HYDROCARBON
ENGINEERING
44
project was to assess and improve the company’s operational
standards, spurred by what occurred at Buncefield.
Letico, an engineering services firm based in Montreal,
Canada, provides process control and systems integration
solutions in various industrial sectors, including oil and gas.
The oil company held more than a dozen storage terminals
across Canada, with facilities and tanks varying by time of
construction or installation. Their designs dated back to when
equipment was not as advanced, and overfill prevention did
not receive a heightened focus. Given the hazards of
petrochemicals storage, the customer wanted to have an
accurate overview of its overfill protection status and a plan
to improve effectiveness and enterprise-wide consistency of
its own internal standards and engineering practices.
At the project’s outset, and as part of ongoing safety
improvements, Letico and its customer agreed on systems
integration goals:
n
Identify level-related alarm gaps.
n
Establish recommendations to rectify these gaps.
n
Quantify tank level alarm setting at various fuel storage
terminals across Canada.
n
Confirm compliance with corporate engineering practices,
defining the minimum engineering and system
configurations required for storage tank level alarm
systems.
n
Ensure compliance with the requirements for gauging and
independent level alarms for atmospheric tanks (fixed
roofs both with and without IFRs).
n
Consider the recommendations of the Buncefield
Incident Final Report of the Major Incident Investigation
Board, as well as API 2350 Overfill Protection for Storage
Tanks in Petroleum Facilities 4
th
Edition.
n
Modify in-service tanks to comply with API 2350
4
th
Edition.
n
Calibrate ATG systems with reference to the independent
level devices.
Systems integration management
The Letico team managed the project in phases: reporting,
implementation, documentation, and installation/testing. In
the reporting phase, critical initial steps were to audit existing
terminals and tank installations to evaluate overfill prevention
processes and technology.
The company needed to identify if these individual
operating systems were meeting or deviating from internal
engineering standards, and if they would meet industry
standards for safety. At the time, the API was preparing the
API RP 2350 4
th
Edition, but the information was not yet
available when the project was initiated. The plan was to
apply the customer’s internal engineering practices, which
were quite comprehensive and specific, while anticipating the
publication of the 4
th
Edition and its impact on current
standards.
Strategic supply
One of the suppliers being assessed for the project’s level
instrumentation needs, Magnetrol International, was able to
step in and help Letico and its client understand the new
API RP 2350 guidelines, which were imminent at the time.
Magnetrol was represented on the API 2350 publication
committee and shared valuable insight on the forthcoming
recommended practices with Letico’s team. It was able to
prepare, to evaluate, and potentially implement compliance
measures based on the API standard, even while the
company was moving ahead independently of its
publication.
API RP 2350 key points
Applicability
Aboveground storage tanks (ASTs) with capacities
greater than 1320 gal. (5000 l) that store Class I, II or III
flammable or combustible liquids, and that receive
liquids from mainline pipelines or marine vessels.
Management system
API RP 2350 recommends a management system
focused on overfill prevention. This system should
include documented procedures for normal and
abnormal conditions including safety, emergency
response, trained and competent personnel, properly
maintained and tested OPS, management of change
process and incident reporting and investigation.
Independence
A key feature of API RP 2350 is that the sensors and
alarms used for HH tank level or any part of the AOPS
may not be used for routine tank filling operations. In
addition, the HH level sensor on Category 3 tanks must
be independent from all other level sensors.
Required alarms
High-high alarm (Category 2 and 3) and optional
diagnostic alarm (Category 3).
Equipment
Overfill prevention system (OPS) typically includes
an alarm signal system and allied support
systems – shutdown or diversion valves,
communications, sensors, and logic solvers. An OPS
should be on an uninterruptible power supply. Use of
wireless communication is prohibited by API 2350.
Redundancy
A common strategy for critical level detection is
redundancy of the sensors. Ideally, redundant sensors
will be of disparate technologies to avoid multiple
failures due to application concerns.
Proof testing
All OPS equipment required to terminate receipt must
be tested annually. The HH sensor and alarm must be
tested semi-annually. Method of proof testing must
stimulate an overfill situation as closely as possible, but
may not require filling the tank above the maximum
working level. Possible methods are manual testing,
push-button testing, self-diagnostics or devising a wet
probe testing.
Floating roof sensors
A sensor used on a floating roof tank must detect the
roof, as well as the liquid, should it cover the roof.
