Short Description
Product: 3.5% Nickel Low-Temperature Seamless Steel Tube – ASTM A334 Grade 3 (UNS K12021 / 3.5Ni), cold drawn, normalized and air cooled for seamless and welded carbon and alloy steel tubes intended for use at low temperatures.
Product Short Description: Womic Steel Group has established mature, mass-production capabilities for small diameter, extra-long 3.5Ni seamless tubes – covering 25mm OD x 2mm WT x 22m individual length – fully meeting ASTM A334 Grade 3 low-temperature toughness requirements down to -101°C. This production line addresses the historical reliance on imports for small-diameter, extra-long 3.5Ni tubes. The 3.5% nickel steel provides excellent notch toughness and ductility at temperatures as low as -150°F (-101°C), making it a critical material for LNG terminals, ethylene cracker units, air separation plants, and polar projects.
Outside diameter from 10mm to 610mm (hot-rolled), wall thickness from 1.5mm to 25.4mm, single lengths up to 24m. Cold drawn precision OD range: 6mm to 89mm, with tight dimensional tolerances as low as ±0.10mm.
Contains approximately 3.5% nickel, with a low-carbon, high-nickel composition to significantly enhance low-temperature toughness and prevent low-temperature embrittlement at -101°C. Typical composition: C ≤0.19%, Mn 0.31-0.64%, Si 0.18-0.37%, Ni 3.18-3.82%, P ≤0.025%, S ≤0.025%.
3.5Ni (ASTM A334 Grade 3) is positioned between standard low-temperature steel Grade 6 (-45°C) and high-end 9% Ni steel Grade 8 (-196°C). It serves as the most cost-effective solution for the -50°C to -101°C service range.
Complies with ASTM A334/A334M, ASME SA334, ASTM A333/A333M Grade 3, as well as ASTM/ASME, PED, and NACE MR0175 (upon request).
LNG receiving terminals auxiliary piping, PDH (Propane Dehydrogenation) units, ethylene crackers, air separation units, and offshore platform piping systems for polar regions.
Womic Steel Group is a specialized manufacturer and global exporter of low-temperature seamless tubes, small-diameter precision pipes, and extra-long seamless tubes. With over 20 years of cold-drawing expertise, our 3.5Ni seamless tubes for -101°C service are now available for bulk orders. Mill certificates, 100% ultrasonic and hydrostatic testing, positive material identification, and full dimensional inspection reports with single-heat traceability are provided. Third-party inspection (SGS/BV/DNV/TÜV) accepted. Competitive pricing and fast delivery.
Section 1: Background – Why 3.5Ni Seamless Tubes at -101°C?
Since the 1930s, when the United States first developed 3.5% nickel steel for low-temperature service (eventually standardized under ASTM A334/A334M and A333/A333M), Europe and Japan have also developed their own 3.5Ni steel grades. These materials have widely served ethylene crackers, LPG/LNG transport, fertilizer plants, rubber processing, and coal gasification industries.
3.5Ni steel is a low-carbon, high-nickel low-alloy steel with a nickel (Ni) content of approximately 3.5%. Through normalizing or normalizing and tempering heat treatment, it provides a stable ferrite + bainite microstructure and excellent low-temperature impact toughness. It is a well-established, internationally recognized material used for pressure vessels and piping systems in -101°C low-temperature environments.
In China, 3.5Ni steel plate and forgings have achieved mature, reliable industrial production for many years, demonstrating excellent technical performance and cost effectiveness. However, seamless tubes — particularly small-diameter, extra-long 3.5Ni tubes — have remained in limited supply.
To fill this industry gap, Womic Steel has established a dedicated production line leveraging its core competencies in low-temperature seamless tube manufacturing, small-diameter precision production, and extra-long tube cold-drawing technology. After systematic process development and multi-batch validation, our 25mm OD x 2mm WT x 22m extra-long 3.5Ni seamless tubes entered mass production, with the first batch delivered in April to a major domestic equipment manufacturer. The tubes will be used in a Russian Arctic Circle project.
Nationally accredited testing confirmed that all key performance indicators – including -101°C low-temperature Charpy impact toughness, room-temperature tensile properties, dimensional accuracy, and surface finish – fully meet ASTM A334 Grade 3 requirements and are fully comparable to internationally advanced levels.
Section 2: Comparative Grade Analysis – Selecting the Right Low-Temperature Steel
High-alloy steel seamless pipes for low-temperature environments mainly include ASTM A333/A334 Grades 3, 4, 6, 7, 8, 9, and 11. Among them, Grades 3, 4, 7, and 8 are the most commonly specified for medium and severe low-temperature service. Selecting the appropriate material depends on the required minimum service temperature, design pressure, and budget.
