STRØMMEN_1995_ FSM - non-intrusive monitoring.pdf

8/16/2019 STRØMMEN_1995_ FSM - non-intrusive monitoring.pdf

1/6

Anti-Corrosion Methods and MaterialsFSM — non-intrusive monitoring of internal corrosion, erosion and cracking

Roe D. Strømmen Harald Horn Gaute Moldestad John Kristian Ramsvik Kjell R. Wold

Ar ticle information:To cite this document:Roe D. Strømmen Harald Horn Gaute Moldestad John Kristian Ramsvik Kjell R. Wold, (1995),"FSM — non-intrusivemonitoring of internal corrosion, erosion and cracking", Anti-Corrosion Methods and Materials, Vol. 42 Iss 6 pp. 3 - 6Permanent link to this document:http://dx.doi.org/10.1108/eb007373

Downloaded on: 20 May 2016, At: 09:29 (PT)

References: this document contains references to 0 other documents.

To copy this document: [email protected]

The fulltext of this document has been downloaded 135 times since 2006*

Access to this document was granted through an Emerald subscription provided by emerald-srm:478531 []

For Authors

If you would like to write for this, or any other Emerald publication, then please use our Emerald for Authors serviceinformation about how to choose which publication to write for and submission guidelines are available for all. Please visitwww.emeraldinsight.com/authors for more information.

About Emerald www.emeraldinsight.com

Emerald is a global publisher linking research and practice to the benefit of society. The company manages a portfolio of more than 290 journals and over 2,350 books and book series volumes, as well as providing an extensive range of onlineproducts and additional customer resources and services.

Emerald is both COUNTER 4 and TRANSFER compliant. The organization is a partner of the Committee on PublicationEthics (COPE) and also works with Portico and the LOCKSS initiative for digital archive preservation.

*Related content and download information correct at time of download.

http://dx.doi.org/10.1108/eb007373


2/6

C O N T R I B U T E D P P E R S

FSM - non-intrusive monitoring

of internal corrosion erosion and

cracking

Roe D.

Str mmen

Harald Horn Gaute

Moldestad

John Kristian Ram svik and

Kjell R. Wold

Corrosion m onitoring and inspection is

commonly done in industry, for a wide

range of applications:

inspection of wall thickness and

cracking of pipework for safety

and maintenance planning;

monitoring for control of

corrosion mitigation programmes,

e.g. injection of corrosion

inhibitors;

research, e.g. inhibitor testing and

materials evaluation.

Mostly, corrosion monitoring has been

carried out utilizing various intrusive

moni tor ing techniques. Such tech

niques provide high sensit ivity and

accord ingly ear ly in format ion ;

however, the validity of the

information may often be questioned,

since the methods use foreign samples

installed into the pipe as the m onitored

objec t . The methods a lso have

theoretical l imitations and practical

disadvantages such as requirements for

space for retrieval operations, possible

complica t ions dur ing re t r ieval and

possible leaks along the probe.

Inspection is normally based on

various NDT techniques and by the use

of intell igent pigs for assessment of

pipeline corrosion along its entire

length. Such inspection is costly, and

the sensitivity is low compared with

the corrosion monitoring techniques.

Hence, inspection has a limited value

for corrosion control and mitigation.

FSM - the field signature method -

is a non-intrusive method for

monitoring internal corrosion, erosion

and cracking. This means that the

sensing electrodes and all other

equipment are placed on the outside of

the pipes, tanks or vessels to be

moni tored . In compar ison wi th

t rad i t ional cor rosion moni tor ing

methods (probes ) , the opera t ional

advantages of the FSM are:

There are no components being

exposed to the corrosive, abrasive,

high temperature and high pres

sure environment often found in

process piping, or the corrosive

and often hostile environment of a

subsea or buried pipeline.

There is no danger of introducing

foreign objects into the piping.

There are no consumables . The

monitoring system can be

designed for a service l ife

comparable with the piping, tank

or vessel

itself.

There is no danger of leaks in

access fittings or of unsuccessful

retrieval operations.

Measurements are done on the

wall of the pipe, tank or vessel

itself,

not on a small probe or test

piece.

The sensitivity and reliability are

better than those of NDT

techniques.

The FSM method was developed and

patented by the Center for Industrial

Research (SI) in 1985/1986[1]. Corr-

Ocean has acquired all rights from the

SI for worldwide commercial exploita

tion of the FSM technique. The first

f ield installation of the FSM was

comm issioned in 1991, and the FSM

has since been installed in a wide range

of applications, mostly in the oil and

gas industry, but also for R&D

purposes and in the nuclear power

industry. The first FSM subsea systems

were installed on a 12-inch pipeline for

Elf Petroleum Norway and a ten-inch

flowline for Shell Exploration and

Production UK in 1994[2].

