Introduction
Arvedi Tubi Acciaio (ATA), one of the first companies of the Group founded by Giovanni Arvedi, started up in 1973 with the production of carbon steel welded tubes at its Cremona works where it came into being as a company aiming at a product for special applications using modern technology to serve the market with the highest possible flexibility and quality.
 The first production plant dates back to 1973 when the stretch reducing mill (SRM) was installed downstream from a high frequency welding machine (ERW), an absolute novelty in Italy. Starting with black and galvanised gas and water pipe production with the trademark Arvedi LC (hot rolled), in the course of two years it was able to propose a new product, GSM, heavy wall hot reduced tube for specialist applications.
With GSM tube, much more precise and uniform than seamless tube, it acquired increasingly important market shares in the mechanical tube and cold drawn finished tube sectors.
ATA currently produces about 350,000 tpy of carbon steel welded tubes, almost a third of which are produced on the SRM, with 470 employees, a quarter of which are employed on the SRM.
The company produces carbon steel welded tubes in the diameter range from 17 to 168.3 mm, in wall thicknesses from 1.2 to 11 mm. Within this range the SRM produces the whole range of tubes in diameters from 17 to 88.9 mm in wall thicknesses from 1.8 to 11 mm.
ATA exports over 40% of its production, mainly onto the European quality tube market.
 The hot rolled tube production cycle
The raw material is in the form of carbon steel coils which are first cut longitudinally on special slitting lines in order to obtain strips, the width of which corresponds to the diameter of the tube to be obtained.
The strips, loaded onto longitudinal forming and welding lines, are unwound and through a series of paired rolls progressively curved transversally until they assume a profile close to a semi-closed circular section with the edges, after heating by a high frequency electric current, touching and pressed to generate the continuous welding.
The welded tube is cut and placed on a bench, the accumulation “lung” holding up to 50 tubes, placed between the welding line and the hot rolling mill; these tubes, called “mother shells”, are each about 200 metres long.
Downstream of this welding plant is the hot rolling mill. The hot rolled tubes are obtained with the plant with which ATA has been equipped since the start of its activity and is unique in Italy; the mother shell, over 200 metres long and heated in an electric induction heater, is hot reduced in the stretch reduction mill (SRM) in order to obtain the final dimensions required.
The heater is an induction furnace with a total installed power of 15 MW; the mother shell enters at ambient temperatures and leaves at about 1000°C, the temperature necessary for the subsequent rolling phase.
The heart of the plant is the SRM, built by Danieli on an Etna Standard patent.
The mill has 20 individually-driven rolling stands that can be set to a wide range of speeds.
This characteristic makes the Arvedi SRM particularly flexible and suitable for the production of tubes with very thick walls in relation to the diameter.
The rolling stands, with 3 rolls for a maximum entry diameter of 115 mm, are mounted on the rolling mill with orientation staggered to 180° and obtain progressive reduction of the tube diameter, stretching the tube by increasing the speed from stand to stand.
When rolling with high reductions, the diameter of the mother shell is reduced 5-6 times with elongations of 7-8 times.
Downstream of the SRM the plant is completed with various finishing lines.
 Characteristics of Arvedi hot rolled tubes
In particular the GSM (heavy wall) product is characterised by its particular metallurgical and crystalline properties, being obtained from a production cycle which provides rolling of the strip (the mother shell’s starting material) and subsequent hot rolling which orients the steel fibres in the most suitable way through the effect of the stretching.
The hot rolling production cycle (HFW + SRM) makes the tube excellent for both cold and hot processing (it is supplied in a state similar to normalised) and with precision characteristics higher than those of tube obtained through the seamless cycle.
The particular typology of the Arvedi plant allows a product to be manufactured, for all the wall thicknesses in the manufacturing range, according to user specifications, i.e. to customise the product in all its particular aspects (steel grade, diameter, wall thickness and length).
GSM tube, in fact, is a tube with better wall thickness tolerances than seamless tube and with limited eccentricity as it is produced from a tube made from a welded strip.
 “Where eccentricity is defined as the disalignment between the tube’s outside diameter axis and its internal diameter axis “
GSM tube can be produced with very low diameter/wall thickness ratios, down to 3.5 ÷ 4, ratios difficult to achieve with a welded tube, while maintaining good internal surface polygonality.
“Where polygonality is defined as the facetting of the internal tube surface “
GSM tube presents a smooth internal surface without the welding bead, even for small diameter and heavy wall products, as it is rolled from a large diameter welded tube from which the bead has been removed. GSM is therefore suitable for cold drawing and for all mechanical processings which require a good internal tube surface.
Moreover, GSM tube is also produced in steel grades with high mechanical characteristics, even for small diameter and heavy wall products, since hot rolling allows the wall thickness to be increased with respect to the wall thickness of the mother shell.
Synergy with Acciaieria Arvedi allows it to develop new products made with special steels and aimed at specific projects. The production line from the steel to the finished and pre-processed tube responds with ideas and solutions, even personalised ones, to the most varied demands.
 Hot rolling mill products
Hot rolled tubes, in the 1970s given the name ''Arvedi LC '', are differentiated into two large families: GSM tubes for drawing and mechanical applications, better defined hereafter, and gas and water pipe.
Tubes for boilers and high temperature applications, line pipe and oil industry applications are also produced.
As regards the types of steel grades, alongside the standard carbon construction steels, interesting percentages of tubes are produced in carbon, alloyed and boron steel with higher strength mechanical characteristics.
GSM tubes for mechanical applications
The peculiarities of the stretch-reducing machine, the first of which is the possibility of obtaining heavy wall hot rolled special steel tubes in medium/small diameters without the welding bead, have allowed ATA to expand into the field of tubes for mechanical applications. The excellent processability of the products, besides a wide range of steel grades used, allows GSM tubes to be used in traditional mechanical applications and in specific sectors. Of particular interest is the product range destined for:
- mother shells for cold drawing;
- tubes for boilers and high temperature applications;
- reinforcement anchorages in tunnels and mines.
 Controls and product certifications
ATA’s quality management system, certified since 1987, has been progressively perfected so as to attain maximum efficacy and consequently ensure product quality with the lowest possible impact on the environment.
A multi-functional working group has developed a series of general control plans to ensure product conformance with national and/or international standards and specific control plans for tubes made on the basis of the customer’s technical specifications.
The control process flow-chart examines all the phases, from receiving the raw material in the form of steel coils to the final storage phase of the ready-to-ship product. Checks and controls are carried out both on the process parameters and on the product characteristics using a series of modern equipment installed along the processing cycle.
ATA’s whole production range is approved and qualified by important external authorities. In particular, Arvedi LC (hot rolled) tube is qualified by product certification for the following applications indicated in the table.
By Arvedi |
