Nickel 200 (UNS N02200) Technical Guide | High Thermal Conductivity & Caustic Soda Resistance
Date: 2024年11月18日 Categories: All Products、Nickel Views: 2025
Excerpt:
Nickel 200 (UNS N02200) technical guide from Hangbo Alloy. Differentiates commercially pure nickel from Nickel 201 on the 0.15% vs 0.02% carbon limit and the 600 °F (315 °C) ASME graphitization barrier, documents ~70 W/m·°C thermal conductivity, magnetostrictive properties, caustic soda and chlor-alkali corrosion performance, ASTM B162/B160/B161 forms, and a purchasing checklist plus FAQ.
Nickel 200 (UNS N02200) — Differentiating Commercially Pure Nickel from Nickel 201 for Caustic, Chlor-Alkali, and Specialty Service | Hangbo Alloy
Alloy Import Pitfalls Series — Technical Bulletin for Chemical, Electrochemical, and Electronic-Industry Buyers
The 0.02% Carbon Difference That Reshapes a Specification
Nickel 200 (UNS N02200) and Nickel 201 (UNS N02201) are both commercially pure nickel — nominally 99.0% minimum nickel plus cobalt. The only intentional compositional difference is carbon: 0.15% maximum for Nickel 200 versus 0.02% maximum for Nickel 201. That single element, and the operating temperature at which it becomes dangerous, is the entire basis of the specification decision between them — and it is exactly the distinction that gets lost when a supplier's catalog, certificate, or (as Hangbo Alloy has seen on more than one competitor's web page) product literature confuses the two grades.
This page is the engineering-grade differentiation document for Nickel 200, supplied by Hangbo Alloy (Shanghai Hangbo Alloy Group, nickel-alloy.com). If you are handling caustic soda above roughly 300 °C, reading this page before issuing the PO could save you from a graphitization failure that no tensile test would have predicted.
1. Chemistry and Identity — What "Commercially Pure" Really Contains
| Element | Nickel 200 (N02200) | Nickel 201 (N02201) | Import Watch-Point |
|---|---|---|---|
| Nickel (+ Cobalt) | 99.0 min | 99.0 min | Cobalt counts as nickel in most specs |
| Carbon | 0.15 max | 0.02 max | The grade discriminator — verify on MTC |
| Iron | 0.40 max | 0.40 max | |
| Manganese | 0.35 max | 0.35 max | |
| Copper | 0.25 max | 0.25 max | Distinguishes from Monel 400 (Cu 28–34%) |
| Silicon | 0.35 max | 0.35 max | |
| Sulfur | 0.01 max | 0.01 max |
Nickel 200 is single-phase FCC, non-hardenable by heat treatment, and magnetic at room temperature. Crucially for the differentiation story, pure nickel is not an alloy of the Monel or Inconel type — it has no chromium to form a passive film and no copper addition for seawater or hydrofluoric service. Its corrosion credentials are specific: caustic alkalies, reducing and neutral media, and selected high-temperature applications below the graphitization window.
| Physical Property | Nickel 200 | Nickel 201 | Engineering Consequence |
|---|---|---|---|
| Density | 8.89 g/cm³ | 8.89 g/cm³ | Same — density cannot identify grade |
| Melting range | 1435–1446 °C | 1435–1446 °C | Same |
| Curie temperature | ≈ 360 °C (680 °F) | ≈ 360 °C (680 °F) | Loses ferromagnetism above ~360 °C |
| Thermal conductivity | ~70.3 W/m·°C at 20 °C; ~66.5 at 100 °C | Equivalent | ~4–5× stainless steel |
| Electrical resistivity | ~8.5 µΩ·cm at RT | Equivalent | Excellent electrical/electronic use |
| ASME max service temp (pressure parts) | 600 °F (315 °C) | 1250 °F (677 °C) | Carbon-driven code limit |
2. Thermal Conductivity — The Heat-Transfer Argument for Pure Nickel
Nickel 200's thermal conductivity of roughly 70 W/m·°C at room temperature places it far above the austenitic stainless steels (typically 15–16 W/m·°C) and above many nickel-chromium alloys (Inconel 600 ≈ 15 W/m·°C; Monel 400 ≈ 22 W/m·°C). In caustic evaporators, reborn caustic concentrators, and heat exchangers where product-side fouling is not the limiting factor, pure nickel construction transfers heat with dramatically less surface area or temperature differential than stainless alternatives.
