Steel Tube Rolling and Welded Splicing Technology for Marine Steel Structures

Literature Overview

The paper by Li Tongyue and colleagues from Offshore Oil Engineering (Qingdao) Co., Ltd., published in Petroleum and Chemical Industry Equipment (2022, Vol. 25, No. 1), addresses the critical manufacturing process of rolled and welded steel tube splicing for marine steel structures. As offshore platform development intensifies globally, the demand for large-diameter, thick-walled steel tubes has grown substantially. When commercially available seamless or welded pipe dimensions are insufficient for structural requirements—particularly for columns, bracing members, and node tubes—steel plates must be rolled and welded into tubes and then spliced end-to-end to achieve required lengths. This paper systematically documents the manufacturing process flow, methodology, and quality control considerations for this essential fabrication technique.

Process Flow and Technical Methodology

Complete Manufacturing Sequence

The steel tube rolling and splicing process follows a defined sequence of operations:

Sequence	Operation	Key Technical Parameters	Quality Control Point
1	Material preparation	Plate grade, thickness, dimensions	Mill certificate verification, visual inspection
2	Cutting and beveling	Cut length, bevel angle (typically 30°±2°)	Dimensional check, bevel angle verification
3	Plate rolling	Roll gap, rolling force, diameter accuracy	Diameter measurement, ovality check
4	Circumferential welding	Weld process, parameters, sequence	UT/RT inspection of circumferential weld
5	Straightening and sizing	Final diameter, wall thickness, roundness	Geometric dimensional inspection
6	End preparation	Bevel geometry, fit-up gap	Fit-up inspection, gap measurement
7	Longitudinal splicing weld	Weld process, parameters, sequence	UT/RT inspection of splice weld
8	Post-weld treatment	PWHT if required, dimensional correction	Temperature monitoring, dimensional re-check
9	Final inspection	NDT, dimensional, hydrostatic test	Comprehensive acceptance testing

Rolling Process Considerations

The plate rolling operation is the foundational step that determines the geometric quality of the tube. Key considerations include:

Rolling force calculation: Determined by plate thickness, yield strength, roll diameter, and final tube diameter. For thick plates (t > 30 mm), multiple rolling passes may be required.
Diameter accuracy: The rolled tube diameter must meet tolerance requirements, typically ±0.5% of nominal diameter or as specified by applicable standards (e.g., API 5L, EN 10216).
Elongation and strain: The plate undergoes plastic deformation during rolling, with strain concentrated at the neutral axis. Excessive elongation can lead to dimensional issues and residual stress problems.
Residual stress from rolling: The rolling process introduces residual stresses that must be accounted for in subsequent welding operations to prevent distortion.

Welding Process Selection and Parameters

The welding of both circumferential seams and longitudinal splice joints requires careful process selection based on wall thickness, material grade, and applicable codes:

For circumferential welds:

Submerged Arc Welding (SAW) is preferred for thick plates due to high deposition rate and deep penetration
Multi-pass welding with proper interpass temperature control (typically 100-250°C depending on material)
Welding sequence designed to minimize distortion, typically symmetric from the seam

For longitudinal splice welds:

Process selection depends on accessibility and thickness:
SAW with flux cored wire for internal passes
GTAW (TIG) for root pass on thin sections
SMAW for finishing passes where accessibility is limited
Multi-pass welding with controlled layer thickness (typically 6-10 mm per layer for SAW)
Backing ring or backing strip for root pass on through-welding configurations

Welding Procedure Specification (WPS) Key Parameters

Parameter	Typical Range	Rationale
Preheat temperature	100-250°C (depending on Pcm)	Prevent cold cracking in HAZ
Interpass temperature	100-250°C	Control cooling rate, prevent cracking
Heat input	10-30 kJ/mm	Balance between HAZ softening and cooling rate
Welding speed	5-15 cm/min (SAW)	Control heat input and penetration
Wire diameter	3.2-5.0 mm (SAW)	Match thickness and deposition rate
Shielding gas	Ar + 5% CO₂ or pure Ar (GTAW)	Ensure proper arc stability and protection
PWHT temperature	550-650°C (if required)	Reduce residual stresses, relieve HAZ hardness

