Introduction: Nickel 200 and 201 — The Pure Nickel Paradox
Nickel 200 (UNS N02200, EN 2.4066) and Nickel 201 (UNS N02201, EN 2.4068) constitute the most elemental offering in any nickel-alloy supplier’s catalog: commercially pure nickel, with a minimum 99.0% Ni content and no deliberate alloying additions. They form the foundation of the nickel product pyramid — below alloyed grades like Monel and Inconel, yet above stainless steel in corrosion resistance for specific chemistries.
The paradox is this: the two grades are chemically nearly identical. Their nominal Ni, Fe, Mn, Cu, Si, and S contents are the same. Ask a mill to ship you the “wrong” one and you may struggle to tell the difference in an OES spark analysis — because the distinguishing element, carbon, differs by barely 0.13 percentage points.
And yet, that 0.13% carbon gap determines whether your pressure vessel survives 20 years or fails by intergranular graphite embrittlement in under 12 months above 315 °C. This article explains the metallurgical mechanism, maps the applications where carbon matters, and provides a step-by-step decision flow for choosing between Nickel 200 and Nickel 201 across the full service envelope.
For a broader perspective on how pure nickel grades fit into the alloy landscape, see our nickel alloy vs stainless steel comparison.
1. Chemical Composition: One Element Reigns Supreme
| Element | Nickel 200 (N02200) | Nickel 201 (N02201) | Why It Matters |
|---|---|---|---|
| Ni + Co | ≥ 99.0% | ≥ 99.0% | Base purity — identical |
| C | ≤ 0.15% | ≤ 0.02% | Defining difference — 7.5× lower |
| Fe | ≤ 0.40% | ≤ 0.40% | Comparable |
| Mn | ≤ 0.35% | ≤ 0.35% | Comparable |
| Cu | ≤ 0.25% | ≤ 0.25% | Comparable |
| Si | ≤ 0.35% | ≤ 0.15% | Slightly lower in 201 |
| S | ≤ 0.010% | ≤ 0.010% | Hot-workability control |
Every other element in the specification is a residual — an impurity carried over from the electrolytic or carbonyl refining process. There are no deliberate alloying additions beyond the nickel itself. This makes Nickel 200/201 unique among engineering alloys: their properties are the properties of nickel itself, undiluted and unmodified by alloying elements.
The Carbon Story
The 0.13% carbon difference is not a production cost-saving measure. It is not a reflection of “better” vs “worse” nickel. It is a deliberate metallurgical design choice rooted in an inconvenient physical fact: carbon is soluble in nickel above approximately 650 °C, but precipitates out as graphite at intermediate temperatures (approximately 425–650 °C). The 0.02% carbon ceiling in Nickel 201 suppresses this precipitation to levels that are metallurgically benign, opening a 425–650 °C service window that is completely closed to Nickel 200.
2. The Metallurgy of Graphite Embrittlement
The Mechanism
In pure nickel, carbon exists in interstitial solid solution at temperatures above roughly 650 °C. When Nickel 200 with 0.05–0.15% C is held in the 425–650 °C range — or even slowly heated through it to higher temperatures — the carbon diffuses to grain boundaries and precipitates as graphite (elemental carbon, NOT chromium carbide) .
Unlike the M₂₃C₆ chromium carbides that cause sensitization in stainless steels, graphite precipitation in pure nickel is an irreversible microstructural transformation. Once precipitated, graphite does not re-dissolve at higher temperatures on commercially practical timescales, because the kinetics of re-dissolution are limited by the need to break C‒C covalent bonds.
Mechanical Consequences
The graphite precipitates at grain boundaries act as micro-voids, creating:
- Severe loss of ductility. Elongation can drop from 40–50% to single digits after as little as 500–1,000 hours of exposure at 550 °C for Nickel 200. Charpy impact values at room temperature can fall by 50–80%.
- Intergranular fracture mode. At room temperature, embrittled Nickel 200 fractures along grain boundaries rather than by ductile microvoid coalescence. This means that even a vessel that passes a room-temperature hydrotest after service may develop catastrophic brittle fracture under subsequent thermal cycling.
- Loss of creep resistance. The graphite-occupied grain boundaries can no longer slide harmlessly, concentrating stress and accelerating tertiary creep.
