to the present time. They make everything for the ship 'from top to bottom'. It is widely known that the improvements and advances in technology at Juliana are due to the desires, efforts, and demands for continued improvements by Mr. Fermin Gutiérrez, Pipes & Modules Workshop Manager. These improvements have resulted in a documented steady increase in productivity.
Piping systems for the vessels are designed and developed by engineers in the Technical Department using CAD-PIPE software and engineering activities are coordinated via computer linkups to other Juliana departments. The ability to design the piping systems on-site gives Juliana’s engineers the flexibility to optimize the piping systems and joint configurations for orbital welding. They aim for a maximum of straight lengths and joint designs suitable for orbital welding. This would be square butt welds for thin-walled tube or pipe with up to 3.5 mm wall thickness, or a slight chamfer on heavier-walled pipe. The change from manual weld end-preparations to an end-preparation suitable for orbital welding was instrumental in saving up to 60% of the welding time from the first chemical tanker which was done mostly by manual welding and the second tanker on which most of the piping was joined by orbital welding. The manual weld prep was an open root which required pre-tacking of small pieces used as spacers to hold the joint in-place for welding. After welding the pieces had to be removed which was time consuming.
Juliana purchased 3 Model 227 microprocessor-controlled power supplies from Arc Machines, Inc.’s European Office (AMI-EO) in Gland, Switzerland. The power supplies provide very accurate control of weld parameters including primary and background pulsed welding current, electrode travel speed, pulse rates, and timing of various levels and functions. The power supply also controls wirefeed speed, torch oscillation and automatic arc voltage control for those weld heads that have these features. Weld parameters for each size of tube or pipe are programmed into the power supply and stored in memory. The weld program, or schedule, may be printed out and used as part of the Weld Procedure Specification (WPS). When operating the Model 227, welding personnel use a heads-up display (HUD) with which they view the weld through a shield and can make changes in weld parameters during the weld should they be required. Cooling units are used with the power supplies to circulate water through the cables, weld heads, and torches to keep them at normal operating temperatures.
In addition to the orbital welding power supplies, Juliana also purchased 3 types of orbital weld heads. These included a Model 15 full-function pipe welding head with the capability of feeding wire into the weld. It can also oscillate the torch back and forth across the weld seam to produce a weave bead, and has automatic arc voltage control used to maintain a constant arc gap. The Model 95 series of weld heads have the capability of feeding wire with an external wire feeder, and a mechanical arc gap controller to prevent the tungsten electrode from hitting the weld puddle if the pipe is out-of-round. In addition, two Model 9 fusion weld heads, used to make autogenous welds on tube or thin-walled pipe, were purchased to weld the small diameter stainless steel sleeve welds. In an operator training class given by AMI-EO, six men were trained to use all three types of weld heads.
Copper-nickel pipe (90/10) in sizes from one inch to 10 inches OD was used for steam lines and the sea water lines used in the ship’s cooling water system. Copper-nickel is used in this application because of its superior corrosion resistance in the marine environment. Sizes below one inch OD were done manually because filler wire for orbital welding was not available at the time these welds had to be done. The filler used for orbital welding was 0.8 mm wire. All of the orbital welds on copper nickel were done in a single pass, even with the larger diameters and wall thicknesses up to 3.5 mm.
Copper nickel is very difficult to weld by hand, and manual welders with the skill to weld this material are a scarce commodity but when the Botany Triumph was being built, orbital welding was not available, so the copper nickel pipe on that ship was welded by hand. The orbital welding for the second ship was done with a single level program with 140A of primary weld current and 110A of background current. Copper nickel is very different to weld than stainless steel in that it takes a long time to get full penetration of the wall initially, but then the weld head must travel at maximum speed to avoid overpenetration. A gas mixture of 95% argon/5% hydrogen was used as the shielding gas for the copper nickel as this combination produces a hotter arc with deeper penetration at the same current setting than pure argon.
As of April ‘97, Juliana was at the halfway point of completing the copper-nickel welds for the second ship which was on-schedule for the job. The orbital welding process is less repeatable with copper nickel than with stainless and the welding operator must generally make some adjustments during the weld. However, the end result with orbital welding is very good. The ID weld bead was flat, which was acceptable, or slightly convex which was preferred. Another benefit of using the orbital equipment was that it was cleaner to operate and resulted in a cleaner working environment for the welders.
End-Preparations for Orbital Pipe Welding
|The weld joint preparation for the Model 15 and Model 95 weld heads for 316L SS with wall thicknesses of 1 to 3.2 mm and diameters greater than 24 mm was a square butt joint.|
|The weld joint preparation for the Model 15 and Model 95 weld heads for 316L SS with wall thicknesses greater than 3.2 mm and diameters greater than 24 mm had a land of 1.5 mm and a slight chamfer of 30°.|
Stainless Steel was used for product lines on the ship. The list of products that a chemical tanker might be expected to transport runs 13 pages in length so cannot be listed here, but run the gamut from various types of acids and alcohol, to oils, including cooking oils, and noxious liquids. Welds on product lines all had to be fully penetrated. The Model 15 weld head was used to weld flanges onto pipe and fittings of 316L stainless steel. The Model 15 mounts on the pipe via a guide ring, and the 10 inch guide ring could be used to weld the smaller 4 and 5 inch flanges as well. The Model 95-6625 weld head was also used to weld flanges to pipe. While the welding engineers preferred the precision of the Model 15, the operators preferred using the Model 95, since it requires less set up time as it mounts almost instantly on the pipe.
gas is used to purge the ID of the pipes during welding to prevent oxidation.
