Tài liệu PIPELINE PIGGING TECHNOLOGY- P5 doc

Interactive editing The functions available in this category are used to input or amend any item of information held on the database.. Bulk loading Functions are available to bulk load n

items, e.g observations The user moves between screens using the function

keys

(Hi) To incorporate as much flexibility as possible into the design

Several categories of data are implemented in library form, to avoid data

duplication, provide searching facilities and to allow for the possibility of

extending data types Example: anode type library, inspection equipment

library

A system-parameter library holds details such as terminal and output

device characteristics, to accommodate future requirements, and parameter

values used by a number of functions (scaling details, etc.)

A parameter-driven library was designed in order to hold observations

made during surveys (e.g SU: suspensions) and their parameters (e.g length,

height) In this way, new observations and parameters can easily be added by

the users

(iv) To provide adequate security restrictions for the system

It is important to protect the data from unauthorized use Access to the

system is based on each user having a unique user identification and

pass-word Access to a specific category of functions is restricted by the user's

security classification On logging onto the system, the user is presented with

a menu of the available categories based on his classification To provide a

secure system it is important that users remember to log off at the end of each

session and also not to leave a logged-on terminal unattended To minimize

the possibility of a breach in security, a timeout facility is incorporated into

the system, so that any terminal which has had no activity for a given period

of time is automatically logged off

System functions

There are five categories of functions available on the system Each user

has access to one or more of these depending on their security classification

Interactive editing

The functions available in this category are used to input or amend any item

of information held on the database The data entered is validated against the

information already held to ensure it is consistent Users are also able to delete

a particular occurrence of a record type but the option to delete a complete

hierarchy of records (e.g in inspection) is limited to the database

mainte-nance category

Bulk loading

Functions are available to bulk load nearly all of the inspection results

automatically, from magnetic tape, thus reducing manual input to a minimum

The tapes are completed offshore during the surveys, or shortly after, by the

inspection contractors The format of the tapes has been designed to

accom-modate the requirements of this system and the standard working procedures

of contractors

The following data can be "bulk" loaded: acoustic inspection,

incorporat-ing pipe burial condition, trench condition and observations; ROV

inspec-tion, incorporating observations, longitudinal profile, transverse profiles, and

CP potential

Reporting

A number of reports are available either for display at the terminal or

output to the printer On choosing the report required, the user is prompted

to enter the selection criteria and the output device Selection criteria can be

such as: a range of PKs, particular type of observation, dates, etc

There are printed reports available for any data held on the database, such

as list of inspections, list of observations (Fig.2)

In addition, some graphical reports are available which correspond to the

visual charts used in pipeline inspection such as: ROV alignment sheet (Fig 3),

acoustic summary sheet, free span drawing

Analysis

A number of analyses can be requested which allow the results of several

inspections to be processed

The results from all inspections performed to date can be merged in

summary charts providing the latest information available at any point of the

pipeline Summary charts available include:

pipe burial condition (Fig.4);

summary of observations (Fig.5);

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Fig.2 Typical list of observations.

Fig.3.Typlcal ROY alignment sheet

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Fig.4 Pipe burial condition chart

Fig.5 Observation summary chart.

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Fig.6 Summary chart comparison.

Fig.7 Suspension history.

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summary of CP potential;

summary of pipe-wall anomalies (revealed by internal inspection)

In addition, results from different campaigns or from different inspection

types can be presented on a comparison chart Comparison charts available

include:

comparison between summary charts (Fig 6);

comparison between ROV and/or acoustic alignment sheet;

suspension history (Fig.7)

Those programs can require a longer processing period; therefore to avoid

locking the users terminals they can be run as background tasks, the results

being sent to either the printer or a plotter, or kept in a file In this way the

user is able to continue using the terminal for other functions while the

analysis is being carried out

Database maintenance

This category of function has the highest security classification on the

system as it contains the functions used to maintain the integrity and flexibility

of the database It is the only category which allows users to delete a complete

hierarchy of data items, e.g a pipeline or a complete inspection

Users in this category are responsible for maintaining the libraries and for

allocating system parameters and security classifications

System software selection

Prime being the selected computer hardware it was therefore desirable to

select Prime Systems' software if this could meet the needs of CIS-PIPELINE

This would minimize any third-party involvement in order to ensure future

compatibility of hardware and software

DBMS, Prime's Codasyl database management system, was selected as it

would easily map the network and hierarchical structures of the pipeline

inspection data It was also capable of giving fast access to the large amount

of data involved In addition it has a query and report generator (DISCOTER)

which could be used for ad hoc enquiries.

