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BS T — Aerospace Seamless Steel Tubes Specifications Single-File Series Overview (3 Standards)
Covers seamless steel tubes at 1390, 1160 and 770 MPa strength grades (incl. 12% chromium corrosion-resisting steel)
📐 The BS T series is a group of specifications for seamless steel tubes within the UK Aerospace Series, prepared by BSI’s Aerospace Standards Committee. These specifications set chemical composition, heat treatment schedules, dimensional tolerances and mechanical property requirements for various alloy steel seamless tubes used in aerospace applications such as hydraulic systems, fuel lines, structural members and engine plumbing. This overview covers three BS T specifications at the 1390 MPa and 1160 MPa strength grades of Ni-Cr-Mo steel, together with a 12% chromium 770 MPa corrosion-resisting tube.
Aerospace tube specifications are normally used with associated purchasing, inspection and testing requirements, and each specification is often a conversion of a UK Ministry of Defence (DTD/MOD(PE)) specification. Note the heat-treatment and supply conditions specified (e.g. cold drawn and heat treated).
1. Standard List and System Framework
The three BS T specifications covered in this overview are listed below, all being aerospace series seamless steel tube material specifications.
| Reference | Title |
|---|---|
| BS T 78:1975 | Specification for 0.5% chromium-4% nickel-1% molybdenum steel tubes (1390 MPa) |
| BS T 79:1975 | Specification for 0.5% chromium-3% nickel-1% molybdenum steel tubes (1160 MPa) |
| BS T 80:1975 | Specification for 12% chromium steel corrosion-resisting tubes (770 MPa) |
2. Technical Content of Representative Standards
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BS T 78:1975 — 0.5% chromium-4% nickel-1% molybdenum steel tubes (1390 MPa)
This specification sets material requirements for high-strength nickel-chromium-molybdenum steel seamless tubes for aerospace use, replacing UK MoD specification DTD 1530. It requires tubes to be supplied cold drawn and heat treated (tempered at a suitable temperature as final heat treatment), and specifies the heat treatment of annealing, hardening (heating and quenching in oil) and tempering, together with chemical composition and mechanical properties. The approximate composition ranges are carbon 0.30–0.38%, silicon ≤0.30%, manganese 0.35–0.75%, chromium 0.35–0.70%, nickel 3.60–4.60%, molybdenum 1.00–1.50%, with phosphorus and sulphur limited to about 0.025%. Mechanical properties: a 0.2% proof stress requirement, a tensile strength around the 1560–1820 MPa grade (corresponding to the 1390 MPa grade) and elongation/hardness requirements. This material has high strength and is used for aircraft hydraulic systems and high-strength structural tubing.
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BS T 79:1975 — 0.5% chromium-3% nickel-1% molybdenum steel tubes (1160 MPa)
This specification sets material requirements for nickel-chromium-molybdenum steel seamless tubes for aerospace use, replacing UK MoD specification DTD 1230. It requires tubes to be supplied cold drawn and heat treated (tempered), and specifies annealing, hardening and tempering together with chemical composition and mechanical properties. The approximate composition ranges are carbon 0.26–0.34%, silicon ≤0.30%, manganese 0.35–0.75%, chromium 0.35–0.70%, nickel 2.60–3.60%, molybdenum 0.30–0.60%, with phosphorus and sulphur limited to about 0.030%. Mechanical properties: tensile strength corresponding to the 1160 MPa grade (about 1300–1500 MPa), with 0.2% proof stress and elongation requirements. This material has moderately high strength with good toughness and is widely used for aircraft fuel, oil and structural tubing.
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BS T 80:1975 — 12% chromium steel corrosion-resisting tubes (770 MPa)
This specification sets material requirements for 12% chromium martensitic corrosion-resisting steel seamless tubes for aerospace use, replacing UK MoD specification DTD 421. It requires tubes to be supplied cold drawn and heat treated, and specifies annealing, hardening (cooling in air or in a manner that avoids cracking) and tempering, together with chemical composition and mechanical properties. The approximate composition ranges are carbon 0.09–0.15%, silicon ≤0.30%, manganese ≤1.00%, chromium 11.50–13.50%, molybdenum ≤0.50% as required, with phosphorus and sulphur limited to about 0.030%. Mechanical properties: a 0.2% proof stress requirement, a tensile strength corresponding to the 770 MPa grade (about 850–1000 MPa), and elongation/hardness requirements. 12% chromium steel combines moderate strength with corrosion resistance, used for corrosion-resisting tubing in aircraft hydraulic and pneumatic systems.
