N6 nickel plate: 80% weld leakage is sensitized corrosion-strong alkali scenario
Published by Engineering Team, Shaanxi Qianyi Tuoda Technology Co., Ltd on 2026-07-22
70% of nickel equipment failures in chemical industry are concentrated in sheet welds.
nickel plate surface appears chemically inert, But under strong alkali conditions, Sensitization corrosion is easy to occur in heat affected zone of weld seam, Many equipment leaks within five years of commissioning.This paper systematically explains the principle, production process, implementation standards and selection of N6
nickel plate materials, and recommends collection.
N6
nickel plate (
nickel plate/Sheet) is made of industrial pure nickel N6, Ni201, Hastelloy and other nickel-based materials as raw materials. It is formed by hot rolling, cold rolling, annealing and pickling. The thickness range of the plate is 0.5-100 mm.The delivery forms include hot rolled black sheet, cold rolled pickled AP sheet, and carbon steel + nickel layer explosive clad sheet.Hot rolled plate thickness 3-50mm, Cold rolled sheet 0.5-6mm, Nickel steel clad plate is composed of carbon steel base and pure nickel clad, Suitable for large equipment cost reduction.
Compare 316L stainless steel plate, TA2
Titanium Plate, Hastelloy C276 alloy plate, N6
nickel plate density 8.90g/cm³, tensile strength ≥380MPa;The service life can reach more than 20 years in a strong alkali environment with a concentration of 50% sodium hydroxide, and it has excellent resistance to high temperature molten salt;But in reducing acid condition corrosion resistance is general.Welding is difficult and sensitive to heat treatment sensitization.Compared to Hastelloy,, N6
nickel plate has obvious cost advantage, Nickel steel explosion compound technology mature, The equipment cost can be greatly reduced.
According to statistics of Nickel Branch of China Nonferrous Metals Industry Association, In 2024, the domestic market scale of N6 nickel plate is about RMB 600 million Yuan, Annual growth rate of 25%, Caustic soda and PVC industries together account for 70% of demand.Nickel steel explosive clad plate is the fastest growing, with the market share increasing from 8% in 2020 to 22% in 2024.
First, the core cause of N6 nickel plate failure
Strong alkali conditions, N6 nickel plate is the most cost-effective plate compared to Hardy C276, However, sensitized corrosion in HAZ is the biggest hidden danger., 80% of nickel plate equipment will leak at weld locations within 5 years.
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sensitized corrosionWhen the weld heat affected zone stays at 600-700℃, grain boundary precipitate carbide, Chromium-poor regions are formed, Intercrystalline cracking occurs continuously in high temperature and alkali medium.
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stress corrosionResidual stress in sheet metal stamping, Superposition of medium pressure and thermal stress, The stress corrosion rate can reach 5-10 times of that of ordinary corrosion.
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composite plate interface failureThe bonding interface of nickel steel explosive clad plate belongs to weak position, Insufficient shear strength, low recombination rate sheet, Layered blistering occurs after 1-2 years of production.
80% of nickel plate equipment failures are concentrated in weld seams, and 80% of weld failures are caused by sensitized corrosion.
Second, N6 nickel plate classification, material and performance
Divided by thickness: 0.05-0.5mm for nickel foil, mostly used for electrodes and composite substrates;0.5-3mm sheet for equipment lining, heat exchangers;3-25mm medium plate, used for reaction kettle shell, storage tank;25-100mm thick plate, suitable for PTA, marine, nuclear power equipment;Nickel steel explosion clad plate is composed of carbon steel base and nickel clad, which is suitable for large pressure vessels to reduce cost.
According to material classification: N6, Ni201, Ni200 industrial pure nickel, mainly strong alkali high temperature molten salt conditions;NCu30 Monel alloy suitable for hydrofluoric acid, seawater;Inconel600/625 for high temperature oxidizing environments;Hastelloy B/C276 is suitable for strong reducing acid;Nickel steel clad plate can save 40%-55% material cost.
The surface state is divided into hot rolling black skin, cold rolling pickling AP, bright annealing BA, sandblasting pretreatment, mirror polishing.
N6 chemical composition requirements Total nickel and cobalt content ≥99.5%, Carbon content is a key indicator of sensitization, N6 Carbon ≤0.10%, Low carbon Ni201 carbon ≤0.02%.Mechanical properties tensile strength ≥380MPa, yield ≥100MPa, elongation ≥35%, factory annealed state, bright annealing will slightly increase the cost.
