Hydrocarbon Processing - November 2021 - 24

Process Control, Instrumentation and Automation
furnished by the licensor or
engineering for all tags but
are to be generated by the
operating company itself. It
is possible that a tag may fall
into two or more types.
b. Boundary levels: Type of
boundary levels (e.g., H, L,
HH, LL), sometimes called
a standard boundary and
critical boundary. Based on the
company's alarm philosophy,
the number of boundary
levels and names may change.
Every tag that has a defined
boundary level has an alarm
configured on the DCS. This
information comes from
P&IDs and vendor manuals.
c. Data type: Continuous or
discrete-in most cases this
would be continuous, except
in cases where the system data
collection has a time interval
that is significantly high that the
data type may be considered
as discrete. The quality
parameter values obtained
from sampling and laboratory
analysis at certain intervals
can be considered as discrete.
d. Alarm priority: The alarm
priority P1, P2 or P3, as
defined in a company's alarm
philosophy document.
e. Mode of operations: Applicable
mode of operation.
f. Limits: The limiting values
and the units of measurement.
Depending on the mode
of operations and the
boundary type, the actual
limit values may change.
g. Transmitter range and least
count: The maximum/
minimum range and least
count of the transmitter
or measurement gauge.
Note: Data for b, d, e, f and g should
come from alarm rationalization work
(refer to the section below); data for item
c comes from control system engineering
documents; and item g comes from the
maintenance management system or asset
register.
It is advantageous for the operator to
enrich the master data set with more relevant
information, including the level of
risk (e.g., high, medium, low) associated
with each tag. This should be done in line
with the company's risk assessment process.
The licensor or equipment vendor
may not provide this information, and it
will have to be generated by the company
itself. Another set of data that should be
included are concerned with troubleshooting
steps; sometimes called " operator
guide, " as follows:
1. Purpose: Why the measurement
point is on the P&ID.
2. Cause: Why the measured
value may deviate from normal
allowed operating limits
(several reasons exist why the
deviation may occur in normal
circumstances; all known
causes should be listed here).
3. Consequences: The
consequences if operations
are continued for a prolonged
duration (both the activation
of the next level of barrier and
the eventual consequence
may be described here).
4. Actions required to normalize:
This set of actions is listed in
sequential order along with
checkpoints. Operators should
progress through these actions
in given order to normalize plant
operations. Different sets of
actions are for different causes,
so operators must first ascertain
the causes before proceeding.
5. Time required to normalize:
Minimum time required to
complete operator actions
and allow the process
system to recover.
6. Time allowed in deviations:
Maximum time allowed in
deviation-in some cases, this is
relevant for every deviation, while
the cumulative time in deviations
from the last outage or last
inspection would be meaningful.
Both the limit itself and the
allowed time in deviation depend
greatly on equipment metallurgy,
design rating, mode of operation,
sampling locations and frequency
of sampling analysis, inspection
locations and frequencies,
the age of the plant, etc.
7. Responsibility: Person or role
responsible for maintaining
the measured value within
the range, otherwise the same
should be escalated for further
troubleshooting at the subject
matter expert (SME) level.
8. Owner/accountable party: The
SME in the technical hierarchy
who makes sure that the limits
and all other information
remain correct and relevant.
Note: High-quality content is a demonstration
of operational excellence and
the deployment of best practices. Content
is updated each time an abnormal
situation is encountered and the normal
situation is restored.
Alarm rationalization. Most of the required
information and details should be
FIG. 1. A typical consideration for fixing the standard high and low limits for a furnace feed flow.
Various considerations have their own minimum/maximum limits.
24 NOVEMBER 2021 | HydrocarbonProcessing.com
generated by a cross-functional team in
a working session called alarm rationalization
(AR.) The AR exercise is highly
productive if participants include experienced
panel operators, engineers from
operations, process engineers or technical

http://www.HydrocarbonProcessing.com

Hydrocarbon Processing - November 2021

Table of Contents for the Digital Edition of Hydrocarbon Processing - November 2021