The wall thickness of elbow is beyond the standard

Due to the site of the arrival of the The wall thickness of elbow exceeds bid badly, need to be done according to the actual measurement of pipeline stress calculation, the calculation of wall thickness to exceed bid, pipes, pipe stress on device interface thrust and torque is qualified, and whether to set up reasonable pipe rack. In the pipeline stress calculation procedures, bend the wall thickness of the default for the connection pipe wall thickness, calculating the stress strengthening coefficient of elbow and flexible coefficient. To accounting need to select the wall thickness of the pipe connected to the elbow. By the weight of the elbow to convert in this wall thickness, the bend along the centerline and diameter into a straight pipe (straight pipe length equals the bend axis length), the weight unfolds the straight pipe and elbow weight is consistent, the straight tube wall thickness for the bend in the form of weight reduced wall thickness.
The elbow convert of calculated thickness back to piping stress calculation model, can be bend the impact on the pipeline after the wall thickness of paint.
1. The stress influence of the pipes
The wall thickness of elbow change before and after the pipe elbow in a stress and secondary stress calculation results. Elbow bend wall thickness increase after a stress most showed a trend of decrease, and the secondary stress showed a trend of increase, but a change of stress and secondary stress were not more than 20%. According to the specification, in the case of not consider accidental loading, a stress piping shall be conducted by the pipe pressure, gravity and other continuous load. Internal pressure is constant, there is no external load cases, the increase of thickness, stress strengthening coefficient decreases, and will cause the bend of a lower stress. Individual point due to the elbow wall weight increase, reduce the impact of the offset the stress strengthening coefficient, makes a stress rose slightly.
And in the absence of other secondary stress under the influence of cyclic loading is mainly caused by thermal expansion the joint torque generated in the cross section. As a result of the The wall thickness of elbow increases, the bend of the flexible coefficient K value is reduced, makes on the cross section of torque increase, so the secondary stress will increase.
2. The effects on thrust torque device interface
The wall thickness of elbow change push pipe of equipment interface of thrust and torque changes, pipe of high the influence of interface are discussed here.
By the calculation results can be seen that as a result of the The wall thickness of elbow increased, under the thermal state of resultant force and torque will increase, the biggest increase of 52.18%, the smallest is 14.76%. The reason is due to the changes of bend flexible coefficient. Flexible coefficient said bent pipe relative to the straight pipe under the bending moment increase flexible degree, its value is equal to the same deformation conditions, in accordance with the general and the bending moment and bending theory considering the bent pipe cross section to calculate the bending moment of the ratio of flat effect.
3. The impact on pipe, lifting point load
After The wall thickness of elbow change, in the piping of lifting point loading will change too.
By the calculation results can be seen that elastic bearing point of the steam extraction pipeline hot rate reached 15%, and drain piping hot load change rate is not more than 5%, the difference is mainly due to the different piping within the medium. Due to the drain pipe medium is water, bend weight is small, the proportion in the whole piping weight change not for piping lifting point load is too big change. But medium for steam of the steam extraction pipeline, density is small, elbow weight is bigger, the proportion in piping wall thickness change, will cause the tube department bearing load must be changed. But no matter how to load variation, spring support in terms of piping size spring jump phenomenon happens.
Source: Yaang Pipe Industry Co., Limited (www.yaang.com)

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