In general the Prime PT2OO terminals are used for standard editing and

reporting However the system also includes a number of graphical reports

and analyses which are displayed online using the Tektronix 4107 terminal

The FORMS screen handler is used to give a consistent and effective interface

to the user A third-party GKS graphics package was also selected (the

graphical kernal system meets ISO and ANSI standards)

A Pragma 4160 high-resolution dot-matrix printer was selected to produce

hard copy output of the graphical reports and analyses It is capable of

producing large continuous plots and is a very economical alternative to large

pen plotters The system was developed using FORTRAN 77 as the

program-ming language and the Prime is run under its native operating system,

PRIMOS

HOW THE SYSTEM MATCHES UP TO

EXPECTATIONS

CIS-PIPELINE was commissioned during August, 1986 The following few

months were devoted to loading the initial database Some of the data was

entered manually, including:

construction and environmental data;

major results from inspection and maintenance earlier than 1983: burial

condition, free spans, area inspected

All the results since 1983 were available on floppy discs, provided by the

contractors After reformatting, these were loaded onto the system

The system was successfully used for the 1987 inspection campaign and

most of the initial expectations were met as follows:

Improvement of the awareness of the pipeline condition

Performing analyses was much easier than before, therefore these were

conducted more frequently and were more accurate As a result, the

engi-neers gained a better knowledge of the pipelines and had more confidence

in the results

Examples of studies carried out:

trend analysis of burial condition and free spans;

during the summer of 1987, a major review of the Frigg pipelines'

condition over the past ten years was performed The result of this

study is now-frequently used as a reference

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Shortening of response time in finding information

The improvement in this area was very significant In addition, there was

more confidence that information can be retrieved quickly when required

Examples where this has been beneficial are:

ad hoc presentations to management and authorities;

preparing of annual reports;

answering of questionnaires from authorities such as 'Pipeline

Aban-donment Study Database'

More cost-effective scope of ROV inspection

The system was used during the preparation of the 1987 ROV campaign

It was found that the scope of work was prepared in a shorter time and that

it was necessary to survey fewer areas than in previous campaigns This led

to a reduction of cost However this may not be entirely attributable to using

the system

Reduction in the number of reports

It was decided to keep the old reporting system in 1987, in parallel with

CIS-PIPELINE In the light of the good performance of the system, it should be

possible to reduce the number of reports supplied by the contractors in 1988

ADDITIONAL BENEFITS

On top of the foreseeable advantages, a number of additional benefits have

arisen from using CIS-PIPELINE over the past 18 months:

(a) Better reporting standards - Due to the establishment of a detailed

format for the magnetic tapes, inspection contractors have been

forced to report in a more standardized way Consequently, the

quality of reporting has improved It is also easier to cross reference

results from different inspections

(b) Discovery of a number of inaccuracies in earlier data - The initial

database loading was accompanied by a complete re- validation of

the data Some inaccuracies were detected in the as-laid data (anodes

position) and in earlier inspection reports (calibration of CP

poten-tial) These could have led to problems, had they remained

undetec-ted

(c) Lower cost of the ROV inspection in 1987 - The scope of the ROV

inspection was reduced in 1987 Although this may not be due

entirely to using CIS-PIPELINE, a number of areas where the lines

were buried were easily identified and eliminated from the scope of

work

(d) Preventive maintenance - In the past, only free spans exceeding the

maximum allowable length were stabilized In 1987 free spans

nearing the limit were added to the scope if they were in close

proximity to other free spans requiring maintenance Using the

system was of great help in identifying these areas

(e) Wider knowledge of the pipeline - Previously, due to the large

amount of data, a limited number of people had a detailed

under-standing of the pipeline condition Now, however, this knowledge

is far more widespread due to the ease with which users may access

the data and perform analyses

CONCLUSION

Having been in use for the past 18 months CIS-PIPELINE has matched the

initial expectations and provided a number of additional benefits

In particular the successful use of the analysis functions, such as those

providing the ability to retrieve the most recent information about each

section of the pipeline, or compare results from different inspections, has

greatly improved the awareness of the pipeline condition Other major

benefits include:

