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Hollow Bars
Hollow Bars
Hollow Bars｜Global Sourcing for Engineering & Procurement
1. Product Positioning & Scope
• Definition: Hollow bar is a thick-wall, hollow long product for machining. It focuses on machining allowance, concentricity, and straightness, and is typically supplied to EN 10294 or mechanica-tube standards.
• Industries: General machinery, mining and metallurgical equipment, petrochemical components, pulp and paper machinery, pump/valve and hydraulic blanks, offshore and seawater components, non-process-side structures in food and pharma equipment.
• Boundary to “pipe”: Hollow bar is not a pressure pipe. For pressure service, project specifications and code add-ons must be written into the contract and verified.
• Supply forms: As-rolled black surface or solution-annealed and pickled (HRAP). Optional OD/ID machining allowance and end finish per project.
2. Standards Matrix (by use and alloy family)
• Hollow-bar and mechanica-tube base:
— EN 10294-1: Hollow bars for machining — non-alloy and alloy steels.
— EN 10294-2: Hollow bars for machining — stainless steels.
— EN 10297-1: Seamless circular steel tubes for mechanical and general engineering purposes.
— EN 10305-1: Cold-drawn precision seamless tubes (for tight tolerances and surface).
— ASTM A519: Seamless carbon and alloy steel mechanical tubing.
— ASTM A511: Seamless stainless steel mechanical tubing.
• Dimensions & tolerances (stainless and negotiated cases): ISO 1127 as a reference when stainless “tube route” is adopted for hollow-bar use.
• Nondestructive testing: EN ISO 10893 series (UT, ET, RT, MT, PT methods and levels).
• China/Japan cross-references: GB/T 8162, GB/T 3639, GB/T 14975／14976／13296 (when using tube route); JIS G3445, JIS G3459.
• Certifications and witnessing: EN 10204 3.1／3.2.
3. Scenario—Material—Standard—Size Mapping (quick text guide)
• General sleeves and bushings: Materials E355, 20MnV6, 42CrMo4 (AISI 4140). Standards EN 10294-1 or ASTM A519. Typical OD 60–250 mm, WT 10–60 mm, L 4–6 m.
• High strength and fatigue-sensitive rings and couplings: Materials 42CrMo4 (QT), 34CrMo4 (AISI 4130). Standards EN 10294-1 or ASTM A519. Typical OD 80–300 mm, WT 20–80 mm.
• General corrosion-resistant structures (non-process side): Materials 304L, 316L. Standards EN 10294-2 or ASTM A511. Typical OD 50–200 mm, WT 8–40 mm.
• Seawater and high-chloride service: Materials duplex 2205, super duplex 2507. Standard EN 10294-2; if using tube route, add ASTM A789 chemistry and corrosion checks. Typical OD 60–220 mm, WT 10–50 mm.
• High-temperature oxidation or strong-corrosion parts: Materials 310S, Ni-alloys 625, 825, C-276. Standard ASTM A511 or relevant Ni-alloy tube/bar standard plus mill technical conditions. Sizes per capability.
• Tight fit with high ID surface quality: Use EN 10305-1 cold-drawn precision route, or stipulate ID finish and roughness on top of EN 10294; tighten tolerances by agreement.
4. Size Range & Tolerances (negotiable tightening)
• Outside diameter: ~30–250 mm mainstream; larger ODs available subject to mill capability.
• Wall thickness: ~8–80 mm common; thicker walls by project.
• Length: typically 4–6 m; fixed lengths available.
• Straightness: typically ≤1.5 mm/m; tighter limits per project.
• Eccentricity & ovality: write explicit limits into the PO; typical eccentricity ≤10%. Ovality per EN 10294 or agreement.
• Tolerance system: follow EN 10294-1／-2 for OD/WT/length/straightness; if supplied to ASTM A519 or ASTM A511, apply those standards’ tolerance clauses; for stainless tube route, ISO 1127 D/T classes may be adopted by agreement.
5. Manufacturing Flow & Key Controls
• Steelmaking & refining: EAF/BOF with AOD/VOD; ESR as needed; ensure low S/P and cleanliness.
• Forming: Mannesmann piercing with hot rolling or hot extrusion to thick-wall hollows; control wall uniformity and concentricity.