3. Key Technical Points
The key technical points of the BS T series can be summarized as follows:
| Reference | Title |
|---|---|
| 化学成分 | Alloy content and impurity limits for Ni-Cr-Mo (0.5Cr-Ni-Mo) and 12% chromium corrosion-resisting steels |
| 热处理 | Annealing, hardening (oil quench/air cool) and tempering; supplied cold drawn and heat treated |
| 力学性能 | Strength grades 1390, 1160, 770 MPa with proof stress, elongation and hardness requirements |
| 供货状态 | Cold-drawn and finally-heat-treated supply condition with dimensional tolerances |
The three strength grades cover typical aircraft tubing needs: 1390 MPa for high-pressure hydraulic systems, 1160 MPa for fuel/oil lines, and the 770 MPa 12% chromium steel for systems requiring corrosion resistance. All are cold-drawn seamless tubes ensuring dimensional accuracy and surface quality.
4. Engineering Practice and Application
✈️ Hydraulic systems: the 1390 MPa high-strength tube of BS T 78 is used for high-pressure aircraft hydraulic lines, withstanding high pressure and fatigue loads.
🛢️ Fuel and oil: the 1160 MPa tube of BS T 79 is used for fuel, oil and coolant lines, balancing strength and workability.
🔧 Corrosion-resisting lines: the 12% chromium tube of BS T 80 is used for hydraulic and pneumatic corrosion-resisting lines, remaining reliable in humid and corrosive environments.
5. FAQ
Q: Q: How does the grade (e.g. 1390 MPa) relate to tensile strength?
A: A: A grade such as “1390 MPa” is the designation in UK material specifications based on the 0.2% proof stress (or a specified strength index), corresponding to a higher tensile strength range (e.g. about 1560–1820 MPa). Use the proof stress, tensile strength and elongation requirements tabulated in the specification.
A: A: A grade such as “1390 MPa” is the designation in UK material specifications based on the 0.2% proof stress (or a specified strength index), corresponding to a higher tensile strength range (e.g. about 1560–1820 MPa). Use the proof stress, tensile strength and elongation requirements tabulated in the specification.
Q: Q: Why is 12% chromium steel both “corrosion-resisting” and fairly strong?
A: A: 12% chromium steel is a martensitic stainless steel; quenching and tempering give a medium-high strength of the 770 MPa grade, while chromium provides better corrosion resistance than carbon steel, suiting humid or corrosive environments in hydraulic/pneumatic systems.
A: A: 12% chromium steel is a martensitic stainless steel; quenching and tempering give a medium-high strength of the 770 MPa grade, while chromium provides better corrosion resistance than carbon steel, suiting humid or corrosive environments in hydraulic/pneumatic systems.
Q: Q: Why are most aerospace tubes cold drawn?
A: A: Cold drawing gives precise dimensional tolerances, good surface quality and refined structure, meeting the stringent requirements of aircraft tubing for wall-thickness uniformity, fatigue performance and fluid sealing.
A: A: Cold drawing gives precise dimensional tolerances, good surface quality and refined structure, meeting the stringent requirements of aircraft tubing for wall-thickness uniformity, fatigue performance and fluid sealing.
Q: Q: How do these specifications relate to DTD specifications?
A: A: These BS T specifications were mostly converted from existing UK MoD (DTD/MOD(PE)) specifications (e.g. BS T 78 supersedes DTD 1530, BS T 79 supersedes DTD 1230, BS T 80 supersedes DTD 421), continuing the content and standardizing it in the UK Aerospace Series.
A: A: These BS T specifications were mostly converted from existing UK MoD (DTD/MOD(PE)) specifications (e.g. BS T 78 supersedes DTD 1530, BS T 79 supersedes DTD 1230, BS T 80 supersedes DTD 421), continuing the content and standardizing it in the UK Aerospace Series.
Q: Q: What should be noted when applying BS T tubes?
A: A: Note the supply condition (cold drawn and heat treated), the mechanical testing and non-destructive inspection required at acceptance, compatibility with fittings/connectors, and cleanliness and pressure-grade requirements in hydraulic systems; confirm against the current official BSI edition.
A: A: Note the supply condition (cold drawn and heat treated), the mechanical testing and non-destructive inspection required at acceptance, compatibility with fittings/connectors, and cleanliness and pressure-grade requirements in hydraulic systems; confirm against the current official BSI edition.