Precision Tube Cluster
DIN 2391 ST52 Honed-Bore Tubes — hydraulic cylinder spec
Procurement guidance for ST52 / E355 cold-drawn seamless tubes with H8 or H9 honed bores for hydraulic cylinders.
📅Last reviewed
DIN 2391 ST52 honed-bore tubes are cold-drawn seamless precision tubes, usually supplied as E355 in BK+S condition, with the inside diameter finished to H8 or H9 for hydraulic cylinder barrels. Specify OD, ID, wall, bore tolerance, Ra roughness, straightness, length, and EN 10204 3.1 MTC.
When should procurement ask for DIN 2391 ST52 honed-bore tubes?
Ask for DIN 2391 ST52 honed-bore tubes when the tube will become a hydraulic cylinder barrel and the piston seal runs directly on the ID. Commodity seamless or ERW tube is not enough because bore tolerance, roundness, roughness, and straightness control leakage.
The phrase “DIN 2391 ST52 honed bore” normally describes a seamless precision tube that has been cold drawn, stress relieved, and ID-finished for cylinder service. The older DIN material name ST52 maps closely to E355 under EN 10305, but buyers still use ST52 in RFQs because many hydraulic drawings, service teams, and Indian stock lists were built around the DIN vocabulary. The purchase order should accept “ST52 / E355 as per MTC” only when the mechanical properties and delivery condition match the drawing.
A hydraulic cylinder barrel is not just a pressure tube. It is also the bearing surface for the piston seal. The inside diameter must be controlled tightly enough for seal squeeze, must be round enough to avoid local bypass, and must be smooth enough to protect the seal lip without becoming so polished that oil retention is poor. DIN 2391 and EN 10305 provide the manufacturing basis; ISO 286 explains the H8/H9 tolerance language; ISO 4287 defines the roughness parameters that should appear on the inspection report.
For RP Sales enquiries, the practical RFQ line is: OD x ID or OD x wall, grade ST52/E355, condition BK+S, honed ID H8 or H9, Ra value, length, quantity, MTC requirement, and whether fixed-length cutting or machining allowance is needed. If the drawing has chrome-plated rod, seal, and pressure details, attach it so the tube is not selected only from a catalogue size.
How do H8 and H9 bore tolerances change cylinder performance?
H8 is the tighter bore tolerance and is preferred for higher-pressure or better-seal cylinders. H9 is easier to source and cheaper for general industrial cylinders. Selection should follow seal catalogue limits, pressure, stroke speed, and acceptable internal leakage, not price alone.
The H-class is an ISO 286 hole-basis tolerance applied to the cylinder bore. At small and medium bores, the difference between H8 and H9 may look minor on paper, but it changes piston seal compression, breakaway friction, and bypass leakage. H8 is usually chosen where repeatable motion, higher pressure, or better seal life matters. H9 is common where the duty is moderate and cost or availability is more important.
Do not specify H8 automatically. Tighter tolerance means more finishing time, more rejection risk, and sometimes longer lead time. If the piston assembly, guide rings, or seals are designed for H9, buying H8 may not deliver a visible benefit. Conversely, using H9 against a seal designed around H8 can create uneven compression and early leakage. The supplier can provide the tube, but the cylinder designer owns the fit decision.
The inspection report should state actual bore size, tolerance class, and measurement method. A single nominal ID is not enough. For long barrels, ask for straightness and ovality checks because a locally good bore can still create assembly issues if the tube bows over the stroke length.
What does BK+S mean for ST52 hydraulic cylinder tubes?
BK+S means the tube is cold drawn and stress relieved after drawing. It retains the dimensional accuracy and strength benefits of cold work while reducing residual stress. That matters when the tube is honed, cut, welded to ports, or machined at the ends.
Cold drawing improves dimensional accuracy and mechanical strength, but it also introduces residual stress. A tube supplied hard as drawn may move during deep machining, port welding, or end boring. BK+S, often translated as stress-relieved after cold drawing, is the common compromise for hydraulic barrels: strong enough for service, stable enough for finishing, and widely recognised in DIN 2391 and EN 10305 procurement.
ST52/E355 is popular because its yield strength suits many mobile, agricultural, and industrial cylinders without requiring alloy steel pricing. The exact chemistry and mechanical values should come from the EN 10204 3.1 MTC. Buyers should check heat number, grade, delivery condition, tensile strength, yield strength, elongation, and any hardness value required by the cylinder drawing.
If the cylinder barrel will be welded, confirm whether the welding procedure is qualified for the delivered condition. Stress relief does not remove the need for correct preheat, filler, and post-weld controls where the drawing demands them. For simple welded ports on common cylinders, BK+S E355 is standard, but safety-critical hydraulic assemblies deserve drawing-led review.
Which surface-finish value should appear on a honed-bore tube RFQ?
Use an ISO 4287 roughness value such as Ra, and state the maximum value expected on the bore. Many hydraulic cylinder RFQs use Ra 0.2-0.4 micrometre after honing. Also confirm cross-hatch quality, cleanliness, and protection from rust during transit.
Surface finish is often written as “mirror finish” or “honed finish”, but those phrases are not measurable enough for inspection. ISO 4287 defines profile roughness terms such as Ra. A common buyer requirement for honed hydraulic barrels is Ra up to about 0.4 micrometre, while some high-performance seals ask for tighter or multi-parameter controls. If the seal supplier mentions Rz, Rmax, or bearing ratio, copy that requirement into the RFQ rather than simplifying it to Ra only.
Honing leaves a controlled cross-hatch pattern that helps retain oil. A bore that is too rough cuts seals; a bore that is too smooth can starve the contact of lubricant. Cleanliness also matters. Abrasive residue from finishing must be removed because it can score the piston seal during first commissioning.
For dispatch, request oiled bore protection, capped ends where practical, and handling that avoids dents on the ID mouth. A tube can meet DIN 2391 and still become scrap if the honed surface is rusted, dented, or contaminated before machining.
Specifications
| Tolerance class | ID H8 or H9 per ISO 286; OD and wall per DIN 2391 / EN 10305 agreement |
|---|---|
| OD / ID range | Common hydraulic sizes from about 30-250 mm OD; quote by OD x ID or OD x wall |
| Surface finish | Honed bore, typically Ra 0.2-0.4 micrometre per ISO 4287 where specified |
| Material grade | ST52 / E355, normally supplied with EN 10204 3.1 MTC |
| Delivery condition | BK+S cold drawn and stress relieved; fixed or random lengths by order |
| Documentation | MTC, dimensional report, bore tolerance report, roughness report on request |
Standards cited for DIN 2391 ST52 Honed-Bore Tubes
Reference standards cited on this page
- DIN 2391-1:1994 — Seamless precision steel tubes — Technical delivery conditions (Deutsches Institut für Normung)
- EN 10305-1:2016 — Steel tubes for precision applications — Seamless cold-drawn tubes (European Committee for Standardization (CEN))
- EN 10305-4:2016 — Seamless cold-drawn tubes for hydraulic and pneumatic power systems (European Committee for Standardization (CEN))
- ISO 286-1:2010 — Geometrical product specifications — ISO code system for tolerances on linear sizes (International Organization for Standardization)
- ISO 4287:1997 — Surface texture — Profile method — Terms, definitions and surface texture parameters (International Organization for Standardization)
- EN 10204:2004 — Metallic products — Types of inspection documents (European Committee for Standardization (CEN))
Related to DIN 2391 ST52 Honed-Bore Tubes
Frequently asked questions
Need Steel Pipes in Bulk?
Get a same-day quotation with competitive pricing. We supply across UP, Bihar, MP & Delhi NCR.