• Heat treatment: Normalize or quench & temper for C-Mn/alloy; solution anneal and rapid cool for stainless to avoid harmful phases.
• Straightening & NDT: Straighten and test per EN ISO 10893 series (UT/ET/MT/PT); 100% UT recommended for critical parts.
• Machining allowance & ends: Define OD/ID allowances; face and chamfer ends for clamping and boring.
6. Quality Checks & Documentation
• Chemistry & PMI: per grade and standard; positive material identification at critical points.
• Mechanical properties: YS, UTS, EL, hardness per standard and delivery condition.
• Dimensions & surface: OD, WT, L, straightness, ovality, eccentricity; no laps, cracks, seams, or deep scratches.
• Tightness & pressure: Hollow bar is not a pressure pipe; add leak or pressure tests only if specified for pressure-part blanks.
• Dossier: EN 10204 3.1／3.2, heat-treatment charts, NDT reports, dimensional records, traceability; third-party witnessing as specified.
7. Supply Forms & Packing
• Supply condition: black, pickled, or solution-annealed and pickled (HRAP).
• Protection: stainless pickling and passivation; end caps; rust and moisture protection.
• Marking & traceability: heat/lot, grade, size, length, condition, weight, piece ID; QR if required.
8. Ordering Checklist (copy-paste ready)
1. Standard & edition: EN 10294-1／-2 or ASTM A519／ASTM A511 (year). If tube route is used, add EN 10297-1／EN 10305-1 or ISO 1127 clauses.
2. Grade & condition: e.g., “42CrMo4 + QT”, “1.4462 (2205) solution annealed”.
3. Size & tolerances: OD × WT × L; limits for straightness, eccentricity, and ovality; machining allowance if any.
4. NDT: UT/ET coverage and level; MT/PT if needed.
5. Documents & witnessing: EN 10204 3.1／3.2, heat-treatment charts, NDT reports, TPI list.
6. Packing & logistics: end protection, anti-rust and moisture protection, handling and stacking requirements.
9. Material Selection Guide (text)
• Cost and machining efficiency: E355, 20MnV6 (EN 10294-1).
• Strength and toughness: 42CrMo4 QT or AISI 4140 (ASTM A519).
• General corrosion resistance: 304L, 316L (EN 10294-2 or ASTM A511).
• Seawater/chlorides: 2205 or 2507 (EN 10294-2; add ASTM A789 requirements where applicable).
• High-temperature/strong corrosion: 310S, Alloy 625／825, C-276 (check mill capability and heat-treatment window).
10. Procurement, Installation & O&M Risk Alerts
• Treating hollow bar as pressure pipe without code add-ons creates compliance gaps.
• Missing limits for straightness/eccentricity/ovality leads to scrap after machining.
• No pickling/passivation or iron contamination on stainless surfaces causes early pitting.
• Using 304/316 in seawater/high-chloride service reduces life; switch to duplex or Ni-alloys.
• Not defining EN ISO 10893 methods/coverage risks hidden internal defects.
• Tight-ID applications require agreed ID roughness and finishing plan in advance.
11. Representative Purchase Lines (ready for RFQ/PO)
• Alloy-steel sleeve blank:
“Hollow bar: EN 10294-1 E355 + SR, OD 180 mm × WT 30 mm × L 6 m; machining allowance +2.0 mm OD / +2.0 mm ID; straightness ≤1.5 mm/m; 100% UT (EN ISO 10893-8 level as agreed); EN 10204 3.1.”
• High-strength ring blank (QT):
“Hollow bar: ASTM A519 4140 Q + T (28–32 HRC), OD 260 mm × WT 45 mm × L 5.8 m; UT level E2; ends chamfered; EN 10204 3.1.”
• Stainless corrosion-resistant part:
“Hollow bar: EN 10294-2 1.4404 (316L) HRAP, OD 150 mm × WT 20 mm × L 6 m; pickled & passivated; 100% UT; EN 10204 3.1.”
• Offshore duplex component:
“Hollow bar: EN 10294-2 1.4462 (2205) solution annealed, OD 120 mm × WT 18 mm × L 6 m; phase balance 35–60%; verify ASTM A923 Methods A/B/C and G48-A @ 25 °C; 100% UT; EN 10204 3.2.”
12. Representative Global Producers (alphabetical, examples)
• Alleima (ex-Sandvik Materials Technology): Sanmac hollow bars including duplex series.