Why 201 Solves This
At 0.02% maximum carbon, the total mass of carbon available for graphite precipitation in Nickel 201 is about 7.5× lower than the worst-case Nickel 200. More importantly:
- At 0.02% C (200 ppm carbon), the equilibrium volume fraction of graphite at 550 °C is approximately 0.15 volume percent — well below the threshold at which grain boundary continuity is established.
- At 0.15% C (1,500 ppm carbon), the equilibrium graphite fraction is about 1.1 volume percent — enough to form a near-continuous graphite film along austenite grain boundaries.
This is not a gradual degradation. It is a percolation threshold effect: once graphite forms a connected network at grain boundaries, the mechanical properties collapse rapidly. Nickel 201 lives safely below this threshold; Nickel 200 does not.
Practical Time-Temperature-Exposure Relationship
| Service Temperature | Nickel 200 — Time to Embrittlement | Nickel 201 — Embrittlement Risk |
|---|---|---|
| < 315 °C | Indefinite (safe) | Indefinite (safe) |
| 315–425 °C | 5,000–20,000 hr | Indefinite (safe) |
| 425–550 °C | 500–2,000 hr | Indefinite (safe) |
| 550–650 °C | 100–500 hr | >100,000 hr (safe) |
| > 650 °C | Carbon re-dissolves; short-duration exposure acceptable; risk on re-heating through 425–650 °C zone | Safe (carbon remains in solution) |
This table is the essence of the Nickel 200 vs 201 decision. For service temperatures above 315 °C — a conservative threshold that leaves safety margin — specify Nickel 201, not 200. No exceptions, no waivers.
3. Mechanical Properties
In the annealed condition, the mechanical properties of Nickel 200 and 201 are essentially identical. This is expected: with 99%+ Ni content and no deliberate alloying, the strength is controlled by grain size (Hall-Petch effect) rather than by the tiny carbon difference.
| Property | Nickel 200 | Nickel 201 | Note |
|---|---|---|---|
| Density (g/cm³) | 8.89 | 8.89 | Identical |
| Melting point (°C) | 1,435–1,446 | 1,435–1,446 | Identical |
| UTS (MPa, annealed) | 380–550 | 350–480 | 200 slightly higher (carbon effect) |
| 0.2% YS (MPa, annealed) | 100–210 | 80–180 | 200 slightly higher |
| Elongation (%) | 40–55 | 40–55 | Comparable |
| Hardness (HRB, annealed) | 45–70 | 45–65 | 200 marginally harder |
| Modulus (GPa) | 204 | 204 | Identical |
| Poisson’s ratio | 0.31 | 0.31 | Identical |
| Thermal conductivity (W/m·K, at 20 °C) | 70 | 70–79 | 201 slightly higher (less carbon scatter) |
| CTE (μm/m·°C, 20–100 °C) | 13.3 | 13.3 | Identical |
Elevated-Temperature Strength
At elevated temperatures, the carbon in Nickel 200 provides a slight strengthening effect (interstitial solid-solution hardening). This means that at 300–400 °C, Nickel 200 is marginally stronger than 201. However, this strength advantage is meaningless if the material is simultaneously undergoing graphite embrittlement, so Nickel 201 is specified for all elevated-temperature service regardless.
Ductile-to-Brittle Transition
A key advantage of pure nickel over most engineering alloys: neither Nickel 200 nor 201 exhibits a ductile-to-brittle transition. Both remain fully ductile down to −196 °C (liquid nitrogen) and below, with Charpy impact values actually increasing at cryogenic temperatures. This makes pure nickel uniquely suitable for cryogenic hydrogen service vessels and liquid oxygen piping.
ASME Boiler and Pressure Vessel Code
Both grades are approved for ASME Section VIII Division 1 construction under ASTM B162 specification for plate/sheet. For pressure vessel design, the ASME allowable stresses are published in Section II Part D:
- Nickel 200 (SB-162): Allowable stress 70–80 MPa (annealed) at room temperature, declining to 20–30 MPa at 500 °C. The code limits maximum service temperature to 315 °C for Nickel 200 — a direct reflection of the graphite embrittlement concern.
- Nickel 201 (SB-162): Similar room-temperature allowable stress. Maximum code-permitted temperature: 650 °C, reflecting the absence of appreciable graphite precipitation.
This code temperature ceiling reflects the difference between “safe indefinitely” and “at risk of embrittlement.”
4. Corrosion Resistance
In most corrosive environments, Nickel 200 and 201 perform identically. Corrosion resistance in pure nickel is governed by the nickel matrix itself, not by μ-constituents. The 0.13% carbon difference is negligible in the electrochemical sense. However, one environment deserves specific attention: anhydrous hydrogen fluoride (AHF).
