TPi January 2013

products & developments

Cladding performance Much effort is made by the pipeline industry to satisfy the needs to transport gas from far away regions to the final market and to set new solutions in terms of both design criteria and new high performance materials. Due to the fact that easy oil and gas is largely exploited, and new fields will be increasingly in deep and ultra-deep water (water depths greater than 500m and 1,500m, respectively), with higher pressures and temperatures and in more corrosive environments, material requirements are increasing.

array technique and creeping waves of longitudinal welds of clad pipes has been developed according to the ASME Code Sec V Art 4. After obtaining production process qualification by the customer, the effective production of longitudinal welded clad pipes started with the final selected materials to be delivered. Pipes are presently manufactured having a wall thickness ranging from 12mm (9+3) to 39mm (36+3) and a length typically of 6,000mm or 12,000mm. External diameters of the pipes typically are in the range of 12" to 36". The backing material of the clad pipes was ASTM A 516 Grade 60 and the clad resistance alloy (CRA) layers were both nickel alloys: Inconel 825 (UNS N08825) and Inconel 625 (UNS N00625). Due to the dimensional requirements arising by the on-site girth welding, pipes had to satisfy tight dimensional tolerances both in terms of out-of- roundness and internal diameter tolerance at pipe ends. With precise cutting of the ultrasonically tested plates, a careful weld edge preparation in accordance with the approved welding procedure provided necessary prerequisites for the cold forming of the pipes and the following welding processes. During cold forming of the pipes a step-by-step forming of the prepared plates into ‘slit pipes’ was carried out using a hydraulic brake press. The customer requests, in terms of elbows, are completed by Tectubi Raccordi with the manufacturing of clad elbows through cold forming, starting from the produced longitudinal welded clad pipes, and by hot forming and welding, starting from metallurgical clad plates.

nickel alloy welded pipes in the outside diameter range from 3" to 100", wall thickness from 3 to 60mm, and length up to 12m. Since last year Gieminox Tectubi Raccordi has devoted efforts to qualify the internal manufacturing process of welded clad pipes produced by forming hot-roll bonded clad plates for the supply of longitudinal welded clad pipes to be delivered to an EPC (engineering, procurement and construction) company. In order to qualify the welded joints and assess the quality of the produced welded pipes, a complete programme of characterisation was planned, taking into account the main requirements of the API 5LD and DNV OS F-101 standards. The characterisation was performed through metallurgical analysis, static and dynamic mechanical tests, fracture mechanic (CTOD) and corrosion tests. Regarding the longitudinal weld fabrication, in the case of backing material with higher thickness, longitudinal welding started in the C-Mn steel part from outside first by plasma arc welding (PAW) and after by multipass submerged arc welding (SAW). Filler materials are selected to guarantee in the fused zone mechanical properties not lower than the carbon steel base material (overmatching condition). Following the welding of CRA cladding inside (restoring) is performed. In the case of backing material with lower thickness, longitudinal welding starts in the inner part by (PAW) and from outside by gas tungsten inert gas (GTAW). A filler wire, usually in UNS N00625 material, is selected to guarantee the overmatching condition and the corrosion properties on the restored CRA layer. Because of the very stringent service conditions, it is mandatory during pipe production to guarantee a flawless welding quality. Therefore, considering also the peculiarities of the clad pipes in relation to non- destructive testing, a dedicated ultrasonic procedure for automated ultrasonic inspection with phased

In this situation low-alloy carbon steels tend to be structurally satisfactory, but lack in terms of corrosion resistance. On the other hand, stainless steels and nickel alloys resist corrosive environments, but lack in terms of strength, or are extremely costly. Clad pipe – low-alloy carbon steel with a thin layer of a corrosion-resistant alloy – is increasingly considered a suitable solution to the most demanding requirements of strength, corrosion resistance and cost-effectiveness. In a clad pipe, the (generally) unalloyed carbon steel outer pipe handles the internal and external pressure, while the high-alloy cladding provides the corrosion protection. Several manufacturing methods have been developed for producing clad pipes, including hot-roll bonding, explosive bonding and weld overlay. Many standards (such as API 5LD “Specification for CRA Clad or Lined Steel Pipe”, and DNV OS F-101 “Submarine Pipeline Systems”) have been developed, entirely or for some section, specifically for clad and lined pipes in which the liner pipe is fitted inside the outer pipe through a thermo- hydraulic manufacturing process. Lined pipes are manufactured by Gieminox Tectubi Raccordi welded pipes division, using its own designed and developed manufacturing process. A stable residual contact pressure is achieved by elastic and plastic behaviours of the outer pipe and inner pipe resulting in conformity with international standards API 5LD and DNV OS-F101. The company can produce longitudinal stainless-duplex-

Tectubi Raccordi SpA – Italy info@tectubiraccordi.com www.tectubiraccordi.com

Gieminox Tectubi Raccordi clad pipe

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January 2013 Tube Products International