GB/T 34105 Seamless Steel Tubes for Ocean Engineering Structures

GB/T 34105 seamless steel tubes are designed for load-bearing offshore and marine engineering structures that require controlled strength, low-temperature toughness, weldability, and consistent dimensional performance.

The tubes are suitable for fabricating structural members exposed to wave loading, vibration, impact, cyclic stress, and low-temperature marine environments. Available strength grades range from Q245H to Q690H, with quality classes selected according to the specified Charpy impact test temperature.

Production may include hot rolling, heat treatment, straightening, ultrasonic testing, dimensional inspection, tensile testing, and impact testing. Grade, quality class, dimensions, delivery condition, inspection scope, and certification requirements should be confirmed in the purchase order.

Specifications

Dimensions outside the stated production range should be reviewed against the selected grade, wall thickness, heat-treatment route, testing frequency, and minimum order quantity.

Main Characteristics

Controlled Yield Strength

The grade designation indicates the nominal minimum yield-strength level. The standard includes structural steel grades from approximately 245 MPa to 690 MPa minimum yield strength, allowing engineers to balance structural capacity, tube weight, weldability, and fabrication cost.

Low-Temperature Impact Toughness

Quality-class suffixes are used to distinguish impact-test requirements. Depending on the selected grade and class, Charpy V-notch testing may be specified at temperatures including 20°C, 0°C, −20°C, −40°C or −60°C.

For offshore projects, the quality class must therefore be stated together with the grade. Ordering “Q345H” without an impact class is not sufficient for confirming low-temperature suitability.

Seamless Structural Integrity

The seamless manufacturing route avoids a longitudinal weld seam. This provides uniform circumferential geometry and makes the tube suitable for structural members subjected to bending, axial loading, torsion, vibration and multi-directional fatigue loading.

Weldability Control

Low-carbon and microalloyed compositions are used to achieve the specified strength and toughness. Carbon equivalent, product thickness, heat input, preheating temperature, consumable selection and post-weld procedures should be reviewed before fabrication.

Traceable Mechanical Performance

Each production heat can be linked to chemical analysis and mechanical test records. For critical offshore projects, heat-number traceability, tube-by-tube identification, ultrasonic inspection records and inspection certificates can be included in the documentation package.

Our Advantages

1. Grade and Impact-Class Verification Before Production

A common procurement risk is specifying only the strength grade while omitting the required Charpy impact temperature.

Before production, we review:

• Design temperature

• Required quality class

• Tube wall thickness

• Heat-treatment condition

• Charpy test temperature

• Minimum absorbed energy

• Project or classification-society requirements

This prevents the supply of a tube that meets room-temperature tensile requirements but does not satisfy the project’s low-temperature toughness requirements.

2. Wall-Thickness and Heat-Treatment Matching

Mechanical properties, especially yield strength and toughness, may vary with wall thickness and delivery condition.

We match the manufacturing route to the ordered grade:

• Normalizing for stable microstructure and toughness

• Normalizing and tempering where required

• Quenching and tempering for higher-strength grades

• Controlled cooling for consistent properties through the wall

• Representative mechanical testing based on the agreed inspection lot

The final mill certificate identifies the actual heat-treatment condition and reported test results.

3. Project Documentation and Traceability

Offshore fabricators often require more than a basic commercial certificate.

Available documentation can include:

• Inspection certificate

• Heat analysis

• Product analysis when specified

• Tensile-test report

• Charpy impact-test report

• Ultrasonic-testing report

• Dimensional inspection report

• Heat-treatment record

• Tube marking and packing list

• Third-party inspection endorsement

• Material traceability list

Documentation requirements should be stated at the quotation stage to ensure that testing and record retention are included in the production plan.

Execution Standards

Specific Application

Offshore Platform Leg Bracing

GB/T 34105 seamless tubes can be used to manufacture tubular diagonal bracing for offshore platform support structures.

The bracing members transfer axial, bending and cyclic loads generated by:

• Wave action

• Wind loading

• Platform vibration

• Equipment operation

• Installation loads

• Repeated environmental loading

For this application, the purchaser should specify the required grade, quality class, design temperature, dimensions, corrosion allowance, weld procedure, ultrasonic-testing level, coating system and third-party inspection requirements.

Chemical Composition

The following table provides a practical procurement reference for five commonly specified strength levels. Final acceptance must be based on the ordered grade, quality class, product thickness, heat analysis, applicable table in GB/T 34105-2017, and the mill inspection certificate.

Values are mass fractions in percent.

Mechanical Properties

Quality-Class and Impact-Test Guidance

Inspection and Testing

Depending on the order and grade, inspection may include:

• Heat chemical analysis

• Product chemical analysis

• Tensile testing

• Charpy V-notch impact testing

• Flattening or bend testing where applicable

• Ultrasonic testing

• Visual surface inspection

• Outside-diameter measurement

• Wall-thickness measurement

• Length and straightness inspection

• End inspection

• Marking verification

• Third-party inspection

The ultrasonic testing level, test frequency, acceptance criteria and inspection-document type should be specified in the inquiry.

Ordering Information

A complete inquiry should include:

• Standard: GB/T 34105-2017

• Steel grade and quality class

• Outside diameter

• Wall thickness

• Length

• Quantity or total weight

• Delivery condition

• Design temperature

• Charpy test temperature and absorbed energy

• Dimensional tolerance requirements

• Straightness requirements

• Ultrasonic-testing requirements

• End preparation

• Surface protection or coating

• Inspection-document type

• Third-party or classification-society inspection

• Marking and packing requirements

Correct definition of these parameters is essential because nominally similar offshore structural tubes may differ significantly in low-temperature toughness, weldability, dimensional accuracy, inspection scope and documentation.