10. The minimum thickness of the bent pipe must not be less than the designed wall thickness of diameter.
11. The center deviation of the pipe end of the elbow shall be in accordance with the following regulations:
1） In the GC1 pipeline and the C pipeline for fluid, the elbow whose degree of transmission toxicity is an extremely dangerous medium or whose design pressure is greater than or equal to 10MPa, the center deviation value of each tube end (Figure 2) shall not exceed 1.5mm.When the straight pipe length is more than 3m, the deviation must not exceed 5mm.
2） For other pipe bends, the center deviation of per meter (Figure 2) must not exceed 3mm. When the straight pipe length is more than 3m, the deviation must not exceed 10mm.
1 - Requested center;
2 - Actual center;
L - Straight length of elbow;
- Pipe end (Tube end);
12. The allowable deviation of the flatness for the Π shaped pipe bending (Figure 3) should meet the requirements of Table 3.
L - Straight length of elbow；
Table 3 Flatness tolerances of Π-shaped elbow (mm)
|Straight length L||≤500||>500~1000||>1000~1500||>1500|
13. In GC1 grade pipelines and C class fluid pipelines, after the elbow is made, whose degree of transmission toxicity is an extremely dangerous medium or whose design pressure is greater than or equal to 10MPa, the surface should be checked by non-destructive testing according to the current national standard "Non-destructive testing of pressure equipment" JB/T4730. Heat treatment should be done before non-destructive testing.When there are defects, grinding can be done. The wall thickness of the pipe bending elbow after grinding shall not be less than 90% of the nominal wall thickness of the pipe and shall not be less than the designed wall thickness.
14. After the bent pipe is qualified, it shall fill out the “Processing record of pipe bending” and “Pipeline Heat Treatment Report” respectively. Its format specification shall refer to “Construction standards for industrial metal pipeline project” Table A.0.3 and A.0.4.
A.0.3 The format of processing record for pipe bending
|Project Number||Project Name||Sub-project Name/Number|
|Pipeline NO.||Pipeline Number||Materials||Specification||Bending Radius||Angle or Size Deviation||Roundness||Pleat Height(Fold Height)||Pipe Thickness||Heat Treatment Temperature||Hardness Value HB||Non-destructive Testing Results|
|Sketch and description：|
Engineer： Quality inspector： Construction workers：
A.0.4 Report format of pipeline heat treatment
|Project Number||Project Name|
|Specification||Welding Material Number|
|Heating Rate (℃/h)||Heat Treatment Temperature (℃)||Constant Temperature Time (h)||Cooling Rat (℃/h)|
Heat treatment curve:
(Attachment: automatic recorded heat treatment curve)
15. The Scope
This standard is according to GB/T9711 standards series, in Table 4 specifies three levels of heating bent pipe by steel induction, the base material meets GB/T9711 quality requirements on the basis of technical condition of steel pipe delivery and additional quality requirements.
When the mother material meets the standards of other steel pipes except GB/T9711, the quality requirements and classification methods are agreed by consensus, but the load carrying capacity must be guaranteed.
Table 4 Induction Heating Of Pipe Bending Grades And Related Steel Pipe Standards
|Steel pipe bending grade|
Related steel pipe standards
|Grade B||GB/T9711.2 √|
16. Normative reference documents
The clauses in the following documents have been adopted as references to this standard.For dated reference documents, all subsequent amendments (not including errata content) or revisions do not apply to this standard. However, encourages all parties that reached agreement under this version to use the latest version of these documents. For dated references, the latest edition is applicable to this standard.
GB/T2288; Method for tensile testing at room temperature
GB/T232; Metal Material; Bending test method
GB/T246; Metal tube; Flattening test method
GB/T2358; Test method for crack tip opening displacement of metallic materials
GB/T8923; Corrosion grade and derusting grade of steel surface before painting
GB/T9445; Qualification and certification for non-destructive testing personnel
GB/T11344; Thickness measuring method of contact ultrasonic pulse echo
GB/T18253; Steel and Steel Products; Types of Inspection Documents