GB/T 30026-2013 Crane Steel Welding Parameters and Quality Grades

As the specialized standard for crane steel structure welding, GB/T 30026-2013 systematically defines the full chain of technical requirements — from welding procedure qualification to weld quality acceptance. Correctly interpreting and implementing this standard is essential to ensuring weld quality in crane steel structures and guaranteeing safe operation of the equipment. This article provides a detailed breakdown of the standard's core content, helping welding engineers and technicians master process parameter selection and acceptance criteria.

Standard Positioning and Welding System

GB/T 30026-2013 is the dedicated standard for crane steel structure welding. Together with GB/T 30025-2013 (Steel Structure Manufacturing) and GB/T 30027-2013 (Steel Structure Processing and Inspection), it forms the three-part manufacturing standard system for crane steel structures. In relation to the general welding standard GB/T 50661-2011 (Code for Welding of Steel Structures) and NB/T 47014 (Welding Procedure Qualification for Pressure Equipment), this standard takes precedence for crane steel structure welding, while general requirements not specified herein are implemented per GB/T 50661. The standard classifies weld seams in crane steel structures into three levels based on criticality: Level 1 welds — joints that directly affect safety, such as main girder butt welds, T-joints between flange plates and web plates, and hook beam welds; Level 2 welds — primary load-carrying joints, such as fillet welds connecting stiffening plates to web plates and end carriage connection welds; and Level 3 welds — general structural welds.

Welding Consumable Selection

The standard specifies that welding consumables (electrodes, wires, fluxes, and shielding gases) shall be selected on the principle of equal-strength or under-matching strength:

Shielded Metal Arc Welding (SMAW) — For Q235B (≈S235JR) steel, use E43-series electrodes (e.g., E4303, E4315); for Q355B (≈S355JR) steel, use E50-series electrodes (e.g., E5003, E5015). Basic (low-hydrogen) electrodes such as E5015 must be dried before use per the manufacturer's manual (350–400°C for 1 h) and then kept in a portable heated electrode oven for immediate use. Rutile (acidic) electrodes such as E4303 shall be dried at 150°C for 1 h. Electrodes exposed to ambient air for more than 4 h must be re-dried (no more than two re-drying cycles).

Submerged Arc Welding (SAW) — Q235B is welded with H08A wire + HJ431 flux; Q355B with H08MnA wire + HJ431 flux. Flux must be dried before use (250–300°C for 2 h). Wire shall be free from corrosion and oil contamination.

Gas-Shielded Welding — For CO₂ gas-shielded welding, use ER50-6 wire (Φ1.0–1.6 mm) with CO₂ gas purity of no less than 99.5%. Mixed-gas shielded welding (80% Ar + 20% CO₂) is applicable to critical welds, reducing spatter and improving bead profile. Shielding gas flow rate shall be 15–25 L/min; when wind speed exceeds 2 m/s, windbreaks must be provided.

Welded Joint Design and Groove Types

The standard sets out clear requirements for the design of typical welded joints in crane steel structures:

Butt Joints — Splice butt welds in main girder flange plates and web plates shall be designed as full-strength butt welds, with groove type selected based on plate thickness: I-groove for plate thickness ≤ 8 mm (root gap 1–3 mm); V-groove for 8–20 mm (groove angle 60° ± 5°, root face 1–2 mm); X-groove for 20–40 mm (double-sided welding to minimize deformation); U-groove for plate thickness > 40 mm (to ensure full root penetration). Reinforcement of butt welds shall be controlled within 0–3 mm; excessive reinforcement must be ground flush.

T-Joints — The T-joint between the main girder web plate and flange plate is one of the most critical welds in overhead and gantry cranes. For main girders with Work Duty of A5 and Above, deep-penetration fillet welds or grooved fillet welds shall be used, with leg length no less than 0.7 times the web plate thickness. When web plate thickness is ≥ 12 mm, a single-sided or double-sided groove (groove depth ≥ 4 mm) shall be prepared to ensure full root penetration. The effective throat thickness of T-joints shall not be less than the design value.

Corner Joints and Lap Joints — For fillet welds connecting stiffening plates to web plates, the leg length shall be 0.5–0.7 times the web plate thickness (minimum 4 mm). The overlap length of lap joints shall be no less than 5 times the thickness of the thinner plate. Fillet weld ends shall be wrapped around the corner (wrap-around welding), with a wrap length no less than 2 times the leg length.