| Material | Thermal Conductivity at 20–100 °C (W/m·°C) | Relative Heat Transfer |
|---|---|---|
| Nickel 200 / 201 | ~70 / ~66 | ~4.5× stainless |
| Carbon steel | ~54 | ~3.5× stainless |
| Monel 400 | ~22 | Reference Ni-Cu |
| Type 304/316 stainless | ~15–16 | Baseline |
| Inconel 600 | ~15 | Baseline class |
The import pitfall here is subtle: because Nickel 200 and 201 share identical thermal properties, a supplier "upgrading" a 201 heat-exchanger order to 200 — or vice versa — changes nothing on the heat-transfer calculation. It changes everything on the temperature limit (Section 4). Never accept a conductivity argument as evidence that grade substitution is benign.
3. Magnetostriction and Specialty Physical Properties
Pure nickel is the classic magnetostrictive material: it changes dimension in response to a magnetic field (and changes magnetization in response to stress, the inverse effect). Saturation magnetostriction for polycrystalline nickel is negative, on the order of −30 to −40 ppm. This property, combined with high permeability and a well-defined Curie temperature near 360 °C, underpins Nickel 200/201's role in:
- Ultrasonic transducers and sonar delay lines (nickel magnetostrictive elements),
- Magnetic shielding and relay/reed components requiring high saturation flux,
- Precision instruments exploiting the linear magnetostriction region at low field,
- Electronic tubes and battery components where purity and controlled magnetic response matter.
Two engineering cautions for buyers: (1) the magnetostrictive response is essentially identical between Nickel 200 and 201, so grade choice in these applications is driven by processing temperature, not magnetism; and (2) cold work alters magnetic properties — specify the temper (annealed vs. cold-drawn) if magnetic performance is functional, and verify with the mill that the product was not deliberately alloyed. Any chromium, copper, or iron pickup in "pure" nickel degrades both conductivity and magnetic behavior.
4. Caustic Soda (NaOH) Resistance and the 300 °C Barrier
The crown jewel of pure-nickel corrosion resistance is performance in caustic soda — all concentrations from dilute through the molten state. The mechanism is a black, adherent nickel-oxide surface film that forms during exposure and progressively lowers the corrosion rate over long service. This is the film that makes nickel the standard metallurgy for caustic evaporation and concentration, and it is the property that pure nickel — not Monel 400, not the 800 alloys — delivers best in hot strong alkali.
| Environment (NaOH) | Temperature | Corrosion Rate | Engineering Comment |
|---|---|---|---|
| 50% solution, laboratory | 30 °C (86 °F) | ~0.06 mpy (0.0015 mm/a) | Negligible |
| 50% solution | 90 °C (195 °F) | ~0.7 mpy (0.018 mm/a) | Very low |
| 50% solution, boiling | ~100 °C (212 °F) | ~0.1–0.7 mpy | Very low; film forms |
| 50% solution | 130 °C (266 °F) | ~1.1 mpy (720-h test) | Low |
| 50% solution | 150–155 °C (302–310 °F) | ~0.4–0.5 mpy | Stable, film-protected |
| Concentrating evaporators (30→50%, plant) | Evaporating | ~0.16 mpy | Film-controlled |
| 70–75% solutions | Up to ~200 °C | ~0.02–1.0 mpy | Rising with temperature |
| Molten NaOH | 350–450 °C | Low rates in clean melt | Use Nickel 201 above 315 °C |
The 300 °C barrier — where 200 and 201 finally diverge. At temperatures above roughly 315 °C (600 °F), the carbon dissolved in Nickel 200 can precipitate at grain boundaries as graphite — a catastrophic, embrittling, creep- and corrosion-degrading reaction (the process is variously called graphitization or carbon rejection). The ASME code therefore caps Nickel 200 pressure-boundary service at 600 °F, while Nickel 201 — with carbon limited to 0.02% — is code-recognized to 1250 °F (677 °C). Every caustic concentrator, reborn-caustic line, and molten-caustic component operating above 300 °C must be specified as Nickel 201, not 200. If your supplier's page publishes "Nickel 200: excellent for caustic to the melting point" without the carbon/temperature caveat, the literature is wrong and the order is at risk.