Caustic Soda (NaOH)
Pure nickel is the material of choice for caustic soda service across the full concentration and temperature range. Its resistance to NaOH at concentrations up to 75% and temperatures to 400 °C (for 201) is essentially unmatched among common engineering metals. Corrosion rates are typically below 0.005 mm/year (0.2 mpy) — negligible.
The exception is NaOH containing oxidizing impurities such as chlorates (ClO₃⁻) or hypochlorites (ClO⁻), which can cause stress-corrosion cracking in pure nickel. In oxidizing caustic, step up to Inconel 600 or Incoloy 825, which are immune to caustic SCC.
Anhydrous HF (AHF)
Pure nickel is the reference material for anhydrous HF service at temperatures up to approximately 230 °C. Corrosion rates in dry HF are below 0.025 mm/year. The carbon content does not affect AHF resistance, so both Nickel 200 and 201 are suitable, and the choice is dictated by temperature: 200 for ambient-to-moderate AHF, 201 for elevated-temperature AHF.
For HF containing water (>1%), the Monel 400 family is preferred because its copper content buffers the depolarizing effect of aqueous HF. See our Monel K-500 vs 400 comparison for guidance.
Hydrogen Service (H₂)
Nickel 200 and 201 are widely used for high-temperature hydrogen piping and reactor components in hydrocarbon cracking and ammonia synthesis. Hydrogen embrittlement is not a concern at the carbon levels present in either grade, but the graphite embrittlement mechanism in Nickel 200 above 315 °C imposes the same 201-only rule.
Sulfidic Environments
Pure nickel is susceptible to sulfidation above approximately 350 °C and to sulfur embrittlement (formation of low-melting Ni₃S₂-Ni eutectic at 645 °C) in H₂S-containing environments. This is true for both Nickel 200 and 201. For sulfidic service, step up to a chromium-containing nickel alloy such as Inconel 600 or Hastelloy C-276, which develop a protective Cr₂O₃ scale.
General Acid and Chloride Resistance
| Environment | Nickel 200/201 | Notes |
|---|---|---|
| HCl (any concentration) | ❌ | Attack in both oxidizing and reducing |
| H₂SO₄ (dilute, non-oxidizing) | ✅ at low temp | Good in deaerated H₂SO₄ up to 40 °C |
| H₂SO₄ (concentrated, >80%) | ⚠️ | Marginal; Monel 400 preferred |
| HNO₃ (all concentrations) | ❌ | Rapid attack (oxidizing) |
| H₃PO₄ (pure, non-oxidizing) | ✅ | Acceptable at moderate temperatures |
| Seawater / neutral chlorides | ✅ | Excellent; no pitting or crevice |
| HF (anhydrous) | ✅ | Reference material, to ~230 °C |
| HF (aqueous) | ⚠️ | Monel 400 preferred |
| Alkalis (NaOH, KOH) | ✅ | Exceptional; reference material |
For a deeper dive into how pure nickel fits into the broader corrosion-ranking landscape, see our corrosion resistance comparison guide.
5. High-Temperature Applications — Where Nickel 201 Dominates
Caustic Evaporators and Concentrators
The single largest application for Nickel 201 is caustic soda (NaOH) evaporator tubes, shells, and tube sheets. In the chlor-alkali industry, NaOH from the diaphragm- or membrane-cell process is concentrated from approximately 32% to 50% or 73% in multi-effect evaporators operating at 150–400 °C. Nickel 201 tube bundles in these evaporators routinely achieve service lives of 20–30 years because the combination of caustic resistance and absence of graphite embrittlement makes it uniquely durable.
Nickel 200 would suffer graphite embrittlement in the hotter effects (last-stage evaporators running at 350–400 °C), with documented failures in as little as 2,000–5,000 hours of service.
Anhydrous Hydrofluoric Acid (AHF) Vessels and Piping
Pure nickel vessels (B162 plate, rolled and welded) are the industry standard for AHF storage above 150 °C, where carbon-steel linings fail and Monel 400 becomes marginal. Nickel 201 is specified for AHF reactor shells and piping operating at 180–230 °C. Nickel 200 is adequate for ambient-temperature AHF storage.
