BS 1387 Standard Q195 SS400 Welded Galvanized Steel Tube in Round Shape for Structural Applications

BS 1387 welded galvanized steel tube is a circular carbon-steel tube intended for threaded, welded, and general structural service. It is commonly supplied with plain, threaded, or threaded-and-socketed ends and with either a zinc-coated or black surface.

For technically accurate procurement, the tube specification and raw-material grade must be stated separately. BS 1387 defines the finished tube requirements, while Q195 and SS400 are base-material designations under GB/T 700 and JIS G 3101 respectively. They should not automatically be treated as BS 1387 grades without confirming the finished tube's dimensional, mechanical, coating, threading, and test compliance.

The longitudinal ERW process permits stable outside diameter, wall thickness, and roundness for threading, roll forming, bending, welding, and mechanical assembly. Dimensional tolerances must be selected from the ordered pipe standard rather than from the raw-material standard.

BS 1387 traditionally classifies tubes into light, medium, and heavy series. The selected series determines the wall thickness and mass per metre. Substituting a general structural tube with the same nominal diameter is not sufficient unless its actual outside diameter, wall thickness, threading compatibility, and pressure or leak test requirements are verified.

The zinc layer provides sacrificial protection to the steel substrate. Coating durability depends on zinc mass, coating continuity, exposure category, condensation, chloride contamination, cut-edge protection, and damage during bending or installation.

The tube may be supplied plain-ended, threaded, or threaded and socketed. Threads, end preparation, coating condition, and weldability must be specified at the ordering stage. Galvanized surfaces should be locally prepared before welding, and welding fumes must be controlled using an appropriate industrial ventilation procedure.

Q195 offers relatively high formability and is suitable for light-duty fabrication. Q235B provides a higher strength level for general welded structures. SS400 is a JIS structural grade with a minimum yield strength of 245 MPa for thicknesses up to 16 mm. Legacy Q345B provides higher strength, but current GB/T 1591 procurement should normally evaluate Q355-series grades instead of assuming that Q345B remains the current designation.

A frequent procurement problem is ordering "BS 1387 Q195 SS400 pipe" without defining which requirement controls the finished tube.

We separate the purchase specification into:

• Finished tube standard
• Base-steel grade
• Dimensional series
• Manufacturing route
• Coating route and coating mass
• End preparation
• Inspection and testing level

This prevents Q195 or SS400 raw material from being incorrectly presented as automatic proof of BS 1387 compliance. SS400 is a general structural steel designation under JIS G 3101 rather than a dedicated BS 1387 pipe grade.

Buyers often receive quotations that state only "galvanized," without identifying whether the material is pre-galvanized or galvanized after welding.

We define:

• Galvanizing route
• Minimum zinc mass or thickness
• Weld-seam repair method
• Internal and external coating requirements
• Cut-end repair requirements
• Coating adhesion test
• Coating-thickness measurement method

This allows the purchaser to evaluate the tube according to the actual atmospheric, indoor-condensation, or fabrication environment rather than relying on an undefined galvanized finish.

Nominal pipe size does not directly represent the measured outside diameter. A nominal 1-inch threaded tube, for example, is not a tube with an actual outside diameter of 25.4 mm.

Before production, we can confirm:

• Actual outside diameter
• Wall thickness and series
• Thread size and thread standard
• Socket compatibility
• Length tolerance
• End squareness
• Ovality
• Straightness
• Mass per metre

This reduces thread mismatch, coupling leakage, fixture interference, and installation rework. ISO 65 similarly treats carbon-steel threading tubes through defined dimensional series rather than nominal-inch dimensions alone.

The tube can be used to manufacture a commercial greenhouse roof arch.

For this application, the purchaser should define the outside diameter, wall thickness, zinc coating route, bending radius, ovality after bending, weld-seam orientation, minimum yield strength, and local repair method for drilled or cut areas. Pre-galvanized Q195 tubing is suitable for light formed arches when the structural design permits, while higher-strength grades may be selected for longer spans or increased wind and snow loads.

The final tube dimensions and structural grade must be verified by the greenhouse designer. This product description does not replace project-specific structural calculations.

The following values are typical maximum heat-analysis limits from the referenced material standards. The exact grade suffix, deoxidation practice, product thickness, and ordered standard edition must be stated on the purchase order.

Recommended inspection items include: