GB/T 30025-2013 Crane Steel Structure Standard

GB/T 30025-2013 serves as the foundational standard for the manufacturing, inspection, and acceptance of crane steel structures, covering the entire process from material verification, cutting and forming, welding and assembly, to coating and final acceptance. As the skeleton of a crane, the steel structure's manufacturing quality directly determines the machine's load-bearing capacity and service life. This article provides a systematic review and interpretation of the standard's key provisions.

Scope of Application and Manufacturing Workflow

GB/T 30025-2013 refines and supplements the steel structure manufacturing requirements set out in GB/T 3811 Crane Design Standard. It applies to the manufacture and inspection of primary load-bearing structural members of cranes — main girders, end carriages, outriggers, booms, tower masts, slewing platforms, underframes, and similar components. The standard covers the complete manufacturing flow from incoming raw material to finished product: material inspection → leveling → surface pretreatment → cutting → edge preparation → forming → assembly → welding → post-weld treatment → straightening → machining → final assembly → coating → inspection and acceptance. Each operation is governed by detailed quality control requirements and technical parameters. The standard does not apply to the repair or retrofit of existing crane steel structures, although its technical requirements may be referenced for such work.

Material Requirements and Verification Testing

Steel used in structural fabrication must conform to the design drawings and be accompanied by a certificate of quality from the mill. The standard sets out explicit requirements for material management:

Steel Verification Testing — Verification testing of steel is required under the following circumstances: 1) imported steel; 2) mixed mill lots or incomplete certificates of quality; 3) structural members with design-specified verification requirements (e.g., main girders of cranes with a work duty classification of A6 and above); and 4) steel grades being used for the first time. Verification tests include chemical composition analysis, mechanical property testing (yield strength, tensile strength, elongation, and impact energy), and process performance testing (bending test).

Steel Surface Pretreatment — Prior to cutting, steel must undergo surface pretreatment to remove mill scale, rust, oil, and other contaminants. Shot blasting or shot peening is the recommended method, achieving a surface cleanliness rating of Sa2½ and a surface roughness Rz of 40–80 μm. A shop primer (15–25 μm thick) should be applied immediately after pretreatment to prevent re-corrosion.

Material Substitution — Where procurement constraints necessitate a steel substitution, the replacement material must have mechanical properties and chemical composition at least equivalent to the originally specified steel. When high-strength steel is substituted for standard steel, a structural strength verification must be re-performed and written approval obtained from the design personnel. The weldability of the substitute steel must be validated through a welding procedure qualification.

Cutting and Forming Operations

The standard provides detailed requirements for steel cutting and forming:

Cutting Methods — Steel plates for primary load-bearing structures should be cut using CNC flame cutting or plasma cutting; plates with a thickness of ≤14mm may be sheared. Cut edges must be free of cracks, slag buildup, and heavy dross. Surface roughness of cut edges must not exceed Ra 100 μm. For critical components (main girder web plates and flange plates), cut edges must be machined to remove the hardened layer, which should not exceed 2 mm in depth.

Edge Preparation — Weld grooves must be prepared by machining (edge planing, edge milling, or carbon arc gouging followed by grinding). Groove angle tolerance is ±2.5°, and root face tolerance is ±1 mm. Grooves for critical butt welds must undergo magnetic particle inspection (MPI) prior to welding to confirm the absence of cracks.

Forming Operations — The minimum bending radius for cold-formed steel plates is 16 times the plate thickness (when bending perpendicular to the rolling direction) or 24 times the plate thickness (when bending parallel to the rolling direction). Hot forming must be performed within a temperature range of 900–1050°C, with the final bending temperature not lower than 700°C. Forming accuracy for U-ribs and T-ribs: angular deviation no greater than ±2°, and straightness deviation no greater than 1.5 mm per meter.

Hole Drilling — Holes for bolted connections must be drilled to H14 accuracy, with a hole wall surface roughness of Ra ≤ 25 μm. Holes in high-strength bolt connection plates must be drilled using CNC or template drilling, with a hole diameter tolerance of ±0.3 mm and a hole spacing tolerance of ±0.5 mm. When field-drilling through multiple plies, the plates must be securely clamped together.

Welding and Assembly Requirements

Welding is the core operation in steel structure fabrication, and the standard imposes stringent quality requirements:

Welding Procedure Qualification — Welding procedure qualification (WPS/PQR) is mandatory for any new combination of base material, welding consumable, or welding process. Qualification testing includes joint tensile tests, bending tests, impact tests, and macroscopic metallographic examination. The scope of coverage for welding procedure qualification shall comply with NB/T 47014.

Welder Qualification — Welders engaged in crane steel structure welding must hold a valid welder qualification certificate. The welding tasks performed must correspond to the test items listed on the certificate. Critical welds — including butt welds on the top and bottom flange plates of main girders, T-joint welds between web plates and flange plates, and primary welds on outriggers — must be executed by welders holding a Class II certificate or above.

Welding Sequence — The main girder welding shall follow the principles of symmetrical welding and backstep welding. Weld the fillet welds between the web plate and the bottom flange first, then those between the web plate and the top flange, and finally the welds for the internal stiffening plates. During welding, the heat input must be controlled (Q≤35kJ/cm) to prevent overheating-induced embrittlement in the weld zone. For multi-pass welding, the interpass temperature shall be maintained between 100–200°C.

Post-Weld Treatment — After welding, a visual inspection of the weld seams shall be carried out to check for surface defects such as cracks, undercut, porosity, and slag inclusion. Non-destructive testing (NDT) of critical welds shall be performed no earlier than 24 hours after welding. For butt welds on main girders classified as A5 work duty and above, 100% Ultrasonic Testing (UT) and 10% Radiographic Testing (RT) verification are mandatory.

Straightening, Coating & Factory Acceptance

Post-Weld Straightening — Welding distortion can be corrected using mechanical straightening (press machine) or flame straightening. For flame straightening, the heating temperature must be controlled within 600–800°C (dark red to cherry red) and must never exceed 900°C (overheating). The same area may undergo flame straightening no more than twice. After straightening, the flatness of the main girder web plate must not exceed 2 mm per meter, and the flange plate flatness must not exceed 1.5 mm per meter.

Coating / Painting — The steel structure must be coated within 24 hours after surface treatment, with the interval between coats determined by the coating manufacturer's manual. The recommended primer is Epoxy Zinc-Rich Primer (zinc content ≥ 70%), the intermediate coat should be epoxy micaceous iron oxide paint, and the topcoat should be polyurethane or Acrylic Topcoat. The total Dry Film Thickness (DFT) on the main structural components must be ≥ 80 μm for indoor use or ≥ 120 μm for outdoor use. Surfaces for friction-type High-Strength Bolt connections and Conductor Rail mounting areas must not be painted.

Factory Acceptance Test — The manufacturing process of each crane's steel structural components must produce complete quality records, including: material warranty certificates and retest reports, cutting dimension records, Welding Procedure Qualification Records (PQR), welder qualification certificates, non-destructive testing reports of weld seams, structural dimension inspection reports, Camber measurement records, and coating inspection reports. These records must be retained at least until the crane is scrapped. Kelude Heavy Industry strictly implements every process requirement of GB/T 30025-2013. Before delivery, all main girders undergo a Static Load Test at 150% of the rated load and a Dynamic Load Test at 110% of the rated load.

Crane Steel Structure Manufacturing Inspection Checklist

The comparison table below outlines the core parameters and configurations for crane steel structure manufacturing inspection, serving as a reference for selection and operational personnel.

Frequently Asked Questions