GB/T 33156 Cold-Drawn Precision Welded Steel Tubes for Gas Springs

GB/T 33156 cold-drawn precision welded steel tubes are designed for manufacturing the pressure cylinders of gas springs. The tubes are produced from electric-resistance-welded hollows followed by cold drawing or cold rolling, providing contrkness, improved concentricity and a smooth internal surface.

The dimensional accuracy and internal surface quality are particularly important because the tube normally works directly with the piston, guide, sealing element and pressurized nitrogen chamber. Stable tube geometry helps reduce seal wear, gas leakage, friction variation and inconsistent extension force.

GB/T 33156-2016 is the current dedicated Chinese product standard for precision welded tubes for gas springs. A national revision project is presently consolidating GB/T 33156-2016 and GB/T 31315-2014 into a broader standard for cold-drawn or cold-rolled precision welded structural tubes.

Specifications

Controlled Inside Diameter

The inside diameter can be controlled as the primary ordered dimension. This is important when the gas-spring piston, guide bush and sealing package operate directly against the tube bore.

For selected sizes, ID tolerances can be controlled within approximately ±0.03–0.05 mm, subject to wall thickness, reduction ratio and heat-treatment condition.

Smooth Internal Working Surface

Precision cold drawing reduces weld-line irregularity and improves the internal surface compared with ordinary ERW tubing. Internal surface roughness down to approximately Ra 0.4 μm is available for gas-spring cylinder applications.

A smoother bore helps:

• reduce dynamic seal abrasion;
• stabilize breakaway friction;
• limit internal scoring;
• improve gas retention during repeated compression cycles.

Improved Concentricity

Cold drawing through a die and over a mandrel simultaneously corrects the outside diameter, inside diameter and wall distribution. This provides more consistent concentricity than standard as-welded mechanical tubing.

Improved concentricity helps maintain uniform clearance between the piston assembly and cylinder bore.

Consistent Weld Zone

The original ERW weld is cold worked together with the tube body. Depending on the delivery condition, subsequent stress relieving, annealing or normalizing reduces the difference between the weld area and the parent material.

Weld integrity can be verified by eddy-current testing, flattening tests and destructive section inspection.

Predictable Mechanical Condition

The tube can be supplied in different delivery conditions:

Our Technical Advantages

1. Bore Quality Is Controlled as a Functional Surface

A gas-spring buyer is not only purchasing a steel tube; the internal bore becomes part of the sealing and sliding system. Common procurement concerns include rough weld lines, longitudinal scratches, drawing marks and inconsistent roughness.

Our inspection plan can therefore include:

• internal roughness measurement;
• bore visual inspection;
• endoscopic inspection for selected sizes;
• plug-gauge or air-gauge ID verification;
• control of longitudinal drawing marks;
• cleanliness inspection after cutting.

This reduces the risk of premature seal wear and unstable operating friction.

2. Dimensional Capability Is Confirmed by Actual Tube Size

A single tolerance value is not technically valid for every combination of diameter and wall thickness. Thin-wall tubes, small-diameter tubes and low diameter-to-wall ratios respond differently during cold drawing and heat treatment.

Before production, the ordered dimensions are reviewed for:

• OD-to-wall-thickness ratio;
• required ID tolerance;
• heat-treatment shrinkage;
• straightness after cutting;
• achievable concentricity;
• required machining allowance.

The inspection report can include OD, ID, wall thickness, ovality and straightness records instead of reporting only the nominal tube size.

3. Weld and Pressure-Retention Risks Are Addressed Separately

Dimensional compliance alone does not confirm that the welded tube is suitable for a pressurized gas-spring cylinder.

A suitable quality plan can combine:

• eddy-current testing of the full tube length;
• flattening or drift-expansion testing;
• weld-macro examination;
• tensile testing;
• hydrostatic or pneumatic leakage testing when specified;
• traceability from steel coil to finished production batch.

This separates surface-related, dimensional and weld-integrity risks rather than relying on one final inspection.

Execution Standards

Office-Chair Height-Adjustment Gas Spring Cylinder

The tube is used as the outer pressure cylinder of a height-adjustment gas spring installed in an office-chair lift column.

In this component, the tube must:

• contain pressurized nitrogen;
• provide a smooth sliding surface for the piston and seal assembly;
• maintain consistent internal diameter along the working stroke;
• resist permanent expansion under operating pressure;
• remain straight after cutting, end forming and assembly;
• support repeated height-adjustment cycles without leakage.