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Design of Measurement Systems capable of supporting Asset

Integrity Management: a Subsea Production Systems Case Study

The second assignment of the Measurement Systems module is a design

exercise that will allow you to identify the parameters that have to be

measured by specific instrumentation in order to enhance production and to

increase availability of a subsea field. A typical sub-system of a subsea

production system should be considered as a case study for this coursework

(analysis can focus on manifolds, XTs, subsea compression systems, multiphase

pumps etc). The boundaries of the systems/sub-systems you should be

focusing on are depicted in Figure 1-1 (Recommended Practice DNVGL-RP-002:

Integrity Management of Subsea Production Systems).

In order to account for production losses, the OEM designers of subsea

equipment have to identify the threats/critical components affecting a

system/sub-system throughout the design phase of that particular asset. A

bow-tie diagram showing barriers to eliminate and prevent causes of

hazardous events and the ones to control consequences and effects is depicted

in Figure 1-2 of the previously mentioned document. According to the authors

of DNVGL-RP-002, a threat is an indication of an impending danger or harm to

the system, which may have an adverse influence on the integrity of an asset.

Each threat may lead to a failure, undesirable situation or an abnormal

condition. The possible consequences of such an occurrence can be described

in terms of failure modes.

Some failure modes may be due to a specific degradation mechanism, while

others are event based. Several techniques can be employed to account for the

effects of failure modes affecting a given system like Hazard and Operability

study (HAZOP), Reliability Block Diagram (RBD), Fault Tree Analysis (FTA), and

Failure Mode Effects and Criticality Analysis (FMECA). The design exercise you

are required to carry out as part of this coursework will consist of a Failure

Mode Effects and Criticality Analysis (FMECA) report that has to be constructed

for the system you have selected. According to the many practitioners, in a

Failure Modes Effects and Criticality Analysis (FMECA), each individual

component of the system is assessed for its possible failure modes, and for

each failure mode it is determined what the effects of the failures are and how

critical these effects are. Criticality is defined as the combination of the

probability of the failure mode and the severity of its effect. The objective is to

rank the criticality of components that could result in injury, damage or system

degradation through single-point failures in order to identify those

components that might need special attention and control and monitoring

measures during design or operation. The FMECA report will form the

foundation of the measurement systems design exercise as it will guide the

instrumentation analyst in the selection of the suite of tests and

measurements capable of supporting the operational integrity function. Your

report should clearly highlight the informed decisions in selecting a specific

type of instrumentation.

Guidance

Step 1

Subsea assets currently used in the Oil & Gas industry sector can be considered

as complex systems in that they require different types of equipment with

various causal relationships among components and process and processes

(Laibin & Jinqiu, 2013). Failures that occur in service can cause significant

downtime of the production, can compromise the quality of the product and

also have a significant impact on the environment. Therefore, should and must

be detected as soon as possible and the causes, mechanism, faults, symptoms

and failures should be very well understood and communicated to everyone

involved in designing, installing, commissioning, operating, maintaining and decommissioning

these types of equipment.

A list of references that might guide you throughout a literature review on how

specific sub-systems of a subsea production system operate, on the typical

faults affecting these pieces of equipment in service and the instrumentation

currently employed to support the operational integrity function is provided

(References list.pdf). Please note, the reference list is not exhaustive. A very

complete reference is the Subsea Engineering Handbook, Source: Glasgow

Caledonian University Library, Catalogue Publisher: Gulf Professional Pub Date:

2012, ISBN: 012397805X, 0123978041, 9780123978042, 9780123978059

(available also as an e-book).

The literature will include a critical analysis of relevant and current sources

appropriate to academic writing, such as academic journals and proceedings

from conferences and industrial documentation and workshops. Apart from

design specifications and typical failures affecting various components within

these systems, you are also required to specify/identify the type of

instrumentation that are currently employed to monitor the occurrence of

faults in Oil & Gas Subsea applications, to diagnose (to detect and isolate)

these faults and to make predictions regarding remaining useful life (RUL) and

end-of-life (EOL) (if such functions are available).

Before attempting the assignment, you should ensure that you clearly

understand what is required in a literature review. A literature review is not a

collection of passages from various sources. It should be your own critical

discussion of the subject based on what you learn from the literature. This task

should be your first step before attempting any analysis of any particular

equipment.