Oxidation results in discoloration of the weld and heat affected zone and is
sometimes referred to as heat tint. The amount and intensity of colour of the
heat tint is strongly correlated with loss of corrosion resistance in both
manual and orbital welds, but argon gas is expensive and large diameter pipe
requires a huge volume of argon for a proper purge. In this application,
Juliana used a purge mandrel tool (PMT) with the Model 95-6625 and Model
95-2375 weld heads. The PMT holds the fitting in place without the need to
pretack, and limits the volume of pipe ID that requires purging to the area
directly surrounding the weld bead and HAZ. This saves both the time required
to fill the pipe with argon and greatly reduces the cost of purge gas.
The Model 9AF-900 fusion weld heads were used for welds of 10-18 mm diameter 316L stainless steel tube with a heavy sleeve as shown in the chart below. The welds connect a tube to a valve on the ship used to control the flow of products. For the first ship Juliana did 5,000 small sleeve welds orbitally out of a total of 8,000 welds. Access to weld locations on the ship was very difficult when the welds were done manually. For the second ship, 5,000 orbital welds were done in the workshop, and 3,000 were done on board ship to weld the tube to the valve. The welders were able to do 125-130 orbital sleeve welds per day using two heads. Of the 8,000 orbital welds there were only 2 failures which occurred when these welds failed the hydraulic test. This represents a reject rate of only 0.025% which is excellent.
Weld joint preparation for small diameter tube welds which were done with the Model 9 fusion weld head. A sleeve was placed over the square butt joint and both ends of the sleeve were orbitally welded. The weld bead penetrated to the tube ID. Tube sizes were as indicated in the above chart.
The list of rules and regulations to which builders of chemical tankers must comply is extensive. It includes classification of the vessel by Lloyd’s Register of Shipping, as well rules and regulations by more than a dozen other regulatory agencies. Weld Procedure Specifications (WPS) were done for the various sizes of stainless steel pipe and for the small diameter sleeve welds. This specified the preparation of test coupons which were subjected to bend and tensile testing to verify that the mechanical properties of the weldments met the minimum tensile strength and ductility specified for the base metal. Vickers hardness tests were done, macro and micrographs were done of the welds to check the composition of the weld and HAZ as well as to verify the absence of cracks. Chemical analysis by atomic emission spectrometry was done to assure that the base metal conformed to specification. Corrosion testing was done to evaluate the susceptibility of the weldments to intergranular and pitting corrosion. The sleeve welds were hydrotested at three different pressures which were 6 kg/cm2; 25 kg/cm2; or 170 kg/cm2 depending on the product, with lines for the more hazardous chemicals subject to the greater pressures. Testing of the qualification welds was done by the Instituto Technologico de Materiales in the presence of an Inspector for the society of Lloyd’s Register to meet the qualifications of Lloyd’s Register of Shipping.
View of chemical tanker under construction. Some piping systems are visible. The firewater system is painted red. The crane is used to lift prefabricated piping assemblies aboard ship.
Visual inspection of a minimum of 5% of the IDs of the production welds is required by law. Juliana has always inspected 50-60% of their manual welds but Lloyd’s of London has permitted them to reduce this to the 5% level for the orbital welds. When viewing the radiographs of the orbital welds, Lloyd’s inspector became visibly upset since all of the X-rays of the welds appeared to be identical and he thought they were all taken from the same weld. The orbital welds were so consistent that the inspector had to be convinced that the X-rays were indeed from different welds. The quality of the orbital welds was such that Juliana was able to drastically cut back on their weld inspection requirements.
Orbital welding provides a very significant improvement in productivity compared to manual welding. The welding operators were able to make 14-18 welds per day per machine on the stainless steel pipe compared to only 4 or 5 per day with manual welding. Fewer welds were possible on the copper nickel since that material was more difficult to weld, but there was still a significant advantage to orbital welding. Orbital welding has greatly improved the efficiency of Juliana’s operation. For example, when they were doing all the welding manually, they had to run two shifts a day to stay on schedule. Since the change to orbital welding they have been able to operate with only one shift a day beginning at 7:00 AM and ending at 2:45 PM. In addition, orbital welding has significantly reduced the amount of weld inspection required which is a saving of both time and money.
Juliana plans to continue to weld the carbon steel piping manually, as this material is generally less suitable for orbital welding, but they intend to weld their duplex stainless steel piping using the orbital equipment once they have completed their qualification welds on this material. The mechanical properties and corrosion resistance of duplex can be degraded by welding unless the heat input is well controlled and proper purging procedures are in effect. Orbital welding is particularly advantageous for duplex material because it allows the development and testing of weld procedures which, once done successfully, can be repeated from weld-to-weld indefinitely.
Orbital welding has proven to be very effective for a variety of applications in shipbuilding. Significant improvements in weld quality, productivity and practicality were evident, leading to lower costs and more efficient operations.
Published in the March, 1999
issue of Stainless Steel World
By Barbara K. Henon, Ph.D., Arc Machines, Inc.
The author gratefully acknowledges the kind assistance of Mr. Fermin Gutierrez and Julio Martin of JULIANA SHIPYARD for sharing their expertise in shipbuilding and field experiences with orbital welding.