11. Alternate Means of Process Overpressure Protection
a. In some situations where there are concerns regarding high flare system loading and
backpressure, vapor velocity and/or flare radiation, an alternative to traditional pressure relief valve
and flare system design that utilizes a highly reliable instrumented isolation or shutdown system may
be considered in process industry.
b. Proactive measures to reduce or eliminate the flare load case(s) shall be identified, evaluated
and, where possible, implemented prior to considering installation of an instrumented protection
system.
11.1 HIPS Prerequisites
If all of the following conditions are met, a HIPS (High Integrity Protective System) may be considered for
installation in a new or existing facility:
a. No proactive measures, including dynamic analysis, are available to reduce the relief load
b. A Cost Benefit Analysis has been performed which indicates that the life cycle cost of installation,
testing and maintaining a HIPS system is less than the life cycle cost of a traditional PSV/Flare system
c. A Fault Tree Analysis (FTA) is performed to verify the Safety Integrity Level (SIL) of the system.
This analysis shall be performed by an expert independent from the project design staff, the operating
plant and the manufacturing company providing the equipment HIPS equipment.
d. The operating facility shall perform the preventative maintenance, testing and follow the
operating procedures, as outlined in the FTA. The process equipment shall be designed to facilitate
the preventative maintenance and testing as outlined in the FTA.
e. It has been recognized that applicable codes and regulations do not adequately cover the use of
a HIPS system. The importance of preventive maintenance, testing, operating procedures and design
requirements identified in the FTA shall be clearly understood and agreed to by the Plant Manager.
11.2 Additional Protection
A PSV designed for fire case is provided to protect each vessel in addition to a HIPS system only if the fire
case is valid.
11.3 Consequences of Failure
The Safety Instrumentation Level (SIL) for each specific HIPS application shall be based on the
consequence of failure of the HIP system, as shown in the following chart:
11.4 Independent Function
A HIPS system shall function independently of the process control system. Equipment components of a
HIPS system shall not be used for process control or any other purpose.
11.5 Fail-Safe Design
The design of the HIPS system shall be fail-safe. Both isolation valves shall close automatically in case of
failure of any part of the system, including:
a. Loss of power to any of the components.
b. Break or rupture of instrument (air) piping or cabling.
c. Loss of a sensor loop.
d. Failure of the logic/control system.
11.6 Response Time
The response time of a HIPS system shall be such that the maximum pressure in any process component
shall not exceed 10 percent of its design pressure.
11.7 Surge Pressures
Surge pressures caused by the rapid closing of HIPS isolation valves shall be taken into account in the
design of both the upstream and downstream piping systems (See ASME B31.3). The extent of the
possible surge pressures shall be estimated from the results of the dynamic simulation or pressure setting
calculation.
11.8 By-Passes
Bypasses around HIPS system isolation valves shall be designated “Locked Closed”, with controls on their
operation consistent with those used for block valves provided for maintenance on relief valves. Operation
of the bypass valves shall be explicitly studied in the reliability analysis.