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1 ACCEPTED VERSION Jinzhe Gong, Mak L Stephens, Nicole S Abon, Aaon C Zecchin, Matin F Lambet, and Angus R Simpson On-site non-invasive condition assessment fo cement mota-lined metallic pipelines by time-domain fluid tansient analysis Stuctual ealth Monitoing, 15; 14(5): The Autho(s) 15 Published vesion available via DOI: PERMISSIONS It is impotant to check the policy fo the jounal to which you ae submitting o publishing to establish you ights as Autho. SAGE's standad policies allow the following e-use ights: You may do whateve you wish with the vesion of the aticle you submitted to the jounal (Vesion 1). Once the aticle has been accepted fo publication, you may post the accepted vesion (Vesion ) of the aticle on you own pesonal website, you depatment's website o the epositoy of you institution without any estictions. You may not post the accepted vesion (Vesion ) of the aticle in any epositoy othe than those listed above (i.e. you may not deposit in the epositoy of anothe institution o a subject-matte epositoy) until 1 months afte publication of the aticle in the jounal. When posting o e-using the aticle please povide a link to the appopiate DOI fo the published vesion of the aticle on SAGE Jounals 15 June 16

2 On-site Non-invasive Condition Assessment fo Cement Mota Lined Metallic Pipelines by Time- Domain Fluid Tansient Analysis by Gong, J., Stephens, M., Abon, N., Zecchin, A.C., Lambet, M.F., and Simpson, A.R. Jounal of Stuctual ealth Monitoing Citation: Gong, J., Stephens, M., Abon, N., Zecchin, A.C., Lambet, M.F., and Simpson, A.R. (15). "On-site Non-invasive Condition Assessment fo Cement Mota Lined Metallic Pipelines by Time-Domain Fluid Tansient Analysis." Jounal of Stuctual ealth Monitoing, Septembe, vol. 14, no. 5, doi:1.1177/ Fo futhe infomation about this pape please Angus Simpson at

3 1 3 On-site non-invasive condition assessment fo cement mota lined metallic pipelines by time-domain fluid tansient analysis 4 Jinzhe Gong 1, Mak Stephens, Nicole Abon 1, Aaon Zecchin 1, Matin Lambet 1, Angus Simpson School of Civil, Envionmental and Mining Engineeing, the Univesity of Adelaide, Adelaide, SA 55, Austalia 7 South Austalian Wate Copoation, 5 Victoia Squae, Adelaide, SA 5, Austalia 8 Coesponding autho: 9 1 Jinzhe Gong, School of Civil, Envionmental and Mining Engineeing, the Univesity of Adelaide, Adelaide, SA 55, Austalia 11 Tel: +61 (8) jinzhe.gong@adelaide.edu.au 13 Abstact Pipeline condition assessment is essential to tageted and cost-effective maintenance of aging wate tansmission and distibution systems. This pape poposes a technique fo fast and non-invasive assessment of the wall condition of cement mota lined metallic pipelines using fluid tansient pessue waves (wate hamme waves). A step tansient pessue wave can be geneated by shutting off a sidedischage valve in a pessuised pipeline. The wave popagates along the pipe and eflections occu when it encountes sections of pipe with changes in wall thickness. The wave eflections can be measued by 1

