ESAB Aristo 1000 submerged arc welding systems used by FAI

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ESAB has supplied a total of six submerged arc welding systems including Aristo 1000 ACDC Inverter to FAI Officine Di Carvico S.p.a. 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 also 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.

ESAB Aristo 1000 submerged arc welding systems used by FAIFAI Officine Di Carvico S.p.a. was established in 1961 and has continually expanded and invested to maintain its position as a market leader in its field. Quality has always been very important to FAI and today the company holds ASME stamps S, U and U2. Currently the facility at Carvico, Italy benefits from a 14,000m2 factory plus there is a further 40,000m2 outside. Components up to 300 tonnes can be handled, with a maximum diameter 6.5m and length of 60m.

The specialist nature of the projects completed by FAI means that a variety of metals are used; these range from carbon steel and low-alloy steel, though most types of stainless steel (austenitic, ferritic, super-austenitic, duplex and super-duplex), to nickel 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 S.p.a. has been using ESAB welding equipment and consumables since the early 1970s and one example of the type of system that plays a crucial role in FAI’s production is the ESAB Aristo 1000, six of which are used by FAI for submerged arc welding (SAW).

Bead Profile Modelling

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 1000AC/DC units can be connected in synchronised parallel mode.

FAI uses the ESAB Aristo 1000 power sources in conjunction with column-and-boom manipulators, normally with roller beds or positioners as well, 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 2 to 40 inches (50mm to 1 m) 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 1.54kJ/mm for diameters of 6 to 8 inches and 0.86 to 1.35kJ/mm for 14 inches and upwards. With a welding current of 310 to 335A and AC voltage of 31 to 33V, welding speeds of 40 to 65cm/minute are achieved. Furthermore, the Aristo 1000 reliably strikes a perfect arc every time, even in the worst-case conditions.

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 200degC with infrared, followed by dehydrogenation heat treatment (DHT) at 250degC with electric resistance heating, and post-weld heat treatment is carried out at 690degC 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, the Managing Director of FAI Officine Di Carvico S.p.a., comments: “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.”

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