III. Key points of manufacturing process
N6 nickel plate production core control sensitization interval, welding whole process high purity argon protection, composite plate strictly control interface bonding quality.
technological process, Vacuum Melting of
nickel ingot, homogenizing annealing, hot rolling, multi-pass cold rolling, stepped annealing, final annealing, acid passivation, Level Trim, ultrasonic nondestructive testing, identification, Vacuum nitrogen-filled packaging.
Key process points: heat treatment must avoid 600-700℃ sensitization interval;Only sulfuric acid and nitric acid mixed system is allowed in pickling, HF and HCl are strictly prohibited to prevent intergranular corrosion;The composite plate shall be tested by full-plate ultrasonic test, the composite shear strength shall be ≥ 196 MPa, and the composite rate shall be ≥ 98%;The flatness of the plate shall be controlled ≤2mm/m.The corrosion rate of sensitized area is 5-10 times higher than that of normal substrate.
IV. Standard system
GB/T2054 nickel and nickel alloy plate, GB/T5235 nickel alloy grade standard, composite plate reference YS/T719;NB/T47014 welding evaluation, NB/T47013 nondestructive testing for pressure equipment.ASTM B162 nickel plate specification is commonly used in the world, ASME SB-162 is used for pressure vessels, and ASTM G28 test is used for sensitization verification.
Important distinction: N6 suitable for normal temperature, 50% NaOH conditions;More than 70% high temperature high concentration caustic soda, must choose low carbon Ni201, can not be directly replaced by N6.
V. Application Scenarios and Selection Procurement Avoidance
N6 nickel plate is widely used in chlor-alkali evaporator shell, PVC stripper, Bayer process high pressure stripper, plating bath, Alkaline electrolyzer.Typical engineering case, 316L evaporator shell replaced by N6 nickel plate in caustic soda plant, Equipment life increased to more than 15 yearsThe PVC stripper uses N6 instead of Hastelloy C276, saving 60% of the project budget.
N6 nickel plate selection six-step method: the first step to confirm the medium, alkali concentration, temperature, chloride ion, sensitization risk;second, selecting N6 or Ni201;thirdly, completing the plate thickness design and reserving a welding seam corrosion allowance;step four, determine that length, width, thickness tolerance and flatness;The fifth step is to evaluate whether to select nickel-steel composite plates and review the composite strength;The sixth step is to agree on nondestructive testing and sensitization sampling.
The purchase contract shall specify the brand number, sheet size, flatness, supply state, Shear strength and recombination rate shall be indicated for composite plateClear implementation standards, RT/PT/UT test items, ASTM G28 Sensitization Retest, Warranty period 24 months, Supporting material certificate and flaw detection report.
Seven major quality risks shall be prevented in procurement: excessive sensitization caused by heat treatment at 600-700℃;Hydrochloric acid was selected to initiate intergranular corrosion;The welding seam is arranged at the position of scour and high temperature stress concentration;Nickel steel clad plate interface strength is insufficient delamination;The tolerance of plate thickness and flatness exceeds the standard;omitting sensitized corrosion test;Cross contamination of carbon steel leads to embedded corrosion of iron filings.
Domestic N6 nickel plate manufacturing technology is mature, Domestic manufacturers can stably supply 0.5-100mm full specification plate, Cost performance better than importsOnly nuclear power level 1 pressure, high-end special conditions imported products exist premium.
Material selection ideas: ordinary high temperature alkali N6;Ni201 is selected for high concentration and high temperature caustic soda;Hastelloy is selected for strong reducing acid condition;Large vessels give priority to nickel steel explosion clad plate cost reduction.
VI. Industry development trend
Three major directions for the future, Rapid popularization of nickel steel explosive clad plate, It is estimated that the proportion of composite plates will reach 50% by 2030Demand for large-sized and wide-width nickel plates continues to rise;Low-carbon Ni201 gradually replaces N6 to reduce the risk of sensitized corrosion.
Relying on the advantages of Baoji China Titanium Valley Industrial Cluster, Shaanxi Qianyi Tuoda Technology can supply N6 pure nickel plate, Ni201 nickel plate, nickel-steel explosive clad plate, Supporting material certificate, ultrasound, Penetrant Inspection Report, Suitable caustic soda, Aluminum chemical alkali equipment project.
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Data sources: GB/T2054, ASTM B162, nickel industry engineering application cases
disclaimer, present process, Selection parameters are only for technical reference, N6 nickel plate type selection of pressure equipment shall be reviewed by professional engineers, Determine the final technical plan based on project working conditions.