4 pessue tansduces as they ae indicative of the location and seveity of the wall deteioation. A numeical analysis is conducted to obtain the elationship between the degee of change in wall thickness in a cement mota lined pipe and the size of the coesponding pessue wave eflection. As a esult, look-up chats ae geneated fo any specific cement mota lined pipeline to map this elationship. The wall thickness of a deteioated o distinct section can be detemined diectly and quickly fom the chats using the size of the eflected wave, thus facilitating on-site pipeline condition assessment. The validity of this time-domain pipeline condition assessment technique is veified by numeical simulations and a case study using the field data measued in a mild steel cement mota lined (MSCL) wate main in South Austalia. The condition of the pipe as assessed by the poposed technique is geneally consistent with ultasonic measuements. 3 Keywods 31 3 on-site, non-invasive, pipeline condition assessment, fluid tansient pessue wave, wate tansmission and distibution system, wate hamme 33 Intoduction Wate tansmission and distibution pipelines ae citical infastuctue fo moden cities. Due to the shee size of the netwoks and the fact that most pipelines ae buied unde gound, the health monitoing and maintenance of this infastuctue is challenging. Although a numbe of techniques have been developed fo pipeline condition assessment, including visual inspection (e.g. closed-cicuit television inspection 1 ), electomagnetic methods (e.g. magnetic flux leakage method and gound penetating ada 3 ), acoustic methods (e.g. SmatBall 4 ), and ultasonic methods (e.g. guided wave ultasound inspection 5 ), they ae eithe too costly, inefficient fo lage netwoks o invasive 6. Efficient and non-invasive pipeline condition

5 41 4 assessment technologies ae yet to be developed fo tageted and cost-effective pipeline ehabilitation and the pevention of catastophic events such as pipe failue Reseach in the past two decades has shown that fluid tansients 7, 8, which ae also known as wate hamme waves, can be used fo non-invasive detection of defects in pessuised pipeline systems. Fluid tansients ae pessue waves that popagate in the fluid and along a pipeline. A typical tansient pessue wave used fo detecting faults in pipelines is a step pessue wave geneated by abuptly closing a sidedischage valve afte the steady-state flow is established. Theoetically, any physical changes on the pipe wall, such as leaks o wall thinning due to coosion, can intoduce wave eflections. The eflected waves popagate towads the souce of the initial tansients (i.e. the side-dischage valve) and can be measued by pessue tansduces installed on existing accessible points such as ai valves o fie hydants. The aival time of the wave eflection can be used to detemine the location of the defect, and the magnitude of the eflection is indicative of the seveity of the deteioation Typical defects in aging pipelines include leaks, blockages, intenal o extenal coosion and the spalling of cement mota lining in lined pipes. Leak detection using tansient pessue waves has been a focus of eseach fo many yeas and a numbe of techniques have been developed, eithe in the time domain 1-1, in the fequency domain 13-18, o by means of advanced signal pocessing (e.g. wavelet) that involves analysis in both domains Blockage detection has also been studied intensively, eithe fo discete blockages (oifices) 4-8 o extended patial blockages 9, 3. The fequency-domain leak and blockage detection uses the change in the magnitude of esonant esponse o the shift of the esonant fequencies of the pipeline. The pinciple is simila to that used in vibation-based condition monitoing applied to othe aeas 31, In ecent yeas, the use of fluid tansients has been extended to non-invasively assess the condition of the pipe wall. Zecchin et al. 33, 34 studied geneal pipeline paamete identification using fluid tansient waves 3

6 but only limited to numeical analysis. Stephens et al. 35, 36 wee the fist to apply the invese tansient analysis (ITA) to detect degadation of the pipe wall in a mild steel cement mota lined (MSCL) pipeline. The ITA uses an iteative pocess to calibate pipeline paametes fo a numbe of discetised eaches; theefoe, it equies consideable computational effot fo complex systems. achem and Schleiss 37 developed a technique fo detecting a stuctually weak section in a pipeline using a step tansient pessue wave. The wave speed in the weak section was detemined fist and then the stiffness was estimated fom the theoetical wave speed fomula. oweve, challenges ae expected when using thei method to accuately detemine wave speeds when multiple deteioated sections exist in a pipeline. Gong et al. 9 poposed an appoach fo detemining the wall thickness of a single degaded section in an unlined pipeline. It was found that the magnitude of the wave eflection esulting fom a section with a unifom change in wall thickness was diectly elated to the hydaulic impedance of that section. The impedance could then be used to detemine the wall thickness and wave speed in the degaded section. An advanced technique was then poposed by Gong et al. 38 to cate fo the detection of multiple deteioated sections in a pipeline. Only unlined pipelines wee studied and the tansient geneation and measuement wee equied to be conducted at the upsteam face of a closed end. oweve, in eal wate tansmission systems, a geat potion of pipelines used ae cement mota lined metallic pipes, and the equiement of geneating and measuing at a closed end is not always achievable The eseach pesented in this pape develops a technique that enables on-site condition assessment fo cement mota lined pipes by fast time-domain analysis of tansient pessue wave eflections. The location of a defect with espect to the measuement point can be detemined by time-domain eflectomety (TDR) 39 (i.e. using half the measued aival time of the wave eflection multiplied by the wave speed). The pocedue is not discussed in detail in this pape since applications have been epoted in pevious liteatue, such as fo locating leaks 1,, patially closed in-line valves 7 and pipe sections 4