High-Temperature Hydrogen Service
In ammonia synthesis loops, hydrocarbon steam-methane reforming (SMR) effluent coolers, and nuclear isotope separation (heavy water concentration in the Girdler sulfide process), pure nickel piping must resist both high-temperature hydrogen attack and carbon-related embrittlement. Nickel 201 is the standard grade for these services up to 650 °C. Nickel 200 would fail by graphite embrittlement within months.
Hydrocarbon Cracking — Ethylene Furnace Transfer Line Exchangers
Ethylene furnace TLEs (Transfer Line Exchangers) operate with tube-skin temperatures of 350–600 °C on the process side. Nickel 201 is specified for the tube sheet cladding and tubes in units processing feed with high sulfur and low coke. The absence of graphite embrittlement at these intermediate temperatures is the key selection driver — Inconel 600 or 800HT would also survive thermally, but at higher cost and with some sulfidation risk.
Thermal Decomposition of NH₃ and H₂ Recycle
Ammonia dissociation units (for producing cracked ammonia for nitriding atmospheres) and hydrogen recycle compressors in refineries operate with pure or mixed H₂/N₂ at 400–550 °C. Nickel 201 is the preferred material for the hot-section piping, heater tubes, and catalyst supports because it does not catalyze unwanted side reactions (unlike Fe-based alloys) and does not embrittle from carbon/graphite precipitation.
6. Applications Where Nickel 200 Is the Right Choice
If your service temperature stays below 315 °C, Nickel 200 is often the more cost-effective and more available grade. The following are classic Nickel 200 applications:
Food Processing Equipment
Nickel 200’s bright, passive surface is non-toxic, easily cleaned, and FDA-compliant for direct food contact. It is used for chocolate tanks, dairy heat exchangers, and syrup evaporators where corrosion resistance is adequate (mild organic acids) and metallic contamination must be avoided.
Synthetic Fiber Production
Viscose rayon spinnerets, filament extrusion dies, and heat-setting rollers in the synthetic fiber industry demand a combination of corrosion resistance to organic spinning acids, dimensional stability, and a fine-polishable surface. Nickel 200 is the standard material for these components.
Electronics and Battery Components
Nickel 200 strip and foil are used for lithium-ion battery tab stock, primary alkaline battery collectors, semiconductor lead frames, and magnetostrictive devices. The low carbon content of Nickel 201 offers no advantage in these near-ambient-temperature applications, and the slightly higher strength of Nickel 200 is preferred.
Ambient-Temperature Alkali Handling
NaOH, KOH, and K₂CO₃ handling at temperatures below 100 °C — piping, storage tanks, pump impellers, and valves — can use Nickel 200 without risk of graphite precipitation. The cost savings vs. 201 are modest (typically 5–10% price difference), but availability is significantly better for 200.
Laboratory and Analytical Equipment
Pure nickel crucibles, combustion boats (for carbon/sulfur analysis by combustion infrared detection), and electroplating basket anodes are typically fabricated from Nickel 200 because service temperatures are below 315 °C and low carbon offers no benefit.
7. Fabrication and Welding
Forming
Both grades are highly ductile in the annealed condition and can be formed by all common methods: bending, deep drawing, spinning, and hydroforming. Nickel 200 is slightly more formable because its lower annealed strength permits more deformation per pass, but the difference is marginal in practice.
Work-hardening rates are similar — roughly comparable to Type 304 stainless steel, with a tensile-strength-to-yield ratio that climbs from approximately 2.5 in the annealed condition to 1.1–1.2 after heavy cold work.
Machining
Nickel 200 and 201 are gummy in the annealed condition and readily work-harden under the tool. Machining recommendations:
- Use carbide tooling with positive rake angles and sharp edges.
- Feed rates should be aggressive enough to keep the tool cutting below the work-hardened layer (typically 0.25–0.50 mm/rev).
- Heavy sulfurized or chlorinated cutting fluids are beneficial.
- Stress-relief anneal (650–750 °C, 30–60 min) before finish machining removes residual stresses that would cause distortion.