The following table provides a comprehensive comparison of the primary low-temperature steel grades, including their applicable temperature ratings, mechanical properties (tensile and yield strength), and key applications. This comparison will help clarify the market position of 3.5Ni steel (ASTM A334 Grade 3) relative to alternative materials.
Table: ASTM A333/A334 Low-Temperature Steel Grade Comparison
| Grade Designation | Min Service Temp | Ni Content | Tensile Strength (min) | Yield Strength (min) | Elongation | Type & Key Applications |
|---|---|---|---|---|---|---|
| Grade 6 | -45°C (-50°F) | ≤0.5% | ≥415 MPa | ≥240 MPa | ≥30% | Low-Carbon Manganese Steel. Most common & economical grade. Water treatment, general refrigeration, cold climate pipelines. |
| Grade 3 (3.5Ni) | -101°C (-150°F) | 3.18-3.82% | ≥450 MPa | ≥240 MPa | ≥30% (L) / ≥20% (T) | 3.5% Nickel Steel. Cost-effective for -50°C to -101°C range. PDH units, ethylene plants, air separation units, Arctic pipelines. |
| Grade 4 | -101°C (-150°F) | ≤0.5% | ≥415 MPa | ≥240 MPa | ≥30% | Killed Carbon Steel. Matrix structure containing a small amount of ferrite. Limited low-temperature toughness compared to 3.5Ni. |
| Grade 7 | -73°C (-100°F) | 2.0-2.5% | ≥450 MPa | ≥240 MPa | ≥30% | 2.5% Nickel Steel. Intermediate option between Grade 6 and Grade 3. |
| Grade 8 (9Ni) | -196°C (-320°F) | 8.4-9.6% | ≥690 MPa | ≥515 MPa | ≥22% | 9% Nickel Steel. Excellent extreme low-temperature toughness. LNG main piping (-162°C). |
| Grade 11 (High Toughness) | -196°C. Similar to Gr.8 | Similar to Gr.8 | Similar to Gr.8 | Similar to Gr.8 | Similar to Gr.8 | Forged from high-quality killed steel, utilized for critical ultra-low-temperature components. |
Section 3: Chemical Composition – Stringent Control for ASTM A334 Grade 3 Conformity
Drawing on mature, proven experience with 3.5Ni steel plate and hot-rolled seamless tubes production, Womic Steel has established tightly controlled chemical composition ranges specifically for the cold-drawn small-diameter tube process. This ensures superior low-temperature toughness while maintaining stable cold-drawing manufacturability.
| Element | ASTM A334 Gr.3 (Max/Req’d) | Womic Steel Design Target | Womic Steel Actual Ladle Analysis |
|---|---|---|---|
| Carbon (C) | ≤0.19% | 0.06 – 0.09% | 0.07% |
| Silicon (Si) | 0.18 – 0.37% | 0.18 – 0.33% | 0.24% |
| Manganese (Mn) | 0.31 – 0.64% | 0.45 – 0.60% | 0.51% |
| Phosphorus (P) | ≤0.025% | ≤0.010% | 0.004% |
| Sulfur (S) | ≤0.025% | ≤0.005% | 0.001% |
| Nickel (Ni) | 3.18 – 3.82% | 3.30 – 3.70% | 3.40% |
*The combination of low carbon content (C ≤0.19%), ultra-low phosphorus and sulfur (P ≤0.025%, S ≤0.025%), and precise 3.18-3.82% nickel addition eliminates the risk of low-temperature embrittlement at -101°C, while meeting ASTM A334 Gr.3 chemical and mechanical requirements and ensuring excellent cold workability during the drawing process.*
Section 4: Mechanical Properties – Validated ASTM A334 Grade 3 Compliance
Mechanical properties were tested on both the mother tube (full wall thickness) and the finished tube (surface) after identical heat treatment, with samples taken from the regular production batch.
Room Temperature Tensile Properties
| Property | ASTM A334 Gr.3 Requirement | Womic Steel Actual (Regular Production) |
|---|---|---|
| Yield Strength (0.2% offset) | ≥240 MPa | 330 – 360 MPa |
| Tensile Strength | ≥450 MPa | 520 – 550 MPa |
| Elongation (longitudinal) | ≥30% | 32 – 36% |
| Elongation (transverse) | ≥20% | 26 – 30% |
| Hardness (HB) | ≤190 | 160 – 175 |
Metallographic Structure
After normalizing heat treatment at ≥845°C followed by air cooling, the finished tube exhibited a fine ferrite + bainite microstructure with a grain size rating of approximately ASTM No. 10 (highly refined grain), which contributes to superior low-temperature toughness.