7 with a thinne wall thickness 9. The focus of this eseach is to achieve fast and quantitative detemination of the wall thickness of a degaded section in a cement mota lined pipe using the magnitude of the pessue wave eflection. Mild steel cement mota lined (MSCL) pipe is studied in paticula, but the analysis can be easily extended to any othe types of metallic cement mota lined pipes. Equations ae deived to connect the degee of change in wall thickness of an MSCL pipe to the size of the coesponding wave eflection. Changes in wall thickness fom eithe side of the pipe wall (intenal o extenal) ae consideed. As a esult, plots can be dawn to descibe this elationship fo any MSCL pipeline if the specifications of the intact pat ae known. These plots can be used as look-up chats fo on-site tansient-based pipeline condition assessment in pactice. The validity of this new technique is veified by numeical simulations. The applicability of this technique is veified by conducting wall condition assessment using a tansient pessue tace measued fom a MSCL wate main in South Austalia. Significant wave eflections ae selected using a theshold coesponding to full cement loss and then analysed using the look-up chats. The epesentative wall thicknesses ae detemined fo fou sections that ae believed to have significant loss of the cement mota lining and intenal coosion. The condition of the pipeline detemined using the poposed technique is geneally consistent with pipe wall ultasonic thickness measuements. 13 Analysis of fluid tansients in a cement mota lined metallic pipe This section discusses the elationship between the size of the eflected tansient pessue wave and the degee of change in wall thickness in a cement mota lined metallic pipeline. Fist, the typical measuement setup of the field test layout is outlined. Second, the fundamental equations ae eviewed and then adapted to mild steel cement mota lined (MSCL) pipes. Two scenaios ae consideed: an intenal change and an extenal change in wall thickness. 19 Oveview of Field Expeiments 5

8 A typical configuation used fo field measuement is given in Figue 1. A tansient wave geneato and multiple pessue tansduces ae typically used fo each test. The adopted tansient geneato is a customised side-dischage valve connected to an existing access point (such as an ai valve o scou valve). A small step tansient pessue wave (typically 5 to 1 m in magnitude) is induced by apidly closing (within 1 ms) the side-dischage valve afte opening and eleasing a flow (typically to 4 L/s fo pipes fom 6 to 1 mm in diamete) until steady-state conditions ae eached. The geneated incident wave then popagates along the pipe in both upsteam and downsteam diections. As discussed, eflections occu when the incident wave encountes a physical change in the pipe, such as a section with a eduction in wall thickness. The eflected waves popagate back towads the geneato, and can be measued by pessue tansduces that ae mounted along the pipe (also at existing access points). The wave eflections ae then able to be analysed to detemine the location of defects fom the aival times, and the seveity of the defects fom the magnitude of the eflected wave. By compaing the aival times of a specific eflection as measued by two o moe pessue tansduces at diffeent locations, it can be detemined whethe the eflection comes fom the upsteam o downsteam side of the geneato. Incident step waves Reflected waves Extenal coosion Pessue tansduce Side-dischage tansient geneato and pessue tansduce Spalling and intenal coosion Pessue tansduce 14 6

