The need for high-performing, corrosion-resistant alloys in oil and gas clad applications are increasing as more owner/operators move drilling operations offshore, into harsher conditions to tap petroleum reserves, which often contains more hydrogen sulphide (H2S).
Explosion Welding1 (EXW) a layer of corrosion-resistant alloys to carbon or low-alloy steel typically provides significant cost reduction for pressure vessels and other process equipment. Among all the existing nickel alloys, one specifically shows significant cost-benefit features: UNS N08825 (Alloy 825), a titanium stabilized Nickel-Iron-Chromium alloy. However, this nickel alloy is vulnerable to sensitization in a range of temperatures that is regularly used in equipment manufacturing processes.
NobelClad has partnered with VDM Metals to conduct a series of corrosion and mechanical tests throughout the manufacturing process to confirm that the cladding, head forming, vessel manufacturing, and lifecycle repair processes preserve the metals’ properties – both base and clad – from beginning to end. The study simulated and confirmed all heat treatments on the final clad product were successful.
The total project study focused on six suction and discharge drums. Each of them was built with two hemispherical heads and a number of shells. The H2S service and Stress Corrosion Cracking (SCC) from this specific oil and gas field required the equipment to be cladded with Alloy 825 to protect them from corrosion. In addition, the mechanical property requirements of the steel were relatively demanding. The Bill of Material (BOM) and technical specification can be summarized as follows:
Backer Steel: SA 516 Gr 65 as per ASME 5162
Additional requirement: Impact energy at -46°C, 34 J (min) and 41 J (Avg)
Cladder: Nickel Based Alloy UNS N08825 as per ASME 4243
Additional requirement: Corrosion test ASTM G28A4: 0.9 mm/y max
Additionally, the pressure vessels underwent Post Weld Heat Treatment (PWHT) at the end of the manufacturing stage:
Holding temperature and time: 600 – 625 °C (1112 – 1157 °F) for 210 min.
Heating and cooling rate: as per ASME Sec VIII