How to Ensure You Get the Right Honed Tube for Hydraulic Applications

Honed tubing is now the first choice for hydraulic equipment.  Its characteristics include excellent sealing properties, stable operation, and extended service life, similar to hydraulic cylinders. However, choosing the right honed tubing specifications to match your hydraulic

cylinder project design and operating conditions is crucial.

Incorrectly selected honed tubing can lead to seal lip damage, leakage, stick-slip, and scratches, requiring frequent repairs.  Properly selected honed tubing provides consistent sealing and longer maintenance intervals, eliminating the need for extensive refurbishment work later on.

 We've listed some possibilities you might encounter and how you can avoid them:

Key Factors for Choosing a Honed Tube

Size and Diameter

Let's take an example: after purchasing honed tubes, the cylinder assembly went smoothly, but during use, leakage and sticking occurred. This was simply because they only checked the cylinder diameter and neglected the tolerance grade and the complete tolerance combination.Two points should be noted.:

lPay attention to the finished product's inner diameter (after grinding), not just the steel pipe dimensions.

lSpecify the tolerance grade (H8, H7) according to the piston design drawings.

If you have marked H8 on your drawings, you will need to use ISO terminology. The hole basis system and tolerance grades are mentioned in ISO 286-2, which is very important for you because it reduces the likelihood of incompatibility between pipes and seals.  Additionally, two other points need to be considered:

lFinished product inner diameter tolerance (e.g., 80 H8)

lMeasurement method/acceptance criteria (number of measurement points, distance from pipe end, roundness/straightness), etc.

Material Selection

So, are there any specific considerations regarding material selection? Yes, there are. In our outdoor hydraulic equipment, the tubing meets the tensile strength requirements in practical applications, but it fails due to factors such as welding heat input, bending loads, and fatigue corrosion. What's the reason for this?

Typically, hydraulic cylinders are manufactured using non-alloyed honed tubes such as E355/ST52, due to their high strength and good machinability.  Refer to the comparison table for DIN ST52 and EN E355 (1.0580); these are similar grades.

If you want to purchase American standard honed tubing, then ASTM A519 is a suitable standard.  It is widely used for seamless mechanical tubing and applies to both hot-rolled and cold-rolled processes. When purchasing, pay attention to the material condition and grade, as this will affect the consistency and machinability of the tubing.

Corrosion is also an important factor affecting hydraulic honing tubes.  Corrosion occurs when the honing tube is frequently exposed to liquids. Switching to stainless steel is a good option, such as 304 or 306, which may be more cost-effective than rebuilding. However, it's important to note that the surface finish/tolerance still needs to be specified, because stainless steel cannot "tolerate" poor surface treatment in the sealing area.

When purchasing materials, specifying the material grade, delivery terms, and inspection documents are all very important.

Surface Finish Importance

Many seal failures aren’t “bad seals”—they’re surface engineering

To understand this, you need to know two key points:

lThe surface must be smooth enough to avoid cutting the sealing ring.

lThe surface also needs texture to maintain lubrication.

However, these two points are contradictory. If the surface is too smooth, it will reduce oil film retention, increase friction/heat generation, and thus shorten the lifespan of the seal.  Conversely, a surface that is too rough will cause leakage and accelerate wear.

Under typical procurement conditions, the inner surface roughness of honed tubes is usually Ra 0.2–0.4 μm.  In unit conversion, Ra 0.4 μm ≈ 16 μin.

You can specify Ra + any additional texture requirements on the purchase order and request a surface roughness report for first article/PPAP approval.

Honing Tube Manufacturing Process

Most people usually focus only on the price and disregard the manufacturing process, but the manufacturing process is the crucial reason why two pipes of the same size perform differently in sealing applications.

Honing tubes actually involve two different processes:

lHoning: This process involves removing small amounts of material using a grinding stone and ultimately creating a controlled texture on the inner surface. Honing is suitable for various sizes.

lSkiving + Roller Burnishing: This is a machining process that combines cutting and polishing, allowing for efficient production of tubing. It integrates cutting and polishing into a single die.

Manufacturing Precautions

Even with appropriate process control, defects can still occur due to improper handling. These defects may not be apparent during production but will become visible after assembly. Common problems include taper, barreling, surface irregularities, and poor cleanliness.

You need to pay attention to this information:

lStraightness and alignment (so that the honing process does not "follow the curvature" and produce taper/ovality).

lCleanliness after completion (grinding residue can damage the seals in the hydraulic oil circuit)

lNo random scratches/spiral tool marks; the stable surface is conducive to lubricant retention.

When making your purchase, please pay attention to cleanliness and quality.

Match the Honed Tube to the Application

We believe that after reading this purchasing guide, you will have a better understanding of how to purchase honed tubes. If you have any further questions or requirements, please contact TORICH Group and provide your cylinder drawings (or detailed information on cylinder bore/piston rod/seals). We will help you select, design, and manufacture honed tubes suitable for your project. Contact us today!