Historically, the management of Dead Legs on an installation has been problematic primarily because of the large numbers of Dead Legs that usually exist. This article describes a high-level dead leg integrity management program overview and is based on experience, knowledge and adaptation of inspection management philosophies currently being implemented within the Oil & Gas and the petrochemical industry. The requirements and philosophy described herein serve to provide a systematic approach upon which future inspection and maintenance requirements can be developed, planned and implemented (e.g., life cycle replacement periods, repair scopes, inspection frequencies, scopes and techniques to be employed).
Dead legs can be defined as locations in piping circuits containing idle, stagnant or intermittently flowing fluids. Corrosion in dead legs represents a significant threat to the integrity of hydrocarbon production facilities. High rates of degradation are readily observable at susceptible locations, where corrosion rates of millimeters per year are possible.
This article describes how degradation at dead legs can be prevented. In addition, it provides the mechanisms by which the threat from dead leg corrosion may be assessed in order to develop and establish a written scheme for examination, if prevention is not possible and/or practicable.
API 581 defines “Dead Leg” as a section of piping or piping circuit that is used only during intermittent service such as start-ups, shutdowns, or regeneration cycles rather than continuous service.
API 574 defines “Dead Leg” as components of a piping system that normally have no significant flow. Dead-leg locations include: blanked branches, lines with normally closed block valves, lines which have one end blanked, pressurized dummy support legs, stagnant control valve bypass piping, spare pump piping, level bridles, relief valve inlet and outlet header piping, pump trim bypass lines, high point vents, sample points, drains, bleeders, and instrument connections.