Two accelerants deserve a footnote in any caustic specification: chlorates in the caustic raise corrosion rates measurably and should be minimized, and oxidizable sulfur compounds increase corrosivity (treating with sodium peroxide to oxidize them to sulfate counteracts the effect). Chlor-alkali producers who feed membrane-cell caustic with residual chlorate into nickel evaporators should model this explicitly.
5. Chlor-Alkali Cells: Where Pure Nickel Earns Its Keep
In chlor-alkali plants (membrane, diaphragm, and mercury-cell processes), nickel is the engineering material of the caustic side: evaporators, concentrators, coolers, storage, and the piping that moves 30–50% (and higher) caustic at temperature. Nickel 200/201's qualifications are:
| Duty | Material Practice | Why |
|---|---|---|
| Brine treatment & cells (electrolyzer hardware) | Titanium/nickel per cell design | Nickel resists caustic catholyte; titanium handles anolyte chlorine |
| Caustic evaporators & concentrators | Nickel 201 above ~300 °C shell/tube | Graphitization cap forces 201 at high temperature |
| Caustic cooling & storage | Nickel 200/201, or clad | Below 300 °C either grade works |
| Chlorine handling (dry) | Carbon steel / specific alloys | Wet chlorine requires higher-Cr alloys, not pure nickel |
| Oxidizing chloride bleach streams | Avoid pure nickel above ~500 ppm available chlorine | Oxidizing chlorides attack nickel rapidly |
Nickel's resistance to caustic stress-corrosion cracking and its clean, low-contamination surface (critical for rayon-grade and food-grade caustic) reinforce the selection. But note the boundary conditions: pure nickel must be kept out of oxidizing acid chlorides (ferric, cupric, mercuric) except at low concentration, and continuous exposure to oxidizing alkaline chlorides should not exceed roughly 500 ppm available chlorine. The "nickel for everything in chlor-alkali" myth — usually traceable to a page that conflates nickel with the chromium-bearing alloys — is a corrosion incident waiting to happen.
6. Mechanical Properties and Product Forms
Pure nickel work-hardens rapidly, so product is sold annealed, and strength is modest by design — ductility and corrosion integrity, not strength, are the selection drivers.
| Form / Condition | Tensile Strength | Yield Strength (0.2%) | Elongation | Hardness |
|---|---|---|---|---|
| Annealed rod/bar (typical) | 380–520 MPa (55–75 ksi) | 105–210 MPa (15–30 ksi) | 55–40% | 90–120 HB |
| Hot-finished / as-rolled | 450–600 MPa | 150–350 MPa | 45–25% | Higher with work |
| Annealed plate (typical) | 345–550 MPa | 100–300 MPa | 60–30% | — |
| Product Form | ASTM | Hangbo Alloy Supply Range |
|---|---|---|
| Plate, sheet, strip | B162 | Plate to 100 mm, sheet to 3000 mm wide |
| Rod and bar | B160 | Ø 3–500 mm |
| Seamless pipe and tube | B161 / B163 (HEX tube) | Pipe to 12" NB |
| Forging stock | B564 | Billets, rings, blocks |
7. Purchasing Checklist — Keeping 200 and 201 (and Monel) Apart
| Check | Acceptance Criterion |
|---|---|
| UNS on MTC | N02200 for 200; N02201 for 201; N04400 is Monel — different alloy entirely |
| Carbon | ≤0.15% for 200; ≤0.02% for 201 — always on certificate |
| Copper | ≤0.25% — a copper figure near 30% means Monel, not nickel |
| Service temperature declared | >300 °C caustic → specify 201; ≤300 °C → 200 acceptable |
| Product spec | B162/B160/B161 per form — never a generic "nickel" callout |
| Optional tests | Carbon re-check at arrival; PMI; hardness for temper verification |
Technical FAQ — Nickel 200 (UNS N02200)
1. What is the difference between Nickel 200 and Nickel 201?
Carbon content: Nickel 200 allows 0.15% max carbon, Nickel 201 limits it to 0.02% max. Above ~315 °C (600 °F), Nickel 200 risks grain-boundary graphitization and is code-limited to 600 °F, while Nickel 201 serves to 1250 °F (677 °C). Below 300 °C their corrosion and mechanical behavior is essentially equivalent.
