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Chenzhou, Hunan, China(423000）)
- 2025-9-29
- handaseal
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MP35N is a vacuum-remelted, age-hardenable nickel-cobalt-chromium-molybdenum superalloy engineered for ultra-high tensile strength, excellent corrosion and sulfide stress corrosion cracking (SSC) resistance, and outstanding fatigue life — commonly used for spring-energized seals in sour, subsea and other aggressive environments.
Contents
Introduction & quick summary
MP35N (UNS R30035) is an age-hardenable Ni-Co-Cr-Mo alloy produced by VIM/VAR practices to ensure cleanliness and reliability. It is commonly supplied as precision spring wire and strip for critical energizers used in oil & gas (including sour service), subsea, aerospace and medical applications. For engineering design always request mill certificates and suppliers’ diameter-by-temper mechanical tables. Materials — Cobalt-Nickel Alloys.
Core characteristics
Typical chemical composition
Typical composition ranges (use mill certificate for exact lot values):
| Element | Typical composition (wt.%) |
|---|---|
| Nickel (Ni) | ≈ 33–37% |
| Cobalt (Co) | ≈ 33–37% (balance) |
| Chromium (Cr) | ≈ 19–21% |
| Molybdenum (Mo) | ≈ 9–10.5% |
| Titanium (Ti) | Trace (vendor dependent) |
| Fe, C, Si, Mn, P, S | Residual / trace levels — verify on mill certificate |
Typical composition references: Carpenter, Elgiloy and major suppliers’ datasheets.
Key physical data
Typical physical & thermal properties — always confirm with supplier datasheet for the chosen temper/lot:
| Technical specification | MP35N (typical) |
|---|---|
| Density | 0.304 lb/in³ (≈ 8.42 g/cm³). |
| Modulus of Elasticity (E) | ≈ 33.8 × 10⁶ psi (≈ 233 GPa). |
| Modulus of Rigidity (G) | ≈ 12.1 × 10⁶ psi (≈ 83.4 GPa). |
| Coefficient of Thermal Expansion | ≈ 8.2 µin/in-°F (70–600 °F) (≈ 14.8 µm/m-°C). |
| Electrical Resistivity | ≈ 40–41 µΩ·in. |
| Thermal Conductivity | ≈ 78 Btu·in/(ft²·hr·°F) (≈ 11.2 W/m·K). |
| Min wire size (typical availability) | Precision drawn wire commonly available down to ≈ 0.005 in (0.127 mm); confirm with supplier. |
| Max recommended continuous service temp | Guidance commonly ≈ 600 °F (≈ 315 °C); verify by temper with supplier. |
Physical / thermal values referenced to major supplier datasheets.
Metallurgical behaviour & tempering
MP35N develops ultra-high strength through heavy cold work and ageing (work-hardening + age treatment). Mechanical properties (UTS/YS/hardness and relaxation) vary with percent cold reduction and ageing schedule — always design from the supplier’s diameter-by-temper tables and the mill certificate. Typical ultimate tensile values in fully strengthened tempers can reach ~260–300 ksi (1793–2068 MPa) depending on drawing and ageing.
Typical applications
Chemical processing & aggressive chloride media
MP35N is used for seals, small fasteners and energizers in chemical plants where SSC, crevice and pitting risks exist. Supplier datasheets document strong SCC resistance in such chemistries. Carpenter — MP35N overview.
Oil & gas (sour service, downhole)
MP35N is commonly selected for packer springs, connector springs and sealing energizers in H₂S-containing environments where SSC resistance and high fatigue strength are required; client/NACE qualification testing remains typical for critical downhole uses.
Subsea & marine
MP35N exhibits excellent crevice and stress corrosion resistance in seawater at many strength levels, making it suitable for wet connectors, rotary seal energizers and cyclicly loaded subsea hardware. Elgiloy — MP35N strip.
High-reliability springs (medical, aerospace)
Selected tempers of MP35N are used for medical and aerospace springs where long life, strength and controlled corrosion resistance are demanded.
Processing & manufacturing key points
Purchasing & certification
Always procure spring-grade MP35N (UNS R30035) with mill certificate and diameter-by-temper mechanical tables (UTS, YS, hardness). For sour service reference NACE MR0175 / ISO 15156 as required by the project.