9 15 16 Figue 1. Typical configuation used in the field fo pipeline condition assessment using tansient pessue waves. 17 Fundamental equations The spalling of cement mota lining (CML) and extended intenal, o extenal, coosion ae common poblems in aging wate pipelines. The deteioation often intoduces a change in wall thickness, which in tun intoduces a change in pipeline impedance. The impedance of a pipeline is defined as 7 B a ga (1) whee B is the impedance of the pipeline, a is the wave speed of pessue waves, g is the gavitational acceleation and A is the intenal coss-sectional aea of the pipe. The wave speed ( a ) can be detemined using the theoetical wave speed fomula 7, 8 a K / 1 ( K / E)( D / e) c () in which K is the bulk modulus of elasticity of fluid, is the density of fluid, E is Young s modulus of the pipe wall mateial, D is the intenal diamete of the pipeline, e is the wall thickness and c is a facto depending on the method of estaint of the pipeline Gong et al. 9 demonstated that the size of the pessue wave eflection fom a deteioated pipe section is elated to any change in the pipeline impedance of that deteioated pipe section. The dimensionless head petubation can be detemined using * B 1 B 1 (3) 7

10 whee * is the dimensionless head petubation of the fist eflected pessue wave and B is the atio of the impedance of the deteioated pipe section to the impedance of an intact section. The dimensionless head petubation, * can also be defined fom the incident and eflected tansient waves as * j1 i i (4) whee j1 is the head of the eflected pessue wave, i is the head of the incident tansient pessue wave and is the steady-state head at the measuement point befoe the geneation of the tansient incident wave (duing which time the side-dischage valve based tansient geneato is open). The values of j1, i and ae measueable by a pessue tansduce. Note that, although appeas in Eq. (4), the dimensionless head petubation size of the eflection ( j1 ( i ). The impedance atio i * is independent fom. In addition, * is only elated to the, note that this can be negative) and the size of the incident wave B is given as B1 B B (5) whee the subscipt and 1 epesent the intact pipe section and the section with a change in impedance (the deteioated pipe section), espectively. 15 Equations adapted to mild steel cement mota lined pipes Fo pipelines with a cement mota lining (CML), the contibution of the lining has to be consideed when calculating the wave speed. Mild steel cement mota lined (MSCL) pipe is used as an example to 8

11 facilitate the analysis in this pape. The coss section of an intact MSCL pipe is shown diagammatically in Figue Figue. Coss section of an intact MSCL pipe ( D is the intenal diamete of the pipe, ec is the thickness of the cement mota lining and e S is the thickness of the steel pipe wall) The cement mota lining has a diffeent modulus of elasticity to that of steel, but its contibution to the wave speed can be included as an equivalent thickness of steel 36. The value of the total equivalent steel wall thickness ( equivalent steel thickness as used in the est of the pape) to be used in the wave speed fomula is the summation of the equivalent thickness of steel contibuted by the CML and the oiginal thickness of the steel. Fo a thin-walled intact MSCL pipe, as shown in Figue, the equivalent steel thickness can be defined as e and witten as E e e e C C S E S (6) whee EC and E ae the modulus of elasticity of cement mota lining and steel, espectively, and e C S and e S ae the thicknesses of the CML and that of the steel, espectively. The same concept of 9

12 equivalent steel thickness was used in Wylie and Steete 8 fo einfoced concete pipes. The use of the equivalent steel thickness [Eq. (6)] fo thin-walled MSCL pipe is justified in the Appendix Assuming the same Poisson s atio fo steel and cement mota, the theoetical wave speed fo an intact MSCL pipe (Figue ) is denoted as a and can be witten as a K / 1 ( K / E )( D / e ) c (7) S whee D is the intenal diamete of the intact MSCL pipe. Similaly, the wave speed in a section with a change in wall thickness can be witten as a 1 K / 1 ( K / E )( D / e ) c (8) S whee a 1, D 1 and e 1 ae the wave speed, the intenal diamete and the equivalent steel thickness, in the section with a change in wall thickness, espectively. As a esult, B can be e-expessed as B a1d a D 1 (9) To facilitate the analysis in subsequent sections, the elative change in equivalent steel thickness, e c, is given as e c e e e 1 (1) 1

