N6 nickel tube: strong alkali scene

N6 nickel tube purchase unit price looks 5 times more expensive than titanium, But in strong alkali, high-temperature molten salt, Under causticizing condition, Titanium cannot withstand corrosive environments, N6 nickel tube can be stable service.This paper systematically explains the material characteristics, production process, implementation standards and selection points of N6 nickel tube, and recommends collection.

N6 Nickel Tube raw material is industrial pure nickel N6, Total Ni and Co content ≥99.5%, hot extrusion, cold rolling, anneal, pickling, processing and forming, Finished product diameter φ6-φ325 mm.Supply form includes bright cold drawn annealed seamless pipe, heat exchanger special U bend, immersion cooling coil.

316L stainless steel tube, TA2titanium pipeHastelloy C276 alloy pipe, N6 nickel pipe density 8.90g/cm³, tensile strength ≥380MPa;The service life can reach more than 20 years in 50% sodium hydroxide strong alkali environment, Excellent high temperature molten salt resistanceBut in dilute sulfuric acid such as reducing acid environment corrosion resistance is general.Welding requires double-sided high-purity argon protection, very sensitive to heat treatment sensitization, procurement costs higher thantitanium pipeLower than Hastelloy.

According to statistics of Nickel Branch of China Nonferrous Metals Industry Association, In 2024, the domestic market scale of N6 nickel tube is about CNY 800 million, Annual growth rate of 22%, Caustic soda and PVC industries account for 65% of total demand, It is the main application field of N6 nickel pipe.

Chemical scene,titanium pipeSuitable for wet chlorine, seawater, dilute acid medium, 316L for ordinary acid and alkali environment.But high temperatures and high concentrations of caustic soda, NaOH≥50%, Temperature ≥150℃, N6 nickel pipe and Hastelloy C276 pipe are the only two kinds of pipes in long-term stable service.The price of HACCP C276 is three times higher than that of N6, so N6 becomes the best choice for strong alkali operation cost.

N6 nickel tube material is stable, but the weld is the weak link.Nickel material annealed at 600-700℃ will be sensitized and carbide precipitated at grain boundaries, resulting in intergranular corrosion.90% of the early leakage of N6 nickel pipe is caused by sensitized corrosion superimposed stress concentration cracking in heat affected zone of weld.Sensitization control is the key point of N6 nickel pipe production and welding.

According to the production process, seamless pipe extrusion + cold rolling process, φ6-φ219mm, wall thickness 0.5-25mm, mostly used for caustic soda concentration, PVC stripping pipeline;Thick wall extruded cross-rolled pipe diameter φ114-φ325mm, wall thickness 10-50mm, suitable for high pressure reactor;U-bend after cold bending and annealing, used for tube heat exchanger;Coil for immersion cooling;Nickel strip coil welded pipe is suitable for low pressure general chemical pipeline.

According to wall thickness, D/t≥20 is thin-walled heat exchange tube;D/t in the range of 10-20 is the general chemical pipe with middle wall;D/t4-10 is high pressure thick wall pressure pipe.

N6 material chemical composition requirements Nickel cobalt sum ≥99.5%, Carbon content ≤0.10%, the higher the carbon content, The greater the risk of sensitization.Mechanical properties: tensile strength ≥380MPa, yield ≥100MPa, elongation ≥35%, factory annealed state;Bright annealing increases material costs slightly.

N6 nickel pipe production andtitanium pipeThe biggest difference between stainless steel is sensitivity control, strict control of annealing temperature, and argon protection throughout welding. complete process flow, nickel ingot smelting, homogenizing annealing, high-temperature extrusion, deep-hole drilling, multipass cold rolling, intermediate annealing, final annealing, acid passivation, Ultrasonic eddy current nondestructive testing, cutting to length, identification, Vacuum nitrogen-filled packaging. Process control core: heat treatment must avoid 600-700℃ sensitization interval;Acid pickling can only use sulfuric acid and nitric acid mixed system, hydrofluoric acid and hydrochloric acid are strictly prohibited to prevent intergranular corrosion;Bend must be annealed after processing;The finished product needs 100% eddy current testing, and the chloride ion of water for hydrostatic test is controlled within 25ppm. Sensitization is the greatest risk of N6 nickel tubes, and the corrosion rate of sensitized areas is 5-10 times that of normal substrates.

Domestic reference GB/T2882 nickel and nickel alloy pipe, GB/T5235 processing nickel and nickel alloy brand standard, pressure equipment matching NB/T47014 welding evaluation, NB/T47013 nondestructive testing specifications.ASTM B161 Nickel Seamless Pipes are commonly used internationally, and ASME SB-161 is adopted for pressure vessel projects. Key distinction grade: N6 for normal temperature, 50% NaOH conditions;More than 70% high temperature caustic soda environment, need to choose low carbon Ni201, can not be replaced by N6.

N6 nickel tube is widely used in chlor-alkali caustic soda evaporator, PVC stripper overhead line, Bayer process stripping equipment in aluminum plant, Plating circulation lines.Typical project case: caustic soda plant 50% NaOH evaporator replacement 316L, the use of N6 nickel pipe life increased to more than 15 years;PVC plant uses N6 instead of Hardy C276, reducing project cost by 60%.

Six-step method for N6 nickel tube selection: The first step is to confirm the medium, alkali concentration, temperature, and chloride ions;second, selecting N6 or Ni201;third, determining the pipe use, heat exchange or process pipeline;step four, determine that tolerance of the outer diameter wall thickness length;The fifth step is to agree on PT and eddy current nondestructive testing;Step 6: Conduct ASTM G28 sensitization sampling inspection as needed.

The purchase contract shall specify the brand number, size, supply state, ovality requirement, Post-bend annealing requirements, executive standard, Nondestructive testing project, sensitization test, Warranty period 24 months, Supporting material certificate, Flaw detection report.

Five major quality risks shall be prevented during procurement: excessive sensitization caused by heat treatment at 600-700℃;Hydrochloric acid was selected to initiate intergranular corrosion;Annealing is omitted after bending, and the bending position is cracked;Ni201 was replaced by N6 under the condition of high temperature and high concentration alkali.Critical pipes lack 100% eddy current and penetration testing, and defects are missed.

Domestic N6 nickel tube manufacturing technology is mature, Domestic manufacturers can stably supply φ6-φ325mm full specification products, Cost performance better than importsOnly nuclear power level 1 pressure, high-end special projects import products exist premium.

Material selection ideas: ordinary high temperature strong alkali conditions choose N6;Ni201 is selected for high concentration and high temperature caustic soda;Hastelloy is selected for strong reducing acid corrosion condition.

Caustic soda production capacity continues to expand, N6 is used instead of Hastelloy to reduce cost in PVC installation, Driving the demand for N6 nickel tubes to riseAt the same time, the market demand for large-sized φ325mm thick-walled nickel pipes continues to grow.

Relying on the advantages of Baoji China Titanium Valley Industrial Cluster, Shaanxi Qianyi Tuoda Technology can supply N6 Nickel Seamless Pipe, nickel U-tube, nickel welded pipe, Supporting material certificate, eddy, Penetrant Inspection Report, Suitable caustic soda, Aluminum chemical industry and other strong alkali conditions project.

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