Step 2

Once information about failure modes affecting different components has

been identified, you are required in the first instance to fulfil the role of a

reliability engineer and to identify the critical components of a system. A

FMECA report should be constructed for the system/sub-system under

investigation. Any template for the FMECA report will be accepted for this

report (An industry widely accepted format for this type of analysis is the MILSTD-

1629. A snapshoot of such a report is depicted in FMECA Template.pdf

file).

The actual design of the measurement system capable of supporting the

integrity management function requires you to use the FMECA report

(previously created) of subsea equipment and to identify potential functional

issues and mitigate risk by adding instrumentation throughout the design

process. The Recommended Practice Subsea Production System Reliability,

Technical Risk and Integrity Management, API RECOMMENDED PRACTICE 17N,

SECOND EDITION 2015

(http://ballots.api.org/ecs/sc17/ballots/docs/APIRP17NBallotDraft.pdf) states

that it is recommended that operators, working with equipment suppliers,

undertake a detailed analysis of the equipment and/or system failure modes

and mechanisms to determine the best available means to:

— Confirm the status of equipment and/or system (detect failure and time of

failure),

— Identify and track deterioration in function or performance of equipment

and/or system prior to failure,

— Identify when deterioration may require corrective action.

A failure modes and effects criticality analysis (FMECA) or Reliability Centered

Maintenance (RCM) analysis may be used to support identification of the most

appropriate method for detecting failure and deterioration of functions. For

instance a FMECA may be used by asking specific questions such as:

— Component function and functional failure mode: can this be directly or

indirectly monitored?

— Failure mechanisms and causes: can these be monitored or measured?

— Failure effects and consequences (Local or Global): can these be detected or

measured?

The requirement for an effective method for failure detection or condition

monitoring will depend on a number of factors including;

— The risk of the failure (i.e. the consequence and frequency of occurrence),

— Whether the failure is evident to the operator or not (revealed or unrevealed

failure),

— Whether additional compensating provisions are available or not,

For example, if the failure mode under consideration is an unrevealed failure

and the consequences of the failure have significant health, safety,

environmental or financial implications, then this should drive the requirement

for an effective periodic testing regime. Ideally this testing would be conducted

in such a way as to support condition monitoring of the item.

The outcome of the FMECA or RCM analysis will be the selection of the most

appropriate means of data collection e.g. through:

— Inspection (to detect damage or deterioration),

— Equipment testing (to confirm functional capability of active or standby

equipment (e.g. valves),

— Condition monitoring (instrumented monitoring system and signature

monitoring),

— Process monitoring (temperature, pressure, flow).

These data may be used to inform decisions between maintenance and

integrity management actions such as:

— Condition based maintenance: repair or replace when condition reaches a

defined limit,

— Scheduled maintenance: undertake maintenance action at specified times,

(e.g. marine growth cleaning, bolt tightening, etc.),

— Scheduled replacements: replace equipment when a specific age is reached,

— Run to Failure: repair or replace equipment when failed.

Objective

The objective of this exercise is to identify the failure modes affecting a subsystem

of a subsea production system, to carry out a FMECA and to specify the

instrumentation capable of detecting these faults. A good starting point is to

focus the research on critical components of subsea equipment and to identify

how such equipment is currently monitored by this industry sector. Offshore

REliability DAtabook (OREDA) is the reference database on this subject

gathering information from several large operators in the Oil & Gas arena.

Please note that the OREDA is only collating data on failure modes affecting

various components used in subsea equipment. Instrumentation has to be

deployed on subsea equipment for improvement of reliability, availability,

maintenance and safety in exploration and production. Your task is to select a

bit of equipment within a typical subsea field, to identify faults affecting this

equipment in service, and to identify the fault signatures (based on a failure

mode effect and criticality analysis) that can support the specification of

instrumentation capable of detecting and isolating the faults considered for

the analysis.

Quotation, citation and referencing

Quotation, citation and referencing serve distinct but complementary

purposes.

Quotations tell the reader when you have used someone else’s words.

Citations acknowledge the work of others and tell readers which references

are the sources for the specific information that you are presenting.

References help readers to track down the original source so that they can

check for themselves.

Quotation

Any reader of your literature review (including someone not familiar with the

subject or source material) should be in no doubt whatsoever which words and

ideas are your own, and which are the work of another person. It should not

usually be necessary to copy large passages from your sources. Note that no

marks are awarded for the ability to cut and paste. Where you find it necessary

or useful to copy a phrase, that phrase must be clearly shown with quotation

marks ( “) placed around the quote. Note that no marks are awarded for

demonstration of an ability to change or replace words in a quotation

unnecessarily. Where it is necessary to alter a quote, perhaps to change tense

or omit words to better fit the context in which you are embedding it, then

that alteration should be shown with square brackets [ ] around the changed

words and with an ellipsis … to signify any missing words.