13 The aim of this eseach is to develop algoithms fo estimating the emaining wall thickness of a deteioated section fom a measued tansient pessue tace. Fo any pipeline, wall deteioation o a change in wall thickness (which esults in a change in impedance) can occu eithe intenally o extenally o both. Theoetically, thee ae thee possibilities fo the cement mota lining: intact, change in thickness (intenally) and total loss. Thee ae also thee possibilities fo the steel wall: intact, extenal change in thickness and intenal change in thickness. As a esult, thee ae 9 theoetical combinations fo the condition of the pipe wall. Intenal wall deteioation (only) and extenal wall deteioation (only) ae discussed in subsequent sections. Simultaneous intenal and extenal wall deteioation is not discussed in this pape, but it is expected to equie a supeposition of the effects caused by intenal wall deteioation (only) and extenal wall deteioation (only) Fou commonly-seen wall deteioation cases ae identified as illustated in Figue 3: (a) S 1: an intenal change in the thickness of the CML; (b) S : total loss of the CML plus an intenal eduction in the thickness of the steel wall; (c) S 3: intact CML with an intenal change in the thickness of the steel wall; and (d) S 4 : intact CML with an extenal change in the thickness of the steel. Case S 3 exists when the pipeline was initially installed with no lining but lined afte yeas, o a section of oiginal pipe is eplaced by a section in the same nominal size (same outside diamete) but a diffeent class (with thicke o thinne steel wall), o sections of a diffeent class ae installed duing constuction. (a) (b) (c) (d)

14 Figue 3. Longitudinal view of fou sections of MSCL pipe with the changes in wall thickness consideed in this eseach: (a) S 1: an intenal change in the thickness of the CML; (b) S : total loss of the CML plus an intenal eduction in the thickness of the steel wall; (c) S 3: intact CML with an intenal change in the thickness of the steel wall; and (d) S 4 : intact CML with an extenal change in the thickness of the steel wall. 1 An intenal change in wall thickness 3 4 Fo the scenaio of an intenal change in wall thickness, the diamete and wall thickness of the intact and damaged sections can be elated based on the fact that the extenal diamete is constant. If the change is in the thickness of the CML alone [ S 1, Figue 3(a)], the following equation holds D e D e (11) C 1 C1 5 6 whee e C1 is the thickness of the CML in the deteioated/distinct section. In this case, the total equivalent steel thickness is given as E e e e C 1 C1 S E S (1) 7 Substituting Eqs. (6) and (1) to Eq. (11) yields E E D e D e E S 1 1 EC S C (13) 8 Substituting e 1 as given in Eq. (1) into Eq. (13), the atio D1/ e 1 can be witten as 1

15 D1 D ES ec e e (1 e ) E 1 e (14) 1 c C c 9 1 Substituting Eq. (14) into Eq. (8), and then substituting the atio D / e using Eq. (7), the wave speed a 1 can be descibed by a 1 c ( K / ) 1 ec a ( K / ) e a 1 ck / E (15) C 11 Substituting e 1 as given in Eq. (1) into Eq. (14) and eaanging the subsequent equation yields D 1 D1 1 e c e D E S E C (16) 1 13 Substituting Eqs (15) and (16) into Eq. (9), and eplacing D / e with an expession including a as given in Eq. (7), the impedance atio can be descibed by B ( K ) 1 e c K EC ac 1 ec ( K / ) eca 1 c K EC K / a (17) Whee finally, substituting Eq. (17) into Eq. (3), the elationship between the dimensionless head petubation of the fist eflected pessue wave e c fo case S 1 can be obtained as * and the elative change in equivalent steel thickness 13