Welding
Both grades are readily weldable by all common processes. The carbon difference has minimal effect on welding performance because the short thermal cycle of welding does not provide sufficient time for graphite precipitation in Nickel 200 weld metal.
| Process | Nickel 200 | Nickel 201 | Filler Recommendation |
|---|---|---|---|
| GTAW (TIG) | ✅ Excellent | ✅ Excellent | ERNi-1 (ENi-1) |
| GMAW (MIG) | ✅ Good | ✅ Good | ERNi-1 (ENi-1) |
| SMAW (Stick) | ✅ Good | ✅ Good | ENi-1 electrodes |
| SAW | ✅ Good | ✅ Good | ERNi-1 wire + neutral flux |
| Resistance welding | ✅ Good | ✅ Good | No filler needed |
Filler metal: ERNi-1 (ENi-1) — a nominally matching composition with ≥ 93% Ni, ≤ 0.15% C, ≤ 1.0% Fe — is the standard filler for both grades. The filler metal carbon content is higher than the Nickel 201 base metal, but the volumetric dilution of the filler in the weld deposit is low enough that the average weld-metal carbon remains below the embrittlement threshold for moderate-temperature service.
For the most severe elevated-temperature welds in Nickel 201 (above 500 °C), a low-carbon ERNiCu-7 (Monel 400 filler) or ERNiCr-3 (Inconel 600 filler) is sometimes specified to provide a stronger, more creep-resistant weld deposit, but this is rarely necessary.
For a broader guide on nickel-alloy welding practices, see our welding nickel alloys article.
8. Cost and Availability
| Factor | Nickel 200 | Nickel 201 |
|---|---|---|
| Price premium vs 200 | — | 5–10% |
| Plate/sheet availability | Excellent | Good |
| Pipe and fittings | Excellent | Moderate (longer lead) |
| Bar and forging stock | Excellent | Good |
| Mill sources | Multiple global mills | Fewer mills; verify 0.02% C compliance |
| Lead time | 2–6 weeks (ex-stock common) | 4–12 weeks |
The price difference is driven primarily by the more controlled melting practice required to hit 0.02% C consistently (vacuum remelting or tight AOD/VOD control), not by the raw material cost. In small quantities, the premium can be 15–20% if a low-carbon heat must be sourced on expedite; in large contract volumes, the difference narrows to 3–8%.
Verification of Carbon Content
When specifying Nickel 201, the most common supply-chain failure mode is receiving material that meets the 99.0% Ni requirement but does not meet the 0.02% C ceiling — essentially, Nickel 200 sold as 201. Mill test certificates (MTCs) should be reviewed before acceptance, and a positive material identification (PMI) check with an optical emission spectrometer capable of carbon analysis (not just a handheld XRF, which cannot detect carbon) is recommended for critical elevated-temperature service.
9. Selection Decision Guide
| Service Condition | Recommended Grade | Rationale |
|---|---|---|
| T < 315 °C, any environment | Nickel 200 | Carbon embrittlement does not occur below 315 °C; 200 is more available and slightly cheaper |
| T = 315–425 °C (e.g., moderate-temp caustic) | Nickel 201 | 200 embrittles in 5,000–20,000 hr |
| T = 425–550 °C (e.g., AHF reactor, hot caustic) | Nickel 201 | 200 embrittles in 500–2,000 hr |
| T = 550–650 °C (e.g., ammonia cracker, TLE) | Nickel 201 | 200 fails in 100–500 hr |
| Cryogenic (< −100 °C) | Nickel 200 | Both ductile; 200 slightly more available |
| Food processing | Nickel 200 | Service temperatures well below 315 °C |
| NaOH < 100 °C | Nickel 200 | Adequate at ambient temperature |
| NaOH evaporator ≥ 150 °C | Nickel 201 | Specified for 20–30 yr service life |
| Anhydrous HF < 150 °C | Nickel 200 | Adequate carbon-wise; cost-effective |
| Anhydrous HF 150–230 °C | Nickel 201 | Carbon control essential |
| Hydrogen service > 315 °C | Nickel 201 | Irreversible if 200 is specified |
| ASME VIII vessel > 315 °C | Nickel 201 | Code compliance; 200 is code-limited to 315 °C |
When 200 Is Entirely Adequate
Approximately 60–70% of pure nickel applications in industry are at service temperatures below 250 °C — ambient-pressure chemical tanks, ambient-temperature alkali handling, electroplating equipment, food processing, and electronics. In these applications, Nickel 200 is the correct, cost-effective specification, and specifying 201 adds unnecessary cost and lead time.
When 201 Is Non-Negotiable
Any application with sustained metal temperatures above 315 °C — caustic evaporators, AHF reactors above 150 °C, hydrogen recycle piping, ammonia crackers, and ASME VIII vessels designed for elevated-temperature service — must use Nickel 201. There is no metallurgical countermeasure (no heat treatment, no process control, no post-weld treatment) that renders Nickel 200 safe for service above 315 °C. The carbon precipitates irreversibly, and the only corrective action is replacement.