• Benteler Steel/Tube: European mechanical tubes and hollow bars.
• OSTP (ex-Outokumpu Stainless Tubular Products): stainless hollow bars and tubes.
• TimkenSteel: alloy mechanical tubing and hollow bars (ASTM A519).
• Tubacex Group: stainless and high-alloy tubes and hollow bars (EN/ASTM systems).
• voestalpine Tubulars: mechanical tubes and hollow bars in Europe.
• Salzgitter Mannesmann: EN 10294-1 hollow bars and stock size systems in Europe.
Hollow Bars｜Technical Specifications
1. Definition and Scope
1. Definition: Hollow bar is a thick-wall, round, cored long product intended for machining (turning, boring). It is produced by piercing plus hot-rolling or hot extrusion, followed by heat treatment, straightening, dimensional control with machining allowances, and NDE. The dedicated European product standards are EN 10294-1 (non-alloy and alloy steels, hollow bars for machining) and EN 10294-2 (stainless steels, hollow bars for machining).
2. Boundary to “pipe/tube”: Hollow bar is supplied as machining stock and shall not be treated as a code-stamped pressure pipe. For pressure service or heat-exchanger use, apply the relevant tube/pipe standards (e.g., ASME/ASTM A312, A213, A269, A789) instead of hollow bar.
3. Typical industries: General machinery, mining and metallurgical equipment, rollers, couplings, bushings and sleeves, pump/valve and hydraulic components (as blanks), offshore/non-media-side structures, paper and fiber machinery.
4. Not for: regulated pressure service unless the applicable codes (ASME/PED) and add-on requirements are fully met by contract.
2. Standards Landscape
2.1 Hollow-bar & mechanical-tube standards
• EN 10294-1: Hollow bars for machining – non-alloy and alloy steels; dimensions, tolerances, technical delivery conditions.
• EN 10294-2: Hollow bars for machining – stainless steels.
• EN 10297-1: Seamless circular tubes for mechanical and general engineering purposes – often referenced for hollow-bar deliveries.
• EN 10305-1: Steel tubes for precision applications – cold-drawn seamless (for tighter tolerances and improved bore finish).
• ASTM A519: Seamless carbon and alloy steel mechanical tubing (commonly used in the U.S. as a hollow-bar equivalent).
• ASTM A511/A511M: Seamless stainless steel mechanical tubing (for stainless hollow-bar deliveries).
• ISO 1127: Stainless steel tubes – dimensions and tolerances (used as a negotiated reference when pipe-route products are supplied as hollow-bar blanks).
• EN ISO 10893 series: NDT of steel tubes (UT/ET/RT/MT/PT) – to be specified for hollow-bar/mechanical-tube NDE.
2.2 Common supporting standards in China/US/Japan
• China GB/T: GB/T 8162 (structural seamless), GB/T 3639 (cold-drawn precision seamless); stainless routes GB/T 14975 (structural), GB/T 14976 (fluid), GB/T 13296 (boiler/heat-exchanger) when pipe-route is used as hollow-bar blanks.
• US ASME/ASTM (pipe/tube for pressure service, for boundary clarification): A312, A213, A269, A789.
• Japan JIS: G3445 (machine structural carbon steel tubes), G3459 (stainless steel pipes).
Note: ISO 2938 (“Steel — Hollow bars for machining”) has been withdrawn; use EN 10294 series instead.
3. Grades (examples)
• Carbon & low-alloy: E355 (1.0580), 20MnV6 (1.5217), 42CrMo4 (1.7225 ≈ AISI 4140), 34CrMo4 (≈ 4130), E470/E590 – for general machining, couplings, sleeves and rollers.
• Stainless: 304/304L (1.4301/1.4307), 316/316L (1.4401/1.4404), 321, 347, 310S, 904L (1.4539), 6Mo (UNS S31254, 1.4547), duplex 2205 (1.4462), super duplex 2507 (1.4410).
• Nickel alloys: Alloy 625 (UNS N06625), 825 (UNS N08825), Hastelloy C-276 (UNS N10276) – for severe corrosion/high-temperature carburizing; typically supplied per A511 or per manufacturer’s conditions.
