GB 6479-2013[GB/T 6479-2013] Seamless steel tubes for high-pressure chemical fertilizer equipment (English PDF)

4.1 Outer-diameter and wall-thickness

4.1.1 The nominal outer-diameter (D) and nominal wall-thickness (S) of steel tubes

shall meet those specified in GB/T 17395.

4.2 Allowable deviation of outer-diameter and wall-thickness

4.2.1 Allowable deviation of outer-diameter and wall-thickness of hot rolled

(squeezed and extended) steel tubes shall be in accordance with those specified in

Table 1.

4.2.2 Allowable deviation of outer-diameter and wall-thickness of cold-drawn (rolled)

steel tube shall meet those specified in Table 2.

4.3 Length

4.3.1 General length

General length of steel tubes is 4000mm ~12000 mm. Based on the agreement of

both Seller and Buyer, the steel tubes longer than 12000mm and the ones with length

between 3000mm and 4000mm may be delivered if indicated in the contract; the

quantity shall not exceed 5% of the total quantity delivered at this batch.

4.3.2 Specified length and multiple length

4.4 Curvature

4.4.1 Curvature per meter of steel tubes shall meet those specified in Table 3.

4.5 Out-of-roundness and wall unevenness

As required by the Buyer, based on the agreement of both Seller and Buyer and also

indicated in the contract, the out-of-roundness and wall unevenness of steel tubes

shall not exceed 80% of the tolerance of outer-diameter and wall-thickness

respectively.

4.6 End shape

The surface of both ends of steel tube shall be vertical to the axis and the cutting burrs

shall be cleared away.

4.7 Delivery weight

5.1 Designation and chemical composition

5.1.1 Designation and chemical composition (melting analysis) of steel shall be in

accordance with those specified in Table 4.The steel tubes are accepted based on

the smelting composition.

5.1.3 If the steel is smelted in oxygen converter, the nitrogen content shall not be

greater than 0.008 % except 12Cr5Mo.

5.1.4 Carbon equivalent (CEV) of Q345B, Q345C, Q345D and Q345E shall not be

greater than 0.45 %. The carbon equivalent shall be analyzed for its composition by

melting and calculated by Equation (1).

CEV=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15... (1)

5.2 Manufacturing method

5.2.1 Manufacturing method of steel

The steel shall be treated by electric arc furnace and external refining with vacuum

refining or oxygen converter and external refining with vacuum refining or smelted by

electroslag remelting process.

5.2.2 Manufacturing method of tube blank

The tube blank may be manufactured by continuous casting, die casting or heat

rolling (forging).

5.2.3 Manufacturing method of steel tubes

The steel tube shall be made with hot rolled (squeezed and extended) or cold-drawn

(rolled) seamless methods. The method designated by the Buyer shall be indicated in

the contract.

5.3 Delivery state

The steel tubes shall be delivered in heat treatment state. The heat treating system

shall be in accordance with those specified in Table 6 and shall be filled in the quality

certificate.

5.4.2 The impact absorbed energy in Table 7 is the required value of Charpy V-notch

of specimen of standard dimension. Where the small-dimension impact specimen is

adopted, the required value for impact absorbed energy of Charpy V-notch shall be

the required impact absorbed energy of specimen of standard dimension multiplied by

the decline factor in Table 8.

5.4.4 The steel tubes with outer-diameter of less than 219 mm shall be sampled

longitudinally along the steel tubes in the tensile test.

5.5 Hydraulic test

5.5.1 The steel tube shall be subjected to the hydraulic test one by one; the test

pressure shall be calculated according to Equation (2). The maximum test pressure is

20MPa; pressure stabilization time is not less than 10s. Under the test pressure, the

steel tube shall be without leakage.

5.6 Processing properties

5.6.1 Flattening test

5.6.1.1 Steel tubes, except 12Cr5Mo steel tube, shall be subjected to flattening test

if outer-diameter is between 22mm ~ 600mm and S/D <= 0.15.

5.8 Nonmetallic inclusion test

5.8.1 Steel tubes directly rolled with continuously cast round billet or steel ingot shall

be subjected to nonmetallic inclusion test which may be rated according to Method A

in GB/T 10561-2005; for class A, class B, class C, class D inclusions, both fine and

thick level shall not be higher than 2.5; DS inclusion shall not be higher than Grade

2.5; the total fine and thick level for class A, class B, class C, class D inclusions shall

not be higher than 6.5 respectively.

5.9 Surface quality

5.9.1 There shall not be crack, wrinkles, creasing, delamination or scabs on internal

and external surfaces of steel tube. All these defects shall be cleared away and

clean-up depth shall not exceed negative deviation of nominal wall-thickness. The

actual wall-thickness on the cleaning places shall not be less than the permissible

minimum value of wall-thickness.

5.10 Nondestructive examination

5.10.1 Steel tube shall be subjected to ultrasonic inspection examination one by one

according to GB/T 5777-2008.The longitudinal slot depth of contrast tubes follows L2

for cold-drawn (rolled) steel tubes or L2.5 for hot-rolled (squeeze and extended) ones.

6.1 The dimension and shape of steel tube shall be measured by the measuring tool

in conformity with accuracy requirement.

6.2 Internal and external surfaces of steel tube shall be subjected to visible

examination in the abundant illuminating condition.

7.1 Inspection and acceptance

The inspection and acceptance for steel tube shall be carried out by the quality and

technical supervision department of the Seller.

7.2 Batching rules

Steel tubes shall be inspected and accepted based on the smelting furnace for

chemical composition, macroscopic examination and nonmetallic inclusion test; the

rest inspection items shall be inspected and accepted according to batches.

7.3 Sampling quantity

Sampling quantity of each batch of steel tubes shall be selected according to those

specified in Table 11 for each examination.