improved scope of ROV inspection;

more efficient use of the engineer's time;

greater confidence in the ability to retrieve any information when

required;

improved reporting standards

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The decisions taken on the technical options during the initial stages have

been confirmed through the usefulness and resilience of the system The

design has proved robust and well suited to the requirements For instance a

number of additions have been easily made to the libraries by the users,

enabling the system to accommodate changing requirements

10 YEARS OF INTELLIGENT PIGGING:

AN OPERATOR'S VIEW

INTRODUCTION

Total Oil Marine pic has operated, for the last decade, a gas-transportation

system between the giant Frtgg field in the Northern North Sea and the

St.Fergus Gas Terminal on the NE coast of Scotland The reserves of the field,

which straddle the Norwegian/UK boundary, have been exploited by the

construction of two large-diameter high-pressure gas pipelines to St.Fergus

This paper looks at the background to the pipelines, and in particular at the

decision to use internal inspection by various types of intelligent pigs as an

element of internal condition monitoring devised for a gas-transportation

system

PIPELINE DETAILS (SEE FlG.l)

The two lines from the Frigg field to St.Fergus were constructed during

1974-1976 One line is owned by the UK Association (see Acknowledgements

for definition of this group), and the other by the Norwegian Association (see

Acknowledgements) Both are opera ted by Total Oil Marine pic Details of the

lines are as follows:

diameter 32in OD

wall thickness 0.75in

length (each) approx 360km

steel API 5LX 65

maximum allowable operating pressure 149 bar

The pipelines run parallel to each other approximately 100m apart in

water depths of up to 155m Approximately halfway to St.Fergus there is the

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Fig.l Total Oil Marine pic's North Sea pipelines.

manifold compression platform MCP01 In 1982 the capacity of the pipelines

was further increased with the installation of compression facilities on

MCP01 In addition, the platform acts as a pig launching/receiving station and

allows other gas to join the system, which includes gas from the Tartan,

Ivanhoe and Rob Roy fields.

At Frigg a number of other fields are linked to the gas-transportation

system, namely Odin, East Frtgg, NE Frigg and Alwyn North The line to

Alwyn North is 24in OD, and is operated by Total Oil Marine pic (ownership

is the same as for the UK Association) In addition, Total Oil Marine pic

operates a 12-in oil pipeline from Alwyn North to Ntnian Central, as well as

subsea flowlines around Alwyn North.

GAS QUALITY AND QUANTITY

Frigg field gas has historically made up over 90% of the gas transported to

StFergus, and is a sweet product The levels of H2S and CO2 are extremely low,

and therefore the lines were fabricated for sweet service In addition, the lines

have no corrosion allowance except due to using standard API wall thickness,

and any additional amount from the manufacturing process

This is one of the reasons why a great deal of effort has been placed on

internal condition monitoring

A second reason for employing a detailed monitoring programme is the

importance of the lines to the UK in general The pipelines have recently

completed the delivery of 200 Billion Sm3 (7.02 trillion Sft3) of gas to British

Gas The maximum flow on any one day was 80.4 MSm3 (2.82 Billion Sft3)

More importantly, the system has, on average, annually delivered between

30-40% of all of UK gas supplies since operations commenced in 1978

Occasion-ally, monthly deliveries have been up to 55% of the UK gas requirements

Internal condition monitoring of the Frigg System is based on the following

methods:

product control analysis of the gas transported;

corrosion monitoring by means of corrosion probes and coupons; and

internal inspection

The first two operations are carried out on most lines, but we believe they

are limited in application Product control is not fool-proof; operational errors

do occur, and in particular the most important measurement (the water

dewpoint) is very problematical

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