2. Why is Nickel 200 preferred over stainless steel for caustic soda service?
Pure nickel resists all concentrations of caustic soda including the molten state, protected by a black nickel-oxide film, and is not susceptible to chloride stress-corrosion cracking. It also avoids the caustic/chloride cracking and contamination issues that limit stainless and nickel-chromium alloys in hot strong alkali. Nickel 200 is thus standard for caustic evaporators, concentrators, and storage.
3. What is the maximum service temperature of Nickel 200 in caustic service?
For pressure-boundary and structural service, ASME limits Nickel 200 to 600 °F (315 °C) because of graphitization risk. For caustic equipment above 300 °C — for example molten-caustic and high-concentration evaporator duty — specify Nickel 201 (N02201). Hangbo Alloy will not certify Nickel 200 for code service above that limit.
4. Is Nickel 200 magnetic, and what is its Curie temperature?
Yes — pure nickel is ferromagnetic at room temperature with a Curie temperature near 360 °C (680 °F); above that it becomes paramagnetic. Its negative magnetostriction and clean magnetic response are exploited in ultrasonic transducers, magnetic shielding, and precision instruments. Cold work affects magnetic properties, so state the temper if magnetic behavior is functional.
5. What is the thermal conductivity of Nickel 200?
Approximately 70 W/m·°C at 20 °C, falling to about 66 W/m·°C at 100 °C — roughly four to five times that of 304/316 stainless steel and about three times that of Monel 400. This drives its use in caustic heat exchangers and evaporator tubing where heat transfer, not strength, governs surface area.
6. Can Nickel 200 be used in chlor-alkali plants?
Yes — it is the reference material for the caustic side: evaporators, concentrators, coolers, and caustic piping. Keep it out of oxidizing chloride environments (limit ~500 ppm available chlorine in oxidizing alkaline chlorides) and away from wet-chlorine anolyte duty, where chromium-bearing alloys or titanium are required. For equipment above 300 °C, move to Nickel 201.
7. Why does my "Nickel 200" certificate need a carbon value at all?
Because carbon is the only compositional lever that separates N02200 from N02201 — and because a certificate without a carbon figure cannot prove which grade you received. An arrival carbon check is the definitive grade-verification test for pure-nickel products.
8. Is Nickel 200 resistant to hydrochloric and sulfuric acids?
Pure nickel is not the first choice for acid service. It resists non-oxidizing media well under many conditions, but aerated or oxidizing acids attack it. For hydrofluoric acid, Monel 400 is the classic nickel-family choice; for hot reducing acids, molybdenum-bearing alloys such as the C-types perform better. Select on the specific acid, temperature, and aeration.
9. What ASTM specifications govern Nickel 200 plate, bar, and pipe?
ASTM B162 (plate/sheet/strip), ASTM B160 (rod/bar), and ASTM B161 (seamless pipe/tube), with B163 commonly applied to heat-exchanger tubing and B564 to forgings. ASME SB equivalents exist. Always couple the UNS grade with the product-form specification on the purchase order.
10. Does Hangbo Alloy supply both Nickel 200 and Nickel 201 with guaranteed grade integrity?
Yes. Hangbo Alloy stocks and certifies both N02200 and N02201 across plate, bar, pipe, and forgings, with EN 10204 3.1 mill certificates showing carbon and copper on every heat, in-house PMI, and optional third-party arrival inspection. We also advise on grade selection when your service temperature crosses the 300 °C graphitization boundary — because that advice is where the real value of a specialty supplier shows.
Alloy Import Pitfalls Series — Hangbo Alloy (Shanghai Hangbo Alloy Group, nickel-alloy.com). Property and corrosion data are typical engineering values compiled from recognized industry sources for material selection; governing documents are the applicable ASTM/ASME specifications and code rules. Contact Hangbo Alloy for Nickel 200/201 stock, certificates, and application engineering support.