16 ( K ) 1 e c K EC ac 1 ec ( K / ) eca 1 c K EC K / a ( K ) 1 e c K EC ac 1 ec ( K / ) eca 1 c K EC K / a (18) It can be seen fom Eq. (18) that the dimensionless head petubation * is elated to the elative change in the equivalent steel thickness e c, the wave speed in the intact pipeline a, and physical popeties of the pipeline and fluid that ae typically known (K and ). The value of a can be calculated using the theoetical fomula in Eq. (7), o measued by conducting expeiments. As a esult, when conducting pipeline condition assessment, the value of e c can be detemined fom the value of *, which in tun 3 can be detemined fom a measued tansient pessue tace. A cuve descibing values of * 4 5 coesponding to values of e c can be plotted numeically. An example will be pesented in the numeical simulations section Eq. (18) is fo an intenal change in the thickness of the CML. A negative value of e c epesents a thinning in CML, which can be induced by deteioation. In this eseach, positive e c is also consideed, which epesents a section of pipe with a CML thickness geate than the standad thickness. The lowe bound of e c is eached when the CML is totally lost and is calculated as S e / e 1. 3 Fo case S in Figue 3(b), the elationship between * and e c can be detemined by a simila 31 3 pocedue as used in the deivation of Eqs (11) to (18). The expession of by * fo the S case is given 14

17 * K e c K ES ac E S e S ec K eca cak 1 EC 1 ES es e 1 K / a EC e 1 K e c K ES ac E S e S ec K eca cak 1 EC 1 ES es e 1 K / a EC e Note that the value of ck / ES is in the ode of 1 - so that an appoximation 1 ck / E S 1 used in the deivation of Eq. (19). The possible ange of e c is fom -1 to es is / e 1. The lowe bound coesponds to total loss of the CML plus total eduction of the steel wall, and the uppe bound efes to total loss of the CML, but no eduction in the steel thickness. (19 ) 37 By combining Eqs (18) and (19), a cuve can be plotted fo any specific MSCL pipe to descibe the 38 elationship between * and e c fo cases S 1 and S togethe. A discontinuity is expected in the 39 cuve, which epesents the situation of total loss of the CML, but no loss of the steel wall thickness Case S 3, i.e. intact CML with an intenal change in the thickness of the steel wall, can be analysed by the same stategy as used fo cases S 1 and S. Analysis shows that case S 3 is equivalent to the scenaio of an intenal change in wall thickness in an unlined pipe. Using the appoximation of 43 1 ck / E S 1, the elationship between * and e c in this case is given by ( K / )(1 e ) K E a c c 1 ec K / eca K / a ( K / )(1 e ) K E a c c 1 ec K / eca K / a () 44 An extenal change in wall thickness 15

18 Case S 4 shown in Figue 3(d), i.e. intact CML with an extenal change in the thickness of the steel wall, is discussed in this subsection. An example is a pipe section with a eduction in wall thickness due to extended extenal coosion. 48 The equivalent steel thickness fo case S 4 can be witten as E e e e C 1 C S1 E S (1) The intact pipe and the section with an extenal change in wall thickness have the same intenal diamete D. As a esult, in this case, D can be used in the fomula fo a 1 [Eq. (8)] and B a a B is the atio of the wave speeds, i.e. 1. Using Eqs (7), (8), (1) and (1), the impedance atio can then be deived as B K / 1 ec K / e a () c 53 Substituting Eq. () into Eq. (3) esults / 1 c / / 1 / K e K e a K e K e a c c c (3) In Eq. (3), the lowe bound of e c is es / e, which epesents total loss of the steel wall. A cuve can be dawn fo a specific MSCL pipeline fo Eq. (3), and it can seve as a look-up chat fo pipeline condition assessment. 16