Principle

The FSM is based on feeding direct

current through the selected section of

the structure to be monitored, and

sensing the pattern of the electr ical

f ield by measuring small potential

differences set up on the surface of the

monitored object. By proper interpreta

tion of these potential differences, or

rather changes in potential differences,

conclusions can be drawn, e.g. pertain

ing to general wall thickness reduction.

Local phenomena can be monitored

and located by performing a suitable

number of potential measurements on a

given area.

The FSM is unique in that all

measured electr ic potentials are

compared with initial values measured

when monitoring of the object started.

These values represent the init ial

geometry of the object, and may be

regarded as the object 's f ingerprint.

Hence the name of the method. Plate 1

shows an FSM-inst rumented p ipe

section with transformer for feeding

electric current to the pipe section and

sensing electrodes distributed over the

pipe surface.

The monitored area is located

between tw o electrodes for feeding the

exci ta t ion cur ren t . Any poten t ia l

measurements between two selected

electrodes in the matrix are compared

with a measurement be tween two

reference electrodes and to the

A n t i - C o r r o s i o n M e t h o d s

a n d M a t e r i a ls ,

V o l .

4 2 N o . 6 ,

1 9 9 5 ,

p p . 3 -6 , © M C B

U n i v e r s i ty

P r e s s ,

0 0 0 3 -5 5 9 9 A C M M V o l .

4 2 N o . 6 , 1 9 95


3/6

cor responding in i t ia l va lues when

monitoring started, i.e. the fingerprint.

The so-called fingerprint coefficient

(

FC

) is calculated according to the

expression as follows for each set of

measurements:

FC

Ai

= (B

s

/A

s

*

A

i

/B

i

- 1) * 1000

(ppt).

FC

Ai

= fingerprint coefficient for

electrode pair

A

at time

i

.

s

=

voltage for electrode pair

A

at start-up.

B

s

= voltage for reference pair

at start-up.

Aj -

voltage for electrode pair

A

at time

i

.

B

i

= voltage for reference pair

at time

i

.

The

FC

is the parameter which is used

for analysing corrosion rates and

accumula ted cor rosion . The

FC

is

expressed in parts per thousand (ppt)

and corresponds to reduction in wall

thickness in ppt when monitoring

general corrosion or erosion. When

monitoring star ts, the

FC

values are

always zero.

The reference pair of electrodes is

located in the vicinity of the

monitoring electrode matrix, but in an

area where corrosion will not occur.

This is necessary in order to achieve

ef fec t ive compensat ion for ( smal l )

f luctuations in temperature and

excitation current. Different practical

arrangements have been developed for

securing sufficiently small temperature

gradients between reference and

monitoring electrodes.

A very high sensitivity is achieved

by statistical filtering techniques. This

facilitates high-resolution monitoring

even when measurements are

performed on the opposite side of the

corroding wall as will be the case for

in ternal cor rosion moni tor ing .

Resolution figures obtained in practice

represent less than 0.05 per cent (0.5

ppt) of the wall thickness.

pplications and experience

Topside/land-based applications

The first field installation of the FSM

was on Shel l Expro ' s Dunl in A

platform in August 1991. (We refer to

earlier publications where results from

this first FSM installation at Shell's

Dunlin platform are presented[3,4].)

Since this installation, the FSM has

been installed for a wide range of

appl ica t ions for c l ien ts wor ldwide .

Typical FSM applications have been:

corrosion and erosion monitoring

of topside piping in oil and gas

production;

moni tor ing of land-based p ipe

lines (including buried pipelines);

cooling water pipes in nuclear

power plants;

laboratory use, e.g. at flow loops

for corrosion testing.

The FSM is available with various

configurations and features, and can

therefore be optimized for each

individual application. Plate 2 shows a

"c lamp-on device" , which is very

convenient e.g. for laboratory use and

cooling water pipes in hazardous areas.

The FSM has become particularly

popular for pipeline monitoring,

especially where access to the

monitoring location is difficult (buried

pipelines) . The fact that the FSM

requires virtually no maintenance and

replacement of consumeables (except

replacement of batteries) and that the

service life of the FSM equals that of

the pipeline are important factors in

this respect.

A n t i C o r r o s i o n M e t h o d s a n d M a t e r i a ls


4/6

Experience example

-

pipeline

monitoring

Figures 1 and 2 show data from

existing FSM monitoring stations on

two offshore pipelines in the Gulf of

Mexico. Corrosion inhibitor is injected

into both pipelines at a short distance

upstream from the two FSM stations,

and the corrosion rates are accordingly

expected to be low. This has also

proved to be the case as documented by

the FSM measurements.

