生产无缝异型钢管所用的坯料，叫做管坯，合格的管坯是无缝异型钢管生产的先决条件。由于斜轧穿孔的变形特点，对管坯质量（尤其是表面质量）提出了以下严格的技术要求：
The blank used to produce seamless special-shaped steel pipe is called tube blank. Qualified tube blank is a prerequisite for the production of seamless special-shaped steel pipe. Due to the deformation characteristics of cross-rolling piercing, the following strict technical requirements are put forward for the quality of billet (especially the surface quality): （一）管坯直径过大或椭圆度过大，会使无缝异型钢管穿孔时咬入条件变坏，还会因管坯直径压缩量过大而促使内折的发生；
(1) If the diameter of billet is too large or the ellipticity is too large, the biting condition of seamless special-shaped steel pipe will be worsened when it is perforated, and the internal folding will occur because of the excessive compression of the diameter of billet;
（二）管坯的表面质量十分重要，因为在管坯赴任何残障都市带到制品无缝异型钢管上，并且有残障的地点频频会酿成应力集中，通过塑性变形将使残障加深、加长；
(2) The surface quality of the billet is very important, because the billet is brought to the seamless special-shaped steel pipe in any disabled city, and the place where the billet is disabled often results in stress concentration, which will deepen and lengthen the disability through plastic deformation.
（三）内部组织紧要是指缩孔和中央疏松，非金属夹杂的积累、气体的含量等。这种要求的严格程度，随无缝异型钢管的用途和钢种的差异而异；
(three) internal organization is closely related to shrinkage porosity and central porosity, accumulation of non-metallic inclusions, and gas content. The strictness of this requirement varies with the use of seamless profiled steel pipe and the difference of steel grades.
（四）要对无缝异型钢管坯进行显微组织的检验，以测定非金属夹杂物（如硫化物、氧化物及碳化物）的含量及分布形态，鉴别带状组织与脱碳层等；
(4) The microstructures of seamless special-shaped steel tube blanks should be examined to determine the content and distribution of non-metallic inclusions (such as sulphides, oxides and carbides), and to identify the banded structure and decarbonization layer.
（五）为了担保穿孔过程的合理进行和获得高质量的无缝异型钢管，必需对管坯的几何尺寸，低倍组织和表面状态等提出严格的要求；
(5) In order to ensure the reasonable piercing process and obtain high quality seamless special-shaped steel tubes, strict requirements must be put forward on the geometric size, macrostructure and surface state of the billet.
（六）无缝异型钢管坯的低倍组织不应有肉眼可见≥1级的残余缩孔、翻皮、分层、气泡、砂眼、非金属夹杂、白点及裂纹等。
(6) The macrostructure of the seamless special-shaped steel tube blank should not be visible to the naked eye as residual shrinkage, skin turning, delamination, bubbles, sand holes, non-metallic inclusions, white spots and cracks, etc.
