System Boundary Determination

DOE-STD-1052-93

7.3.1

Using a copy of the single-line schematic drawings and the piping and

instrument drawings (P&ID) of the selected system, define the system

boundaries as follows:

7.3.1.1

Draw boundary lines such that controlled components and their

associated controllers and instrumentation are within the system

boundary.

7.3.1.2

Piping boundaries for a system should be drawn at a valve, with

the valve included if its function is for isolation of the system.

7.3.1.3

Air-operated valves should include the instrument air system

back to the first isolation valve off the instrument air header and

the local instrumentation (e.g., positioners, current-to--

pneumatic converter and solenoid valves). For the instrument

air system, the valves, regulators, and piping serve the same

function and should be analyzed as part of the instrument air

system.

7.3.1.4

Multiple trains in a system or redundant components within a

system should be included within the same system boundary.

7.3.1.5

When a system contains a heat exchanger, the heat exchanger

should be included with the system that is being cooled.

7.3.1.6

Specific components that are dedicated to a particular system

should be included within that system boundary. For example,

the level and flow instrumentation in the main steam system that

provides signals only to the feedwater control logic should be

included in the feedwater system and not in the main steam

system.

7.3.2

There are some special boundary points that may need to be established. For

example, in order to define functions where control logic is involved, the

analyst may find it convenient to extend a system boundary beyond that

shown on a given drawing to include instrument sensors that drive the system

logic. It should be recognized that system drawings are sometimes not

sufficient to show instrumentation logic and electrical boundaries.

7.3.3

It may be helpful to color code the P&IDs to show the boundaries and each

component that should be addressed in the enhancement effort. In addition,

it also may be helpful to develop a list of components within the boundary to

track their analysis.

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