FSM data obtained from two

stations fitted to two pipelines onshore

(Figures 3 and 4) indicate even lower

corrosion rates. The difference

between the offshore and onshore rates

seems to be due to low mixing of

inhibitor in the fluids offshore, which

results in inadequate inhibition of the

pipe walls at such short distances from

the injection points. Onshore the

inhibitor is well distributed in the fluid

and a higher inhibition efficiency is

obtained. The similarity of the

monitoring results of the two parallel

pipelines demonstrates an excellent

reliability and successful hits of

adequate location of the FSM

installations.

An additional FSM system has been

installed in a produced water system

where no inhibitor is applied, and the

corrosion rate is accordingly expected

to be high. The accumulated metal loss

plot (Figure 5) confirms significant

corrosion rates for this pipeline.

The experience with the FSM

system onshore and offshore has

proved its reliability in monitoring

pipeline conditions and optimizing the

effectiveness of corrosion inhibition.

The FSM system provides an effective

tool for internal pipeline condition

monitoring and accordingly for

managing a corrosion mitigation

programme.

Subsea installations

The main features of FSM subsea are:

instrumented pipe section of the

pipeline, with FSM electrodes and

current feeding arrangement

permanently fitted to the surface;

retrievable instrument unit (RIU)

that can be installed/retrieved by

divers or ROVs - the RIU contains

all electronic components and a

battery package with an

operational life of five to ten years,

and communication options are

direct via cable or hydroacoustics;

topside data collection and

presentation system.

The first subsea FSM was installed for

Elf Petroleum Norway's Fr y to Frigg

12-inch pipeline at a depth of 119

metres. The system was installed in

summer 1994, and has been functioning

without problems and provides high

quality data. Data communication from

the FSM to the Fr y platform is

provided by hydroacoustics. This first

FSM installation was a test project ,

where Norsk Agip, Saga Petroleum and

the Norwegian Research Council

participated in addition to Elf and

CorrOcean. Plate 3 shows the

Fr

y

FSM section prior to subsea

installation.

A C M M

V o l . 42 N o . 6 ,

1 9 9 5

5


5/6

The second FSM subsea system has

been installed on a 10-inch subsea

flowline for Shell UK's Brent field. The

system has been performing success

fully since November 1994. Shell

considered subsea corrosion monitoring

a requisite for the option of carbon steel

pipeline, and expected FSM to be a

valuable tool for monitoring pipeline

condition, optimizing the effectiveness

of corrosion inhibition and reducing

future inspection costs[2].

Two more FSM subsea systems are

currently on order for A/S Norske

Shell's Troll to Kollsnes 36-inch wet

gas pipeline.

eferences

1.

Hognestad, H., A series of in-house

reports on the FSM, Center for

Industrial Research, Norway.

2 .

CorrOcean News January 1995.

3 .

StrÆmmen, R.D., Horn, H. and

Wold, K.R.,

Corrosion

Paper N o. 7,

National Association of Corrosion

Engineers, 1992.

4 . Str mmen, R.D., Horn, H. and

Wold, K.R., "Monitoring corrosion,

erosion and cracking using FSM -

the electric fingerprint method",

Proceedings

of

th e Sixth Middle East

Corrosion Conference

Bahrain,

1 9 9 4 .

Roe D.

S tr

mmen,

Harald Horn, Gaute

Moldestad, John Kristian Ramsvik and

Kjell R. Wold are all employed by

CorrOcean A . S . , Trondheim, Norway.

A n t i - C o rr o s io n M e t h o d s

a n d

M a t e r i a l s


6/6

This article has been cited by:

1. Fangji Gan, Guiyun Tian, Zhengjun Wan, Junbi Liao, Wenqiang Li. 2016. Investigation of pitting corrosion monitoring using field signature method. Measurement 82, 46-54. [CrossRef ]

2. Fangji Gan, Zhengjun Wan, Yuting Li, Junbi Liao, Wenqiang Li. 2015. Improved formula for localized corrosion using fieldsignature method. Measurement 63, 137-142. [CrossRef ]

3. Giuseppe Sposito, Peter Cawley, Peter B. Nagy. 2010. Potential drop mapping for the monitoring of corrosion or erosion.NDT & E International 43:5, 394-402. [CrossRef ]
http://dx.doi.org/10.1016/j.ndteint.2010.03.005http://dx.doi.org/10.1016/j.measurement.2014.12.008http://dx.doi.org/10.1016/j.measurement.2015.12.040

Documents

STRØMMEN_1995_ FSM - non-intrusive monitoring.pdf