scope:

This recommended practice covers the design, execution, inspection, and safety of a pipeline-lowering operation conducted while the pipeline is in service. It presents general guidelines for conducting a pipeline-lowering operation without taking the pipeline out of service. It also presents equations for estimating the lowering-induced stresses. To promote the safety of the lowering operation, it describes stress limits and procedures. It outlines recommendations to protect the pipeline against damage. The practicality and safety of trench types, support systems, and lowering methods are considered. Inspection procedures and limitations are presented.

The calculations in this recommended practice are based on methods developed from elastic free deflection theory to determine lowering-induced stresses and deflection profiles. Other calculation methods such as finite element analysis may instead be used. See the publications listed in 1.7.

Methods for handling field bends, valves, fittings, or other attachments to a pipeline and methods for lowering a pipeline with attached appurtenances are beyond the scope of this recommended practice.