The ribben structure existing in water-wall tubes made from carbon steel has been discovered in metallographic test.It is believed from test and example analysis that the ribben structure is a kind of defects.The ribben structure in carbon steel is commonly resulted from composition segragation

the more serious the composition segragation is

the more grave the resulted ribben structure may be

leading to decrease of elongation rate after material breakage

making the boiler tubes to lose efficacy too early.For rifled seamless steel tubes made from high quality carbon steel.only strictly controlling the smelting and rolling processes

a homogeneous ferrite + pearlite structure can be obtained.