N6 nickel plate evaporator in caustic soda plant: 8 years zero corrosion record

Published by Engineering Team, Shaanxi Qianyi Tuoda Technology Co., Ltd on 2026-07-19

Into a caustic soda enterprise evaporator workshop in Shandong, A set of N6 nickel plate evaporator has been put into production since 2018, After 8 years of continuous operation, Overhaul disassembly detection plate wall thickness loss is small.Based on Baoji China titanium valley special material application practice, Combined with the complete working condition of the desensitization project, Material selection comparison, design points, operation and maintenance experience, Analysis of practical application value of N6 pure nickel material under high temperature concentrated alkali condition, Chlorine chloride, Provide reference for equipment selection in the lithium salt industry.

The enterprise is an annual output of 300,000 tons of ionic membrane caustic soda production enterprises, Evaporator as core equipment for production, The medium is 32% sodium hydroxide solution, Operating temperature 180℃ boiling state, atmospheric condition, Equipment 24 hours continuous operation, Perform annual minor repairs, A maintenance plan for a four-year overhaul.High temperature superimposition of concentrated alkali belongs to severe corrosion conditions, and it is difficult for ordinary stainless steel materials to serve stably for a long time.

316L stainless steel was used to make evaporator equipment in the early stage of the project.In the first year of service, stress corrosion cracks appeared at the weld joints.Pitting and perforation occurred in the tube plate of heating chamber in the second year;In the third year of operation, leakage occurred in many parts of the wall plate of the evaporation chamber, and the whole equipment was forced to be replaced as a whole.The core reason is that 316L stainless steel will have alkali embrittlement phenomenon in high temperature concentrated alkali environment, High temperature sodium hydroxide will destroy stainless steel passivation film, Accelerated corrosion failure.

Subsequent project replaced with N6 nickel plate evaporator, Stable operation for up to 8 years, three material advantage of pure nickel from N6 in high temperature concentrated alkali, The NiO passivation film formed by nickel in concentrated alkali environment is more stable than Cr ˇ O passivation film formed by stainless steel.N6 pure nickel is not easy to produce stress corrosion cracking in sodium hydroxide medium;The mechanical strength of the material under 180 ℃ working condition can meet the requirements of equipment use.Eight years field measurement, The original wall thickness of the plate is 6 mm, Overhaul inspection residual wall thickness 5.7 mm, Annual average corrosion rate <0.04 mm/year, According to the corrosion rate, the expected service life of the equipment can reach more than 15 years.

Key design details of this evaporator: the main body adopts 6mm and 8mm specifications N6 nickel plate combination;Argon arc welding is selected as welding technology, Supporting ERNi‑1 special nickel welding wire, Strictly control the temperature between welding layers not to exceed 100℃The heating chamber is equipped with N6 nickel tube and nickel tube plate, and the specification of heat exchange tube material is Φ38×2.5mm;The baffles are also made of N6 nickel plates, and the spacing between the plates is set to 300 mm;All bolts in contact with alkali liquor, nut, Flanges and other accessories are all made of nickel, Avoid the risk of galvanic corrosion caused by dissimilar metal contact.

Combined with eight years of on-site operation, Summarize three landing maintenance experiences, Equipment temperature rise and fall rate control is not greater than 30℃ per hour, Reduce thermal shock stressDaily monitor alkali concentration to maintain 30‑32% interval, avoid abnormal increase of concentration to produce crystallization;Ultrasonic thickness measurement shall be carried out every half year, wall thickness data shall be kept, and corrosion trend shall be tracked.

Comparison from a life-cycle cost perspective, The initial purchase cost of 316L stainless steel scheme is about 800,000 yuan, On average, it needs to be replaced every 3 years, The total investment of accounting for 20-year cycle is about 5.3 million yuanN6 nickel plate evaporator initial purchase about 2.6 million yuan, Designed service life of more than 15 years, The comprehensive cost of 20-year cycle is about 3.6 million yuan.Although N6 initial investment is higher, However, the total cost of life cycle accounting can be reduced by 32%, Reflect the long-term benefits of selecting suitable materials for strong alkali conditions.

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Frequently Asked Questions

Why is N6 nickel plate preferred for caustic soda production scenarios? N6 pure nickel for more than 30%, The corrosion resistance of concentrated alkali medium at high temperature of 150℃ and above is outstanding, Chlor-alkali industry evaporator, soda pan, Main flow structural materials for ion-exchange membrane electrolyzers.

What is the upper temperature limit for N6 nickel plate? N6 nickel plate melting point 1435‑1446℃, long-term use of the project is recommended not to exceed 300℃;Temperature over 300℃ material strength will drop significantly, should choose high temperature nickel-based alloy.

What other equipment is suitable for N6 nickel material? evaporator, soda pan, alkali liquor storage tank, ion-exchange membrane electrolyzer, Lye transfer pipeline, valve, The N6 nickel material scheme can be evaluated for equipment exposed to concentrated alkali medium such as pump body.

Can N6 and N4 nickel plates be interchanged under caustic soda conditions? N6 can be used under normal caustic soda conditions, and the procurement cost is reduced by 20‑30% compared with N4;N4 has higher purity and is mostly used in electronics and high-purity chemicals. N4 is generally not required for caustic soda scenarios.

data sources, Shandong caustic soda factory desensitization tracking measured data (2018‑2026), GB/T 2054‑2013 Nickel and Nickel Alloy Plates, Material Selection Manual for Chlor-alkali Industry Equipment disclaimer, This case has desensitized customer information, working condition in text, Cost data is only used as a reference for selectionPlease combine the actual project selection with the medium, temperature, pressure, Consult professional and technical personnel, Business rights and responsibilities are subject to a written contract duly signed by both parties.