TPT July 2019

T E CHNOLOG Y

Submerged arc welding systems used to fabricate high-pressure spools

and nickel alloys (Monel, Inconel and Hastelloy), copper and copper alloys and titanium. This extensive capability, and the fact that some materials are fabricated whereas others are clad or weld-overlaid, calls for a broad range of welding processes and consumables. FAI Officine Di Carvico has been using ESAB welding equipment and consumables since the early 1970s. One example of the type of system that plays a crucial role in the company’s production is the ESAB Aristo 1000, six of which are used by FAI for submerged arc welding (SAW). ESAB’s Aristo 1000 AC/DC SAW power source benefits from a number of features that help FAI to maximise productivity without compromising quality. For example, Bead Profile Modelling™ provides adjustable AC settings for precise control of penetration profile and depth, dilution, arc stability and weld appearance for the optimum productivity and quality of each weld. In addition, the machine can switch between AC and DC ‘on the fly’ to eliminate the stop/start routine that is normally required and which can result in downtime and weld defects. CableBoost™ is a patent-pending technology that ensures the performance of the power source is unaffected, even when long welding cables are used. For applications requiring higher welding currents, two Aristo 1000 AC/DC units can be connected in synchronised parallel mode. FAI uses the ESABAristo 1000 power sources in conjunction with column-and-boom manipulators, normally with roller beds or positioners, for fabricating high-pressure spools from F22 modified alloy steel. For these spools, which are destined for use in hydrocarbon flow lines, the diameters range from 50mm to 1m (2" to 40") and the wall thickness from 20 to 100mm. Typically the welding wire diameter is 2.5mm and the heat input is maintained at a low level specified by FAI, namely 0.76 to 1.54 kJ/mm for diameters of 6" to 8", and 0.86 to 1.35 kJ/ mm for 14" and greater. With a welding current of 310 to 335 A and AC voltage of 31 to 33 V, welding speeds of 40 to 65cm/ minute can be achieved. The welding procedure employed for fabricating the spools is to apply a root weld and support runs using gas tungsten arc welding (GTAW, also known as tungsten inert gas welding or TIG welding), then filling with SAW. Joints are preheated to 180 to 200°C with infrared, followed by dehydrogenation heat treatment (DHT) at 250°C with electric resistance heating; post-weld heat treatment is carried out at 690°C in a gas- fired furnace. All welds are checked with Zetec Topaz TOFD (time-of-flight diffraction) and phased array ultrasonic testing (PAUT) systems. Claudio Perego, managing director of FAI Officine Di Carvico SpA, commented, “The ultrasonic scanning inspection method is more than severe, so we thought we might have difficulties achieving welds of a sufficiently high quality. However, the ESAB Aristo 1000 is very flexible, and the support provided by Vago Saldatura was superb, so the welds meet all of our requirements in terms of quality and productivity.”

WELDING and cutting technology firm ESAB has supplied a total of six submerged arc welding systems, including Aristo 1000 AC/DC inverter, to FAI Officine Di Carvico SpA, for fabricating high-pressure spools that are used in hydrocarbon flow lines. FAI specialises in the production of high-pressure vessels, pipeline components, sea water intake screening systems, reactors, and shell and tube heat exchangers. In addition to producing new fabrications, the company undertakes repairs. Given the nature of its work, FAI requires reliable welding systems that achieve high productivity and high quality, yet are sufficiently versatile to cope with a wide variety of base materials. Quality has been important to FAI Officine Di Carvico ever since it was established in 1961, and the company holds ASME stamps S, U and U2. The facility in Carvico, Italy, operates from a 14,000m 2 factory, with a further 40,000m 2 outside. Components up to 300 tonnes can be handled, with a maximum diameter of 6.5m and length of 60m. The specialist nature of the projects completed by FAI means that a variety of metals are used, ranging from carbon steel and low-alloy steel, most types of stainless steel (austenitic, ferritic, super-austenitic, duplex and super-duplex), to nickel

ESAB Group (UK) Ltd – UK Email: info@esab.co.uk Website: www.esab.com

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JULY 2019