4.6　Inspection of Pipes after Factory Prefabrication

4.6.1　According to the 3D piping diagram,the pipe assembly number shall be inspected one by one.The inside diameter,outside diameter,wall thickness,length,groove,stubtube position as well as its aperture,fixture block shall be re-inspected and recorded.

4.6.2　The elbows and angle of bends,radius of bends,pipe end verticality,back profile reduction rate,wall thickness,roundness and length shall be reinspected and recorded.The following requirements shall be met.

1　The deviation of pipe end verticality is shown in Figure 4.6.2-1.The geometrical deviation of elbows is shown in Figure 4.6.2-2.The plane deviation of elbows is shown in Figure 4.6.2-3.The allowable deviation shall meet the requirements of Table 4.6.2-1.

2　The plane deviation of Π-shape bends is shown in Figure 4.6.2-4.The allowable deviation shall meet the requirements of Figure 4.6.2-2.

Figure 4.6.2-1　Deviation of pipe end verticality

Figure 4.6.2-2　Geometrical deviation of elbows

Figure 4.6.2-3　Plane deviation of elbows

Figure 4.6.2-4　Plane deviation of Π-shape elbows

Table 4.6.2-1　Allowable values of pipe end verticality deviation and elbows geometrical and plane deviation　Unit:mm

Table 4.6.2-2　Allowable deviation of Π-shape elbow planenessUnit:mm

3　Wave degree of hot bending shall be less than 2%,and wave degree of cold bending shall be less than 3%.The ratio between wave pitch A and wave height h shall be larger than 12(see Figure 4.6.2-5).

Figure 4.6.2-5　Elbow wave degree

4　The roundness of hot bending shall be smaller than 7%,and the roundness of cold bending shall be smaller than 8%.For main steam pipes,reheated steam pipes and the pipes with the design pressure greater than 8MPa,the elbow roundness shall be smaller than 5%.The roundness of straight pipe end at the two sides of elbows shall meet the requirements of relative steel pipe technical standard.

5　After bending,the allowable deviation of the angle shall be±0.5°.

6　The actual wall thickness of the elbow outer curve shall not be smaller than the minimum wall thickness of straight pipes.

4.6.3　The dimension of the tee shall meet the following requirements.

1　The verticality tolerance of branch pipesΔf shall be smaller than 1% of the height H of the branch pipes and no greater than 3mm,see Figure 4.6.3(a).

2　Each end face verticality toleranceΔf(see Figure 4.6.3(b))shall meet the requirements of Table 4.6.2-1.

Figure 4.6.3　Branch pipes of tee and end face verticality tolerance

4.6.4　The inside of pipe components shall be kept clean.The outer surface and grooves shall undergo anti-rust treatment.The temporary plugging shall be intact.