4. Manufacturing and Heat Treatment (Process and Control Essentials)
• Melting and billets: EAF/BOF → AOD/VOD (for stainless steel) refining; ESR when required; supply as continuous-cast billets or ingots.
• Forming: Piercing (Mannesmann) plus hot rolling or hot extrusion to produce a thick‑wall hollow shell; when necessary, perform rough machining after heat treatment to control machining allowance.
• Heat treatment:
– Carbon/alloy steels: Normalizing; quench‑and‑temper (Q+T); or normalize plus temper, to achieve the required strength, toughness, and machinability.
– Stainless steels: Solution annealing (typically ≥1040 °C, per the applicable grade standard) followed by rapid cooling to prevent precipitation of deleterious phases (σ/χ).
• Straightening and NDE: In‑line or off‑line straightening; carry out UT/ET/MT/PT in accordance with the EN ISO 10893 series (coverage as specified by the project). Because hollow bar is commonly supplied as a machining blank, control straightness and residual stress in the delivery condition to reduce distortion during subsequent turning.
• Machining allowance and ends: Define OD and ID machining allowances; face and chamfer ends to facilitate later clamping and boring.
5. Dimensions, Wall Thickness & Tolerances
Typical stock OD ranges around 30–250 mm (wider ranges available depending on mill capability). Apply EN 10294-1/-2 tolerances for OD, wall and length when hollow-bar route is specified; for pipe-route products (A519, A511, EN 10297-1, EN 10305-1), tolerances follow the respective tube standards; for stainless, ISO 1127 tolerance classes can be referenced by agreement. Specify limits for wall-thickness eccentricity, ovality and straightness in the PO.
6. Surface & Cleanliness
Supply as black or pickled/shot-blasted; no laps, folds, cracks or deep scratches. Stainless hollows shall be pickled and passivated (or mechanically de-contaminated) to minimize pitting initiation; specify cleanliness and residuals for clean-service industries.
7. QA/QC & Testing
Chemistry (incl. PMI if required); tensile/elongation/hardness per standard and HT condition; NDE per EN ISO 10893 (coverage to be defined, e.g., 100% UT for critical parts); dimensional checks (OD/WT/length/straightness/ovality/eccentricity); hydro/helium tests only when contractually required; documentation per EN 10204 3.1/3.2.
8. Service–Grade–Standard–Size Mapping (text quick guide)
• General machining (bushings, sleeves, couplings): E355, 20MnV6, 42CrMo4 → EN 10294-1 → prioritize stock OD 30–250 mm.
• High strength & toughness: 42CrMo4 Q&T or AISI 4140 → EN 10294-1 or ASTM A519.
• Corrosion-resistant (food, paper, general chemical): 304L/316L → EN 10294-2 or ASTM A511 → tolerances negotiable per ISO 1127.
• Chloride/sea-water/offshore: Duplex 2205/2507 → EN 10294-2; or pipe-route with ASTM A511/A789 as applicable.
• High-temperature/severe corrosion: 310S, Alloy 625/825, C-276 → per A511 or manufacturer’s spec with HT/structure control.
9. Ordering Checklist
Standard & edition (EN 10294-1/-2; or ASTM A519/A511; add EN 10297-1/EN 10305-1/ISO 1127 if pipe-route); grade & HT condition; OD × WT × length; limits for straightness/ovality/eccentricity; NDE method & coverage; documentation (EN 10204 3.1/3.2); end protection, rust prevention and marking.
10. Pitfalls (corrections & avoidance)
Misusing hollow bar as pressure pipe; relying on withdrawn ISO 2938; missing eccentricity/straightness limits; inadequate stainless de-contamination; using 304/316 in high-chloride service; insufficient NDE per EN ISO 10893.
11. Selection Guide (summary)
Cost-efficient machining → E355/20MnV6; strength/toughness → 42CrMo4 (Q&T)/4140 (A519); general corrosion → 304L/316L (EN 10294-2 or A511); chloride/sea-water → 2205/2507 (EN 10294-2 or A789 via pipe-route); high-T/corrosion → 310S/625/825/C-276 (confirm manufacturability & HT window).
12. Representative Global Manufacturers (examples, A–Z)
Alleima (Sanmac® hollow bar); Benteler Steel/Tube; OSTP; TimkenSteel; Tubacex Group; voestalpine Tubulars; Salzgitter Mannesmann/T&S distribution.
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