The raw materials used in building steel structure engineering are divided into main material, auxiliary material and enclosure material, the main material is steel (steel plate, profile and pipe); the auxiliary material is connection material (welding material, bolt, stud, rivet) and coating material (paint and fire retardant coating); the enclosure material is metal molding, metal sandwich plate (including purlin).If the steel structure project is relatively large, the steel can be ordered from the steel plant and rolled in fixed length; for the steel with small consumption or urgent need, it can be purchased directly from the supplier.However, two aspects must be paid attention to when selecting and purchasing steel materials. One is to make every effort to purchase practical steel according to the actual engineering structure, so as to achieve the purpose of reasonable use of materials and reduce cost. When selecting and purchasing steel products, both economy and technical requirements specified in the design should be considered. 

      1、 When purchasing the main materials of steel structure engineering, it is necessary to check the material quality assurance certificate and relevant quality terms, and check the quality certificate and inspection report issued by the steel plant in detail. Its chemical composition, mechanical properties and other relevant quality requirements must comply with the current national standards, and the furnace batch number on the quality certificate shall be consistent with the standard on the steel material.At the same time, check, verify and approve the size and specification of the real objects in the material quality specification, such as thickness and local surface roughness.

     2、 Appearance (VT) quality of steel used in steel structure and relevant requirements.Cracks, scabs, lines, bubbles and inclusions are not allowed on the steel surface.The local unevenness of steel plate surface is within the range of 1000 mm, and the allowable error is 1.0 mm.There should be no delamination and slag inclusion on the steel end face. If the above defects exceed or do not exceed the standard, the treatment results shall be submitted to the relevant parties and suppliers.  

     3、 The re inspection of steel products shall be in accordance with the national standard code for acceptance of construction quality of steel structures (GB 5025-2001). The imported steel products shall be inspected according to the standards of the supplier country or according to the terms of the order contract. Those who fail to pass the commodity inspection shall not be used.For the mixed batch of steel, when the steel is of different strength grade, spectrum or mechanical test shall be carried out one by one to determine the grade.If the thickness of steel plate is equal to or greater than 40 mm, and the design has Z-direction performance requirements, there are professional requirements.The safety level of building steel structure is grade I, and the steel used in the main load-bearing components of long-span steel structure.

     4、 Steel inspection shall be carried out in batches. The weight of each batch of steel from the same steel plant, which is composed of the same brand, the same batch number, the same furnace and tank number, the same processing method, the same quality grade, the same variety, the same thickness and specification and the same delivery status shall not exceed 600t.