Hangbo Alloy Group
Shanghai · Est. 2012
Subsea flowlines and risers face seawater, chlorides, and sour H2S. See which nickel alloys and copper-nickels resist corrosion and how Hangbo supplies them.
A subsea production system is a long, wet, pressurized metal labyrinth. Flowlines, risers, jumpers, and umbilicals carry untreated well fluids - seawater, brines, chlorides, CO2, and often hydrogen sulfide - from the seabed to a platform or FPSO. In that environment ordinary carbon steel corrodes in months, so the industry leans on corrosion-resistant alloys (CRAs): copper-nickels for seawater-wetted service and high-nickel austenitics and super-austenitics for the sourest, most chloride-rich duties. Getting the alloy right is a lifecycle-cost decision, not a line-item one.
Subsea hardware meets a stacked set of attack modes:
Our chloride stress corrosion cracking guide explains why nickel content is the single biggest lever against SCC in these systems.
Two alloy families do most of the work:
Where the produced fluid is genuinely sour, the selection logic converges with onshore sour-gas practice, covered in our sour gas and wet H2S service guide.
The defining constraint for a flowline or riser is the combination of chloride level, temperature, and H2S partial pressure. High nickel content - both in copper-nickels and in nickel-base CRAs - is what keeps pitting potential low and SCC risk manageable. Designers use NACE/ISO 21457 and operator-specific limits to map the service environment to an allowable alloy, and they almost always specify a higher nickel grade than a borderline carbon-steel route would permit, because the cost of a subsea failure dwarfs the material premium.
For the most aggressive sour-and-chloride duties, high-molybdenum nickel alloys such as Hastelloy C-276 are specified; our Hastelloy C-276 composition guide shows why the molybdenum-and-tungsten balance matters.
Subsea pipe is only as good as its welds. Long flowlines are reeled or laid in strings, so the alloy must tolerate cold work and repeated welding without losing corrosion resistance - meaning strict interpass control, qualified weld procedures, and often post-weld cleanliness checks for chloride-sensitive grades. Material is bought against stringent purchase specs with full traceability, hydrostatic and NDT records, and third-party inspection.
Because a single rejected weld can hold up a vessel spread costing six figures a day, buyers prioritize a supplier that holds tight composition and dimensional control across the whole order, not just the cheapest offer.
It depends on the duty. For seawater-wetted piping and cooling loops, copper-nickels such as 90-10 and 70-30 are standard thanks to their seawater resistance and anti-fouling behavior - see 90-10 cupronickel and 70-30 cupronickel. For higher-pressure, hotter, or sourer produced-fluid lines, nickel-base and super-austenitic corrosion-resistant alloys are specified instead.
Sour service is managed by raising nickel and molybdenum content and by applying NACE/ISO limits that map H2S partial pressure and chlorides to an allowable alloy. High-nickel CRAs resist sulfide stress cracking far better than carbon or low-alloy steel. The selection logic is detailed in our sour gas and wet H2S guide.
Copper-nickels dominate the seawater side: cooling water systems, firewater, ballast, and many externally seawater-exposed subsea and topside components, because they resist both corrosion and marine fouling. They are generally not used for the high-pressure sourer produced-fluid path, where nickel-base CRAs take over. See our 70-30 marine guide for the grade choice.
As a dedicated nickel alloy manufacturer serving marine, oil & gas sectors, Hangbo Alloy Group supplies the grades discussed here across all standard product forms with full ASTM/ASME documentation and EN 10204 3.1 certification. Our material is specified for applications where corrosion resistance, high-temperature strength, and traceable quality are non-negotiable. See our production & testing facilities for more on how every heat is verified.