Machining, forming & tooling
MP35N requires polished tooling and conservative bend radii to minimize tooling marks that reduce fatigue life. Electropolishing/passivation after forming improves corrosion fatigue. Verify supplier forming recommendations for wire diameter & temper.
Welding & joining
Welding can be qualified but is not routine for many fine spring forms; mechanical interlocks or micro-welds are common — qualify end-joins for fatigue and corrosion performance where used.
Forming into springs & spring types
Reminder: spring energizers are formed from wire or strip. MP35N spring wire is routinely formed into energizer geometries; confirm wire diameter & temper availability with your spring supplier.
Forming best practices
- Use polished tooling and smooth coiling to minimise surface defects.
- Maintain conservative bend radii (recommend ≥ 3× wire dia).
- Age per supplier guidance when required to reach final UTS/hardness.
- Qualify end joins (mechanical / laser / micro-weld) for fatigue & corrosion performance.
Alternatives & comparison
Quick comparison of common energizer materials (corrosion resistance vs typical tensile strength):
| Material | Corrosion resistance (summary) | Strength (typical UTS, ksi) |
|---|---|---|
| MP35N (UNS R30035) | Excellent SSC, crevice & pitting resistance; excellent for sour & seawater service. Carpenter. | ~260–300 ksi (work-hardened & aged) (typical top tempers). |
| Elgiloy (cobalt-nickel alloy) | Excellent SSC and fatigue resistance; widely used for spring energizers in sour service. Elgiloy. | ~220–280 ksi depending on temper (vendor data). |
| Inconel 625 | Very good general corrosion resistance; good chloride resistance though SSC behaviour depends on environment. Inconel 625. | ~120–200 ksi (work/hardened tempers vary). |
| Inconel 718 | Good corrosion resistance; chosen for elevated temperature strength and relaxation resistance (high-T springs). Inconel 718. | ~150–200+ ksi (depending on temper/age). |
| 17-7 PH (stainless) | Moderate corrosion resistance; not recommended for severe SSC / H₂S exposures. | ~100–180 ksi (depending on tempers); typical spring grade strengths lower than MP35N/Elgiloy. |
| 316L / 316 (stainless) | General corrosion resistance but poor for high SSC / sour service at high hardness; better for benign/mild environments. | ~70–120 ksi (typical spring wire tempers). |
Notes: strength ranges are indicative — use supplier diameter/temper tables for exact UTS values and lot certification. Authoritative datasheets used for table content.
Selection guidance
Step 1 — Rank failure modes and constraints
- Presence of H₂S / Sulfide Stress Cracking (SSC) risk
- Corrosion type: pitting / crevice / uniform / sulfide
- Cyclic loading and required fatigue life (high-cycle vs low-cycle)
- Operating temperature and relaxation/creep requirements
- Geometry constraints (wire diameter availability) and required certifications
Step 2 — Quick decision rules
- MP35N: choose when SSC / H₂S risk and very high fatigue/strength are both critical (oil & gas, subsea).
- Elgiloy: when SSC resistance and superior forming for multi-contact energizers are required and cobalt alloys are acceptable.
- Inconel 625: when broad corrosion resistance and weldability are priorities and SSC risk is moderate/controlled.
- Inconel 718: for high-temperature springs where relaxation resistance matters.
- 17-7 PH / 316L: when cost and manufacturability are prioritized and SSC risk is low.
Always verify final selection with mill certificates, supplier diameter/temper mechanical tables and representative performance testing (force-deflection, high-cycle fatigue, stress-relaxation and relevant corrosion tests).
FAQ
Q1: Is MP35N suitable for sour (H₂S) downhole service?
A1: Yes — MP35N is widely used in sour service for its SSC resistance, but critical downhole applications normally require client or NACE/ISO qualification and explicit hardness/strength limits.
Q2: What spring types can be made from MP35N?
A2: MP35N spring wire and strip can be formed into canted coil, helical and garter springs — check wire diameter & temper availability with your spring vendor: Canted Coil, Helical.
Q3: What supplier data should designers request?
A3: Request mill certificate (UNS R30035), diameter-by-temper UTS/YS/hardness tables, expected relaxation % at operating temperature, and representative corrosion test data for the intended environment.
Q4: How to maximise MP35N spring life in corrosive service?
A4: Use polished tooling, conservative bend radii, remove tooling marks, electropolish/passivate, qualify end-joins and perform representative fatigue and stress-relaxation tests on assembled energizers.