GB 3087 Grade 20 Seamless Boiler Tubes Standard:GB 3087——Seamless steel pipe for low and medium pressure boilers GB 3087 standard is applicable to the manufacture of high-quality carbon structural steel hot-rolled (extruded, expanded) and cold drawn (rolled) seamless steel tubes for various structural low-pressure and medium-pressure boilers and locomotive boilers.   GB 3087 Grade 20 Seamless Boiler Tubes Quick Details Manufacture:Seamless process ,Hot-finished or Cold-finished Wall thickness(WT): 3.2 mm——21 mm. Outer diameter (OD): 33 mm——323 mm Length: 6M or specified length as required. Ends: Plain End, Beveled End, Treaded   Manufacturing methods of GB 3087 Grade 20 Seamless Boiler Tubes (1)Method of manufacturing steel Steel are manufactured by electric furnace, oxygen converter or open hearth method. (2)Manufacturing method of tube blank The tube blank can be produced by a hot rolling method, and a continuous casting billet or a steel ingot can also be used. (3)Manufacturing method of steel pipe The steel pipe can be manufactured by a hot rolling (extrusion, expansion) or cold drawing (rolling) seamless method.   Chemical composition of GB 3087 Grade 20 Seamless Boiler Tubes

Grade	Chemical Composition(%)
	C	Si	Mn	P	S	Cr	Cu	Ni
20	0.17～0.23	0.17～0.37	0.38～0.65	≤0.030	≤0.030	0.3～0.65	≤0.25	≤0.30

  Mechanical properties of GB 3087 Grade 20 Seamless Boiler Tubes

Grade	Wall thickness (mm)	Tensile strength (MPa)	Yield Strength (MPa)	Elongation %
			≥
20	＜15	410～550	245	20
	≥15		225

  Allowable deviation of outer diameter and wall thickness

Type of steel pipe	Outer diameter(mm)		Tolerance
			ordinary	advanced
Hot rolled tube	OD	≤159	±10%（min±0.50mm）	±0.75%(min±0.40mm)
		＞159	±1.0%	±0.90%
	WT	≤20	＋15.0%(min＋0.45mm) －12.5% －0.35mm)	±10%（min±0.30mm)
		＞20	±12.5%	±10%
		OD≥351	±15%
Cold drawn tube	OD	10～30	±0.40mm	±0.20mm
		＞30～50	±0.45mm	±0.25mm
		＞50	±1.0%	±0.75%
	WT	1.5～3.0	+15% -10%	±10%
		＞3.0	+12.5% -10%	±10%

  Testings (1)Hydraulic test The steel pipe should be hydraulically tested one by one. (2)Flattening test Steel pipes with an outer diameter of more than 22mm to 400mm and a wall thickness of not more than 10mm shall be subjected to a flattening test. (3)Flaring test The steel pipe with a wall thickness of not more than 8 mm can be subjected to a flare test with a top taper of 30°, 45° or 60°. (4) Bending test Steel pipes with an outer diameter of not more than 22 mm will be subjected to a bending test (5)Non-destructive testing According to the requirements of the purchaser, the steel pipe will be ultrasonically tested one by one.   Surface quality of GB 3087 Grade 20 Seamless Boiler Tubes The inner and outer surfaces of the steel pipe do not have cracks, folds, creases, crusting or separation, and these defects should be completely removed. The clearance depth shall not exceed the negative deviation of the nominal wall thickness, and the actual wall thickness at the cleaning site shall not be less than the minimum allowed by the wall.