19 57 Numeical simulations 58 Numeical simulations using the Method of Chaacteistics (MOC) 7, 8 wee conducted to veify the validity of Eqs. (18), (19), () and (3). A esevoi-pipeline-valve (RPV) system was studied and a step tansient pessue wave was used as the excitation. The physical details of the pipeline ae those fo the existing MSCL Mogan Tansmission Pipeline (MTP) in South Austalia, which will be futhe discussed in the subsequent case study section. Fo intact sections, the extenal diamete is 76 mm, the intenal diamete ( D ) is 77.5 mm, the thickness of the CML ( e C ) is 1.5 mm and the thickness of the steel ( e S ) is 4.76 mm. Othe paametes used in the numeical study include: the estimated elastic modulus of the cement mota E C = 5 GPa; the elastic modulus of the steel pipe wall E S = 1 GPa; the bulk modulus of wate (at 15 ) K =.14 GPa; the density of wate (at 15 ) = kg/m 3 and the estaint facto fo an axially and lateally estained steel pipe c =.91 (fo a Poisson s atio fo the steel pipe wall of.3). As a esult, the theoetical wave speed and equivalent steel thickness fo an intact section ae calculated as a = 115 m/s and e = 6.5 mm, espectively Plots fo Eqs. (18), (19), () and (3) can be dawn using the physical details of the intact MSCL pipeline. Cuves of Eqs. (18) and (19) ae shown togethe in Figue 4. The point at ec es / e 1 =.38 and * =.76 is the intesection of the cuves of Eqs. (18) and (19) and it coesponds to total CML loss with an intact steel wall. Plots fo Eqs () and (3) ae given in Figue 5 and Figue 6. The lowe bound fo the cuve in Figue 6 is ec es / e =.76. Figues 4 to 6 can be used as look-up chats fo pipeline condition assessment fo the MTP. 17

20 Dimensionless head petubation, * b Intesection e = c * =.76 a a = 115 m/s 76 Relative change in equivalent steel thickness, e c Figue 4. Relationship between the dimensionless head petubation ( ) and the elative change in equivalent steel thickness ( e c ) fo: (a) an intenal change in the thickness of the CML [Eq. (18), S1in Figue 3(a)], and (b) total loss of the CML plus a eduction in the thickness of the steel wall [Eq. (19), S in Figue 3(b)]. Dimensionless head petubation, * a = 115 m/s Relative change in equivalent steel thickness, e c 18

21 Figue 5. Relationship between the dimensionless head petubation ( ) and the elative change in equivalent steel thickness ( e c ) fo the case of intact CML with an intenal change in the thickness of the steel wall [Eq., S3in Figue 3(c)]. Dimensionless head petubation, * a = 115 m/s Relative change in equivalent steel thickness, e c Figue 6. Relationship between the dimensionless head petubation ( ) and the elative change in equivalent steel thickness ( e c ) fo an extenal change in the thickness of the steel wall [Eq. (3), S4 in Figue 3(d)] The fou cases, S 1 to S 4 as shown in Figue 3, ae simulated by MOC in sequence and independently (i.e. in each simulation, only one case was involved). Specifically, the sections of pipe involved in the simulations include: (a) S 1: C1 e = 6 mm; (b) S : S1 e = 3 mm; (c) 3 S : S1 S : e = 6.35 mm; and (d) 4 e S1 = 3 mm. A esevoi-pipeline-valve system was used and the total length of the pipeline was taken as 333 m. The length of each section with a change in wall thickness was appoximately 1 m (with slight 19

