Dear Members,

I request you to provide the suggestion for the below query,

In a project of underground pipeline 18" API5LX65 with yield value of 445 Mpa as per B31.8, in one area there is a huge drop of 12 meter for a horizontal distance of 65 meter. The pipeline was buried with a post padding of 150mm (i.e. covered with sand of 150mm)initially. But due to natural calamity of rain, the sand above and below the pipeline was washed away and there is no support in the pipeline for a span of 65 meter since the pipeline is rest on rock. So to qualify the affected pipe stress analysis was done by the consultant and they conclude the result as "Even the deflection of the pipeline is about 600mm but the stresses are within the limit, hence the pipe is acceptable",

In this case, the pipeline is analysed as above ground with allowable of 0.75 of yield stress.

My suggestion is, even the stresses are within the limit, the deflection is too high of 600mm, hence the pipeline shall not be qualified.

This query is also connected with the software used (Caesar-II), i.e. my suggestion is even the software shows the stresses are within the allowable limit but in practical case for deflection of 600mm is not acceptable. But the consultant says if the software shows the stresses are ok then it is acceptable.

Please place your suggestions.