Page 224 - Water Standards
P. 224

Table 4   1   16-2  Allowable misalignment error of the circular seams
                                                             Unit: mm
                    Wall thickness δ              Allowable error

                        δ≤30                  15% δ, and no larger than 3
                       60>δ>30                       10% δ
                        δ≥60                          ≤6
               5  Unless required by the drawings, the circular seams shall be welded one by one in
           sequence or being assembled by force. Components such as temporary supports or pedal plates
           shall not be welded to the pipe wall at will. The circular seams shall not be re⁃welded after
           casting of concrete  
               6  When dismantling the steel pipe fixtures, hoisting eyes, inner supports and other
           temporary components, carbon arc⁃air gouging or an oxygen⁃acetylene flame shall be used in⁃
           stead of hammering to cut these components at a position at least 3mm from the pipe wall,
           and the parent metal shall not be damaged. After dismantling, the residual traces and
           welding scars on the pipe inner wall shall be rubbed down by grinding wheels. The pipe wall
           shall be checked carefully to see if there are any tiny fissures  
               7  After the installation, the steel pipe shall be welded together with the buttress and
           anchor bolts to prevent displacement caused by concrete casting  
               8  For the pipe outer and inner walls, any localised pits whose depths are no larger than
           10% of the wall thickness and no larger than 2mm, may be polished by grinding wheels to
           smoothen the surface. For pits whose depths are larger than 2mm, carbon arc⁃air gouging or
           grinding wheels shall be used to gouge or rub the pits to become grooves which are easy to be
           repaired by welding  
               9  Grouting holes shall be preformed in the manufacturing process. Before the grouting
           hole are plugged and welded, water, cement paste, rust and other waste shall be cleared a⁃
           way. There shall be no water leakage after welding  
               10  During the civil engineering construction and electromechanical installation, no
           component shall be welded to the pipe wall without permission.
           4   1   17  Installation of exposed penstocks shall meet the following requirements:
               1  The top surface camber of saddle⁃type supports shall be checked by regular templates
           and the gap between the surface and the template shall be no larger than 2mm  
               2  For roller type and swing type buttresses, the elevation and lengthwise and crosswise
           centers deviations of the cushion plate shall be no larger than ±5mm. The parallel deviation
           between the steel pipe  s actual and design axes shall be no larger than 2/ 1000. If the drawing
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