<p>c, available acid reagent test, 30 seconds after the material 304 does not change color, 201 becomes black; d, bulk samples can be taken to the national authoritative testing center for testing Ingredient assay. 3, watch the outer surface and the tube wall color is smooth and light, the thickness is uniform or rough phenomenon. The general inspection of the basic pipe without this, and the seamless steel pipe is </p>
<p>the use of cold-drawn or hot-rolled production, improper operation in the production process prone to uneven thickness, the pipe surface cracks, etc., and the surface roughness is generally seamless Not polished, if no special requirements on the appearance does not affect the use. 4, the purchase should be selected by the Quality and Technical Supervision assessed outstanding products. There is a long-</p>
<p>term use of testimonials and good word-of-mouth among customers is the most direct and effective way to buy. 5, the rolling pipe often appear within the heavy skin, pitting, and rolling green, under normal circumstances these can not be avoided, but also does not affect the basic use, but the purchase must be selected as little as possible, especially the inspection The inner surface. 6, we must choose the big </p>
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