Welding Process Control

The standard imposes quantitative requirements for controlling key parameters during the welding process:

Preheating and Interpass Temperature — Preheating is mandatory when the base metal thickness is ≥40 mm or when the ambient temperature falls below 0°C. Recommended preheating temperatures: Q235B (≈S235JR) at 80–120°C, Q355B (≈S355JR) at 100–150°C, and Q420 at 120–180°C. The interpass temperature — measured on the base metal between adjacent weld passes — must not drop below the preheating temperature and must not exceed 230°C. Preheating coverage extends 100 mm on each side of the weld seam. Temperature verification is performed with a surface thermometer (infrared or contact type) at a distance of 50 mm from the weld.

Welding Heat Input — Heat input is calculated as Q = U·I/v, where U is voltage (V), I is current (A), and v is welding speed (cm/min). Insufficient heat input can produce hardened microstructures, increasing the risk of cold cracking, while excessive heat input degrades weld toughness. Recommended heat input ranges for common processes: Submerged Arc Welding at 20–45 kJ/cm, CO₂ gas-shielded welding at 10–25 kJ/cm, and shielded metal arc welding at 10–20 kJ/cm. Final values are established through the Welding Procedure Qualification Record (WPQR).

Welding Sequence — The main girder welding sequence is designed to minimize welding distortion: first weld the fillet welds between the web plate and the bottom flange plate (inducing the desired pre-camber), then weld the fillet welds between the web and the top flange plate, and finally weld the internal stiffening plates. Use backstep welding (with segments of 300–500 mm) or skip welding to distribute heat input evenly. For box girders, the four longitudinal fillet welds must be executed symmetrically by two welders working in tandem.

Post-Weld Hydrogen Release Treatment — For high-strength steel welds with plate thickness ≥60 mm, a post-weld hydrogen release treatment (holding at 200–250°C for 2–4 hours followed by slow cooling) must be applied immediately after welding to prevent cold cracking.

Weld Quality Acceptance and Defect Assessment

This standard defines the acceptance grades and defect assessment criteria for weld quality:

Visual Inspection — All welds must undergo 100% visual inspection. Acceptance criteria: the weld surface must be free of cracks, lack of fusion, weld buildup, and undercut (undercut depth ≤0.3mm for Grade I welds, ≤0.5mm for Grade II, and ≤0.8mm for Grade III). No surface porosity is permitted on Grade I and Grade II welds; Grade III welds may have no more than 3 pores per 100mm of weld length, each with a diameter ≤1.5mm. Overall weld dimensions must be within ±2mm of the design dimensions.

Non-Destructive Testing — Grade I welds require 100% Ultrasonic Testing (UT) plus 10% Radiographic Testing (RT) as verification; Grade II welds require 100% UT; Grade III welds require visual inspection only. UT acceptance is assessed per GB/T 11345: Grade I welds must meet Grade II acceptance (no linear defects), and Grade II welds must also meet Grade II acceptance. RT acceptance is assessed per GB/T 3323: Grade I welds must meet Grade II acceptance, and Grade II welds must meet Grade III acceptance.

Mechanical Properties — Performance requirements for Welding Procedure Qualification Record (WPQR) test plates: tensile strength must not fall below the lower specification bound (LSB) of the base metal's characteristic value; bending test (d=4a, 180°) must show no cracks; impact energy KV₂ (-20°C) must be no less than 27J (Grade I welds) or 20J (Grade II welds). Metallographic examination: no cracks, no lack of fusion, no slag inclusion, and porosity rate not exceeding 2%.

Defect Rework — Non-conforming welds may be reworked, but no more than twice at the same location. Before rework, the defect must be completely removed (by carbon arc gouging or grinding) and verified. After rework, the area must be re-tested by UT and a rework record documented. A second rework requires approval from the technical manager. Kelude Heavy Industry's Welding Workshop strictly implements this standard, maintaining a first-pass yield of welds above 96% for all Grade I welds.

Steel Structure Welding Parameter Comparison Table

The comparison table below outlines the core parameter configuration for steel structure welding, serving as a reference for equipment selection and operational use.

Frequently Asked Questions