-101°C Low Temperature Charpy Impact Toughness
Because direct impact testing of the finished thin-wall tube (25x2mm) is not possible per standard practices (specimen too small), Womic Steel took mother tube samples of the same heat number, subjected them to the identical normalized heat treatment as the finished tubes, and then machined them into sub-size 2.5x10x55mm Charpy V-notch specimens. Impact testing was then conducted at an even lower temperature of -117°C, exceeding the -101°C design requirement, to demonstrate an ample safety margin.
| Test Temperature | Sample 1 | Sample 2 | Sample 3 | ASTM Requirement (2.5mm subsize) |
|---|---|---|---|---|
| -117°C | 32J | 33J | 35J | Min average ≥5J; single ≥4J |
The impact test results far exceed ASTM minimum requirements, demonstrating the material’s exceptional low-temperature toughness with a substantial safety margin beyond the rated -101°C service temperature.
Section 5: Manufacturing Process – Mature Cold Drawing and Heat Treatment for Small Diameter Extra-Long Tubes
Womic Steel produces 3.5Ni low-temperature seamless tubes using a fully industrialized manufacturing route specifically optimized for small-diameter, extra-long, high surface finish products:
- Electric Arc Furnace Melting + Ladle Refining + Vacuum Degassing: Ensures extremely low hydrogen, oxygen, and nitrogen contents, as well as tight chemistry control (P ≤0.005%, S ≤0.001%).
- Continuous Casting + Bloom Rolling: Produces high surface quality tube hollows with fine internal soundness.
- Hot Piercing (Cross Roll Piercing): Billets are heated in a walking beam furnace and pierced into heavy wall hollow shells at optimized rolling temperatures; eccentricity is minimized.
- Cold Pilgering / Cold Drawing – Multiple passes (with intermediate annealing): This is the key process for achieving ultra-long tubes. For the 25x2mm final size, the process typically requires three precisely controlled cold drawing passes, with each pass work-hardening the material. Between passes, the tubes undergo intermediate annealing to restore ductility and prevent work hardening cracks.
- Solution Annealing (Normalizing): Carried out in a controlled atmosphere furnace at ≥845°C, followed by air cooling to relieve cold working stresses and refine the microstructure.
- Straightening: Precision roller straightening ensures straightness tolerance of ≤1.5mm per meter.
- Cutting to Length and End Finishing: Flying cutoff saws achieve high precision; ends are deburred or beveled as required.
- 100% NDT, Hydrostatic Testing, and Marking: Each tube is ultrasonically tested, eddy current tested, and pressure tested before final low stress stamping.
- Final dimension achieved: 24.96 – 25.05mm OD × 2.04 – 2.16mm WT × 22m length. ID and OD surface roughness ≤1.4μm Ra, meeting Grade 1 heat exchanger tube quality per NB/T 47019.1-2021 (sub micrometer surface finish).
Section 6: Quality Control and Testing – Comprehensive Performance Verification
Every production batch of 3.5Ni low temperature seamless tubes is tested according to ASTM A334/A334M:2021 standards.
Certificates: Mill Test Certificate per EN 10204 Type 3.1. Type 3.2 with third party witness (SGS/BV/DNV/TÜV) is available upon request.
Batch-to-batch consistency: Womic Steel maintains detailed records for each heat number and each batch, ensuring full traceability of every finished tube.
Section 7: Applications – Where 3.5Ni ASTM A334 Grade 3 Tubes Excel
3.5Ni low-temperature seamless tubes are designed for reliable long-term operation in the -45°C to -101°C service range, filling the gap between standard Grade 6 material and high-cost 9% Ni Grade 8 material.
The 3.5Ni tube serves as the most cost-effective material choice for the temperature range between -50°C (Grade 6) and -196°C (9% Ni Grade 8), making it the preferred solution for the majority of petrochemical low-temperature applications.
Section 8: Why Choose Womic Steel for 3.5Ni Low-Temperature Seamless Tubes?
Frequently Asked Questions (FAQ)
Contact Womic Steel
For inquiries, technical support, or to request a quotation for your specific 3.5Ni low temperature tube requirements under ASTM A334 Grade 3 (or other low temperature grades), please contact us directly.
Post time: Jun-24-2026