SUBSEA
Study explores all-electric subsea
HIPPS reliability and maturity
Research indicates that SIL 3 is achievable
Craig W. Lamison
Granherne, a KBR Company
Khalid Mateen
Total
With subsea developments moving to longer tiebacks and eeper water, all-electric architecture has potential ad- vantages over the conventional electro-hydraulic system: lower cost resulting from doing away with the hydraulic umbilical, reduced and easier maintenance, less environmental impact, and simplifcation of topsides. All-electric equipment
is now becoming available for subsea hydrocarbon development activities to allow this.
Use of the all-electrical architecture in developing a high-pressure
feld, however, requires a reliable subsea autonomous all-electric
High Integrity Pressure Protection System (HIPPS), to allow a lower design pressure than the shut-in wellhead pressure for the downstream facilities. This pressure de-rating of infrastructure could allow further cost savings.
Recently, research was undertaken in a DeepStar study to assess
the Safety Integrity Level (SIL) achievable for an all-electric subsea
HIPPS. Where data was scant, due to the immaturity of the technology, the assessment was based on conservative assumptions. The
work showed that an SIL 3 is achievable for an all-electric subsea
HIPPS. This is in the same range as that of electro-hydraulic systems for similar architectures.
The work evaluated the probability of loss of containment in a
HIPPS Utilizing System (HUS) with multiple wells and HIPPS. It covered both electro-hydraulic and all-electric HIPPS based on the probabilities of failure on demand (PFDs) developed in the SIL assessment.
This evaluation determined the probability of loss of containment for
several HUS concepts to identify how the PFDs previously calculated
affect typical subsea tieback designs using multiple HIPPS.
The evaluation showed that common cause failures signifcantly
infuence the probability of loss of containment. Reducing common
cause failures by employing different equipment can reduce the
probability of loss of containment by a factor of two.
As common cause failures are independent of the number of
HIPPS, smaller HIPPS could be used at each well rather than one
large HIPPS at the manifold. The study also found a lack of prototype all-electric actuated valves and associated reliability data at the
higher pressure ratings where HIPPS are most useful.
Although not addressed in detail in this article, the work also
identifed gaps to be addressed to bring all-electric HIPPS technology to the same technology readiness level (TRL) as conventional
electro-hydraulic HIPPS.
A number of industry documents provided guidance. These included API RP 17O, Recommended Practice for Subsea High Integrity Pressure Protection Systems, and API Specifcation 14C, Rec-
All-electric HIPPS service requirements.
Characteristic
Tieback distance to host
Minimum arrival pressure at host
Water depth in field
Clustered producing wells within 100 m radius
Flowline insulation
Flowline pigging
Product type
Gas oil ratio
Product Corrosiveness
Maximum shut in pressure
Minimum pressure
Well head flowing maximum temperature
Valve sizes
Safety Integrity Level (SIL) Category
Value
30 miles
1,500 psig
10,000 ft
4
Yes
Roundtrip
Oil
1700
Sweet
5,000 to 20,000 psi
0 psia
300 °F
5 to 9 in
SIL 3
ommended Practice for Analysis, Design, Installation, and Testing
of Basic Surface Safety Systems for Offshore Production Platforms.
IEC 61508, Parts 1 to 4, Functional safety of electrical/electronic/
programmable electronic safety-related systems and IEC 61511,
Part 1, Functional safety—Safety instrumented systems for the process industry sector were used for relevant calculations.
Findings
The study concluded the following:
• An all-electric autonomous subsea HIPPS is capable of meeting
SIL 3 requirements and safely replacing a hydraulic HIPPS.
• Such a HIPPS will require varying levels of development to reach
a TRL suitable for deployment. The authors expect that a 5 to 7-in.
HIPPS in the 5,000 to 10,000 psi pressure class could be developed, tested, and ready to deploy in an offshore subsea test or
a non-critical application in as little as two years. A larger 9-in.,
15,000-psi system would take longer, perhaps fve years.
• Hydraulic technology has a clear lead at this point, having been
deployed for over a decade in subsea HIPPS as well as far longer
in tree and manifold applications.
• Many of the components on a HIPPS are already electric – sensors and logic solvers for example. Little if any qualifcation will
be necessary for these. The primary effort for these components
will be integration into an all-electric HIPPS.
• The electric actuators and associated components, particularly
ones suitable for large-diameter, fail-safe fnal element valves, are
the critical components requiring further qualifcation.
•Electric fail safe (spring return) actuators make use of generally
accepted methods to maintain the valves in the open position with
minimum power input, generally less than that required for a 100
