[Haichuan EPC] Do you know what is included in the physical inspection of steel structures?

Weld inspection aims primarily to examine the internal quality and defects of welds, in order to ensure that the structural load-bearing capacity meets the required standards. Ultrasonic non-destructive testing is generally used for this purpose, while radiographic testing is employed in fewer cases. Testing criteria: Code for Acceptance of Construction Quality of Steel Structure Engineering GB 50205-2020, Technical Standard for On-site Testing of Steel Structures GB/T50621-2010, Ultrasonic Testing for Non-destructive Inspection of Welds GB/T11345-2013. Testing items and parameters: Detect internal defects in welds, such as cracks, lack of fusion, incomplete penetration, pores, etc. Sampling frequency: Primary welds shall be sampled at 100%, while secondary welds shall be sampled at no less than 20%, with a minimum of 3 samples. For fully penetrative welds with a plate thickness > 50 mm, add 10% additional radiographic inspection for verification. Number of samples: Take one testing unit for every 100 mm of weld length, with each unit covering at least 3 scanning areas.

Testing of anti-corrosion coatings for steel structures: The testing standards are based on the Code for Acceptance of Construction Quality of Steel Structure Projects GB 50205-2020, the Technical Standards for On-site Testing of Steel Structures GB/T 50621-2010, and the Test Method for Adhesion of Paints and Varnishes by Tensile Method GB/T 5210-2006. Testing items and parameters: coating thickness, adhesion strength, compressive strength, tack, corrosion resistance, weather resistance, hardness, appearance, etc. Sampling frequency: 10% of the number of components of the same type, with a minimum of 3 items ； For every 100 tons used, or less than 100 tons, of thin-coated anti-corrosion paint, the adhesion strength should be tested once; for every 500 tons used, or less than 500 tons, of thick-coated anti-corrosion paint, both the adhesion strength and compressive strength should be tested once. Number of samples: 5 test points per component, with the value for each point being the average of the dry film thicknesses at 3 measurement points spaced 50 mm apart ； Randomly select 20 kg of anti-corrosion paint, and 5 kg of rust-proof paint. Acceptance criteria: The average dry film thickness must be ≥ the design value, and 80% of the measurement points must be ≥ 85% of the design value. When no specific requirements are specified, the dry film thickness outdoors is 150um, and 125um indoors ； The allowable deviation for coating thickness is -25um, and the allowable deviation for each coat of coating is -5um.

Testing of fire-resistant coatings for steel structures: The testing standards are based on GB 50205-2020 \"Code for Acceptance of Construction Quality of Steel Structure Projects\" and GB 14907-2018 \"Fire-resistant Coatings for Steel Structures\". Testing items and parameters: dry film thickness, adhesion strength, fire resistance limit, expansion ratio, weather resistance. Sampling frequency: 10% of the number of components of the same type, with a minimum of 3 items. Number of samples: For determining the thickness of the fire-resistant coating on floors and firewalls, an area formed by the intersection of two adjacent vertical and horizontal axes can be used as a unit; on the diagonal of this area, a point is selected every meter for testing ； The thickness of the fire-resistant coating on the beams and columns of fully steel frame structures is determined by taking samples at intervals of 3 meters along the length of the components for testing ； For truss structures, sections of the top and bottom chords are to be inspected at intervals of 3 meters as specified, while one section each is to be inspected for all other members. Acceptance criteria: The average dry film thickness must be ≥ the design value, and 80% of the measurement points must be ≥ 85% of the design value ； Adhesive strength ≥ 0.15 MPa ； The fire resistance rating meets the design requirements ； The expansion ratio of expansion coatings is ≥5 times.

Inspection of high-strength large hex head bolt assemblies. Inspection standards: GB 50205-2020 \"Code for Acceptance of Construction Quality of Steel Structure Engineering\", GB/T 1231-2006 \"Technical Requirements for High-Strength Large Hex Head Bolts, Large Hex Head Nuts, and Washers Used in Steel Structures\". Testing items and parameters: Torque coefficient of the connection pair. Sampling frequency: Washers of the same manufacturer, furnace number, specification, machining method, heat treatment process, and performance grade are considered to be part of the same batch; bolt-nut-washer assemblies composed of bolts, nuts, and washers from the same batch are regarded as the same batch of assemblies. For bolt assemblies for which the torque coefficient must be guaranteed, the maximum batch size is 3,000 sets. Number of samples: 8 sets of connectors should be sampled from each batch for re-inspection. Each set of coupling components should be tested only once and must not be reused. If the washer rotates during tightening, the coupling components should be replaced and the test repeated.

Detection of the anti-slip coefficient of the friction surfaces in high-strength bolt connections. Standards for detection: GB 50205-2020 \"Code for Acceptance of Construction Quality of Steel Structure Projects\" and GB/T 32270-2015 \"Methods for Detecting the Anti-Slip Coefficient of Friction Surfaces in Steel Structures\". Testing items and parameters: anti-slip coefficient. Sampling frequency: Components of the same material and with the same surface treatment process are considered as one batch; each batch consists of 2000 tons, and amounts less than 2000 tons are also regarded as one batch ； Each surface treatment process is tested separately. Number of samples: 3 sets of spliced specimens are taken per batch, with each set containing 2 friction surfaces. Acceptance criteria: The measured value shall be ≥ the design value; typically, for Q235 steel after sandblasting, μ≥0.40, and for Q355 steel after sandblasting, μ≥0.40, with this value dapat be increased to 0.50 in cases of special designs.

Inspection of torsional shear high-strength bolt connections. Inspection standards: GB 50205-2020 \"Code for Acceptance of Construction Quality of Steel Structure Engineering\" and GB/T 3632-2008 \"Torsional shear high-strength bolt connections for steel structures\". Testing items and parameters: Axial force of the connection fitting fastening. Sampling frequency: Washers made from the same material, with the same furnace number, specifications, machining methods, heat treatment processes, and surface treatment processes are considered to be part of the same batch. Connection assemblies composed of bolts, nuts, and washers from the same batch are regarded as belonging to the same batch as well. The maximum batch size for bolt connection assemblies intended to ensure a consistent torque coefficient is 3,000 sets. Number of samples: 8 sets of connectors should be sampled from each batch for re-inspection. Each set of coupling components should be tested only once and must not be reused. If the washer rotates during tightening, the coupling components should be replaced and the test repeated. Inspection of high-strength bolts used in steel grid shell bolted spherical joints: Inspection standards: GB/T 16939-2016 \"High-strength bolts for steel grid shell bolted spherical joints\" and JGJ7-2010 \"Technical specifications for spatial grid structures\". Testing items and parameters: Actual tensile load (for bolts of M39–M85×4, hardness is used in place of the tensile load). Sampling frequency: Bolts with the same performance grade, material grade, furnace number, specification, machining process, heat treatment process, and surface treatment process are considered to be part of the same batch. The maximum batch size for bolts of M36 or smaller is 5000 pieces, while for those larger than M36, it is 2000 pieces. Number of samples: Minimum number of specimens for tensile testing: 8 bolts ； Fastening axial force/torque coefficient: 8 sets of connections ； Slip amount: 3-node specimen; Acceptance criterion: Minimum actual tensile force ≥ nominal tensile strength ； The tightening axial force meets the design requirements ； Torque coefficient 0.11-0.15 ； Node slip amount < 0.1mm ； The hardness meets the requirements of GB/T 16939 (e.g., grade 10.9 HV324-395).

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