FAQ
Q1: Can I use Nickel 200 for a vessel that will see short-term excursions above 315 °C, such as a steam-out or process upset?
Short-term excursions on the order of a few hours — such as an 8-hour steam-out of a process vessel at 350 °C pipe-wall temperature — are generally not sufficient to cause graphite embrittlement in Nickel 200. However, any sustained operation above 315 °C for more than approximately 100–200 cumulative hours should trigger a switch to Nickel 201. The ASME code position is clear: Nickel 200 is not permitted for pressure-containment service above 315 °C. If your vessel is code-stamped, steam-out temperature is considered a design-case temperature and must stay within code limits.
Q2: Is Nickel 201 always more expensive than Nickel 200?
Yes, typically 5–10% more on a per-kilogram basis in plate form, and slightly more in small mill quantities. However, if you are buying only a few hundred kilograms, the availability premium can push the difference to 15–20%. The cost premium is entirely from the more controlled melting practice, not from higher raw-material cost.
Q3: Can I weld Nickel 201 tubes to a Nickel 200 tube sheet?
Yes, with the standard ERNi-1 filler metal. The weld deposit carbon content will be intermediate between the two base metals (the filler’s ≤0.15% C is diluted by the base metals), and for service temperatures up to approximately 400 °C, the weld remains well below the embrittlement threshold. For tube-sheet welds in caustic evaporators operating above 450 °C, specify Nickel 201 for the tube sheet as well, to avoid any risk of embrittlement in the heat-affected zone (HAZ) of the parent metal.
Q4: Do I need to solution-anneal Nickel 201 after welding to prevent graphite embrittlement?
No, not for the base metal’s graphite embrittlement resistance. Graphite precipitation is a time-at-temperature phenomenon that occurs during service, not during welding. Post-weld heat treatment (PWHT) at 700–850 °C followed by rapid cooling is sometimes applied to stress-relieve weldments in thick sections (>25 mm) for caustic service, but the goal is to prevent caustic stress-corrosion cracking (SCC), not to prevent graphite precipitation. The graphite embrittlement protection in Nickel 201 comes from the chemistry — 0.02% C max — and does not require or benefit from PWHT.
Q5: What is the practical difference between “Nickel 200” and “Nickel 201” in terms of supply-chain risk?
Two supply-chain risks deserve attention:
- Documentation mismatch: Nickel 201 is sometimes certified as meeting Nickel 200 requirements (since 201 is a subset of 200 chemistry) but not vice versa. Always verify that the grade on the MTC matches what you ordered — not just that it “meets the chemistry.”
- Carbon analysis: A handheld XRF gun cannot detect carbon. If your receiving inspection relies solely on XRF for positive material identification, you cannot verify the 0.02% C limit. For critical elevated-temperature Nickel 201 service, require carbon analysis on the mill certificate and, if the application justifies it, a third-party check analysis on a representative sample using combustion infrared detection (ASTM E1019 or equivalent).
Summary
Nickel 200 and 201 are essentially the same material with one critical difference: the carbon ceiling, which controls graphite embrittlement above 315 °C.
- Below 315 °C: Use Nickel 200. It is more widely available, slightly cheaper, and marginally stronger. The 0.15% C maximum is harmless below the graphite precipitation range. This covers food processing, ambient-temperature chemical handling, electronics, electroplating, and synthetic fiber manufacturing — approximately 60–70% of all pure nickel applications.
- Above 315 °C: Specify Nickel 201. Period. No exceptions. The carbon precipitates irreversibly as graphite at grain boundaries, causing a ductile-to-brittle transition that has been documented in thousands of failed Nickel 200 vessels and piping components worldwide. The ASME code forbids Nickel 200 pressure-containment use above 315 °C. The cost premium of 5–10% for Nickel 201 is a vanishingly small insurance premium against a catastrophic service failure that requires complete replacement, typically costing 100–200× the material-cost premium.
- In doubt? Specify 201. The price difference is small; the cost of being wrong is enormous. At the project-estimate stage, listing “Nickel 200 or 201” on a piping line class is ambiguous and invites substitution of the cheaper grade in a service where it will fail. Be explicit. Write “201” when the temperature justifies it, and verify the carbon limit on the MTC before the pipe is installed.