Referencing

In writing your literature review, you will make use of a variety of sources of

information; primarily academic journals and conference papers. At the end of

your literature review, you must include a “References” section. This section

will list the sources that you have used; those which have been cited within the

body of your report (see below).

The references may be numbered or unnumbered. If unnumbered, they should

be arranged in alphabetical order of the last name of the first author. Each

reference should include the author(s), date of publication, title and full

bibliographic information (e.g. journal volume and issue, ISBN/ISSN, book

publisher, etc.). If your references are numbered, it is generally good practice

to sort them into the order that they are first cited in the text; but this is not

essential. Internet URLs (uniform resource locators) are not sufficient on their

own because web pages are neither static nor permanent. The idea is to allow

the reader to be able to easily track down the source even if it moves; and

preferably with sufficient redundant information that it can be traced even if

you make a mistake in part of the reference.

Citation

Whenever you place a quotation in your review, you must also include a

citation that lets the reader identify its source. Citations tell the reader which

of the references listed at the end is the source of the information. You must

also include a citation where ever you use ideas, concepts, data or figures from

elsewhere, even if you put the ideas into your own words. Citations are not

only for direct copying.

The most common citation styles are Harvard, where you indicate the author

(and optionally date) of a source; and numeric, where a number is used. The

citation tells the reader which of the references (listed at the back) is the

source of the information. It provides a mapping between the body of your

text and the references section. You must ensure that it requires no effort on

the part of the reader to identify which reference a citation refers to.

As well as acknowledging the work of others, citations perform a role in telling

the reader which sources provide evidence for your statements. If multiple

sources say similar things, then it is good practice to give multiple citations.

This provides a firmer foundation for your work, particularly if one of the

sources is subsequently found to be unreliable.

Word count

There is no minimum word or page count. The ability to write clearly and

concisely is a useful skill to acquire. Concentrate of the quality rather than the

quantity of what you say. Make sure you have to clear sections in your report:

the literature review and the documentation that describes the content of the

model and the output of your analysis. Please make sure you comment the

content the propagation table.

Assessment

The marking scheme for this assignment shall be as follows:

Selection of literature / 20

Understanding of the system/components’ function,

failure modes and effects of failure modes throughout the system / 10

FMECA report and specification of the instrumentation / 10

Critical appraisal / 10

————————————————————————————

Total /50 marks

Note:

The Subsea Compression System (SCS).pdf contains a schematic of a subsea

compression station and a brief description of its functions. This system can be

used as a starting point for this coursework.

Brief description of a subsea compression station

? Well stream is a multiphase flow; mixture of (oil+ gas+ water) with possibility of solid debris.

? The globe valve is electro-hydraulic operated; suitable for shorter step-out (distance between compression station

to top-side facility) approximately 50km.

? Inlet-cooler is to cool the well stream to match operating requirement.

? The separator is vertically oriented; it separates the multiphase flow into multi-level phases (oil, and water) by the

use of a weir plate, while the gas phase escapes naturally and transported to the wet gas compressor (WGC). Water

and sand is transported to non-producing reservoir by the water injection pump, while the oil phase is transported

to the multiphase pump (MPP). The MPP is a helicon-axial pump, driven by electric motor in a rotor-dynamic

fashion. The impeller arrangements add kinetic energy to the oil flow rate, while the gas is at the bottom because of

its density, this creates region of low and high pressure. The flow rate is discharged through the volute. While on

the WGS, the low energy gas flow rate hurls around the impeller of the compressor which adds kinetic energy to it,

this kinetic energy is slowed down to potential energy in a form of pressure rise by the static diffusers, and

discharged through the volute.

? In an even of cavitation on the MPP as a result of gas pockets on the vane cavities of the impeller, the minimum

flow vale opens and the flow rate is routed back to the separator to increase mixture density pressure and increase

intake of flow rate.

? In an event of surge on the WGS, the anti-surge valve opens, the volumetric flow rate is routed through the antisurge

cooler were the it gets cool down as a result of high temperature and violent pressure rise, and transported

back to the separator. This will increase the intake of volumetric flow rate and move the compressor away from

surge line, and the flow rate is now discharged through the volute.

? When all conditions meet the operational requirement, both oil and gas phase will be mixed together and

transported to topside facility for further separation.

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