Quality Control Framework

Non-Destructive Testing Requirements

The quality assurance program for rolled and spliced tubes requires comprehensive NDT coverage:

Circumferential weld: 100% UT inspection (per EN ISO 17635 or equivalent) or RT for critical applications
Longitudinal splice weld: 100% UT or RT inspection, with acceptance criteria per applicable code
Acceptance criteria: Typically Level B or better per EN ISO 17635, or per API 5L requirements for line pipe applications
Rejection criteria: Any indication exceeding the specified acceptance level requires repair and re-inspection

Mechanical Testing and Material Verification

Test Type	Purpose	Standard	Frequency
Tensile test	Verify material properties	ASTM A370 / EN 10002	Per heat/lot
Hardness test	HAZ and weld metal hardness	ASTM E18 / E92	Per WPS qualification
Impact test (Charpy V-notch)	HAZ toughness verification	ASTM E23 / ISO 148	Per WPS qualification
Hydrostatic test	Leak and pressure integrity	API 5L / EN 10216	100% of tubes
Dimensional inspection	Geometric compliance	Applicable product standard	100% of tubes

Engineering Practice Challenges and Countermeasures

Common Defects and Prevention

Defect Type	Root Cause	Prevention / Countermeasure
Cold cracking in HAZ	High hydrogen, high restraint, rapid cooling	Preheat, low-hydrogen consumables, controlled cooling
Porosity in weld metal	Inadequate gas shielding, contaminated surfaces	Surface cleaning, proper gas flow, wind protection
Incomplete fusion	Insufficient heat input, poor fit-up	Proper WPS parameters, fit-up verification
Excessive distortion	Asymmetric welding sequence, high heat input	Symmetric welding sequence, low heat input, clamping
Circumferential seam misalignment	Inaccurate rolling, fit-up error	Precision rolling, gap control, tack welding
Excessive HAZ hardness	High heat input, rapid cooling, high carbon content	Preheat, post-weld cooling control, PWHT

Special Considerations for Marine Environment

Marine steel structures face unique environmental challenges that influence manufacturing quality requirements:

Corrosion resistance: Weld quality directly affects corrosion resistance; porosity and incomplete fusion create corrosion initiation sites
Fatigue performance: Weld defects act as fatigue crack initiation sites; strict NDT acceptance criteria are essential for fatigue-critical connections
Hydrostatic integrity: All tubes must pass hydrostatic testing to ensure pressure containment capability for submerged or splash zone applications
Environmental exposure: Tubes in the splash zone experience the most severe corrosion conditions; weld quality in this region demands highest standards
Repairability: Field welding repair procedures must be qualified and documented for any required in-service repairs

Integration with Applicable Standards

The manufacturing process must comply with multiple applicable standards depending on the project specifications:

Material: ASTM A53, ASTM A106, API 5L, EN 10216-1, GB/T 8162/8163
Welding: ASME Section IX, EN ISO 3834, AWS D1.1, ISO 14732
Inspection: EN ISO 17635, API 5L, NB/T 47013 (Chinese standard)
Product: API 5L for line pipe, EN 10216 for welded tubes, ISO 15590 for hot-dipped galvanized tubes
Marine specific: DNV-ST-F101, DNV-ST-0312, ABS/ Lloyd's class rules

Summary

This paper provides a comprehensive overview of the steel tube rolling and welded splicing technology essential for marine steel structure fabrication. The systematic documentation of the manufacturing process flow, welding methodology, and quality control framework offers practical guidance for engineers and fabricators. The emphasis on weld quality, dimensional accuracy, and comprehensive NDT coverage reflects the critical nature of these components in offshore applications where structural integrity directly impacts safety and environmental protection. The technology described represents a well-established fabrication approach that, when properly executed with rigorous quality control, produces steel tubes meeting all applicable code requirements for demanding marine structural applications.