22 Dimensionless head petubation adjustment to keep the Couant numbe value to unity) and stated fom 115 m downsteam of the esevoi. The time step used in the MOC was.5 s. A step tansient wave was geneated by closing the downsteam valve within one time step. Fiction was not consideed in the MOC simulations. Pessue esponses wee measued at a point 3 m downsteam fom the deteioated section The theoetical wave speeds in the fou sections ( 1 S to S 4 ) wee calculated using the wave speed fomula with the esults: a 1_ S1= 975 m/s, a 1_ S = 81 m/s, a 1_ S3 = 174 m/s, and a 1_ S 4 theoetical equivalent steel thicknesses fo the fou sections ( S 1 to 4 mm, 1_ S = 95 m/s. The S ) wee calculated as e 1_ S1 = 5.47 e = 3. mm, e 1_ S3 = 7.84 mm, e 1_ S 4 = 4.49 mm. The theoetical elative changes in the 3 33 equivalent steel thicknesses ae calculated as e c _ S1=.14, e c _ S =.5, e c _ S 3=.54, e c _ S 4= The dimensionless head petubations ( ) obtained fom the MOC simulations fo the fou cases ae * given in Figue 7. The values of the dimensionless head petubations ae also shown in Figue S S S S Time (s)

23 37 38 Figue 7. Dimensionless head petubations obtained fom the MOC simulations fo the fou pipe sections with changes in wall thickness ( S 1 to S 4 ) Using Figues 4 to 6, the coesponding values fo the elative change in the equivalent steel thickness can MOC MOC MOC MOC be detemined fo each case, and the esults ae e c _ S1=.13, e c _ S =.519, e c _ S 3=.58, e c _ S 4 =.83. It can be seen that the esults detemined fom the numeical tansient pessue taces ae consistent to a high degee with the analytical esults ( e c _ S1 to e c _ S 4). The small diffeences ae fom ounding eos and the appoximations used in the deivation of Eqs. (18), (19), () and (3). The numeical simulations veify that Eqs (18), (19), () and (3) ae valid, and they can be used fo quantitative pipeline condition assessment. Fo a specific measued wave eflection, potential deteioation scenaios can be listed and the emaining wall thickness fo each scenaio can be detemined. 317 Case study A eal-wold case study is conducted to veify the applicability of the poposed pipeline condition assessment technique. A section of pipe in the Mogan Tansmission Pipeline (MTP) in South Austalia is studied. The section of pipe studied in this pape is fom chainage (location as measued along the pipe length fom some datum) 15 m to C 18 m, coveing scou valve No. 4 (SV4), and ai valves No. 43 (AV43) and No. 44 (AV44). The layout of the section of pipe unde study is given in Figue The MTP is an above gound MSCL wate main between a pump station and a staging tank ove a length of 6.1 km. Duing the field testing, the pump was tuned off and fomed a dead-end bounday. The pipeline system was pessuised by the staging tank. The physical details fo intact pipe sections ( D, 36 e C, S e, e and a ) and othe paametes ( E C, E, K, and c ) have been given in the section S 1

24 numeical simulations. The section between C m and C 1584 m has a known thicke steel thickness of 6.35 mm. oweve, the extenal diamete and the thickness of the CML in this section ae the same as countepats in the oiginal intact sections (Case S 3). A few eplacements with thicke steel wall ae also located in this section of pipe. These eplacement sections ae not consideed hee because of thei shot length (typically a few metes). A tansient geneato, which is a customised side-dischage valve, was used at SV4 to poduce step tansient pessue waves. Flow metes wee connected to the side-dischage valve to measue the steady-state side-dischage befoe the signal geneation. The steady- state side-dischage is used to facilitate the detemination of the magnitude of the incident step wave. Pessue tansduces wee placed at SC4, AV43 and AV44 to measue the pessue esponse. Moe details about the field tests and an analysis of this section of pipe using invese tansient analysis (ITA) ae given in Stephens et al. 36. = 6.35 mm = 4.76 mm AV43 SC4 AV C C 1584 C 173 C 166 C Figue 8. Layout of a section of the Mogan tansmission pipeline The dimensionless head petubations between chainage 15 m and 165 m, as measued at AV43, ae shown in Figue 9 as the solid line. Long-peiod (low fequency) pessue oscillations associated with the opening of the side-dischage valve (to intoduce a side-dischage) have been emoved by a band-pass filte and the oiginal pessue tace and filteed tace ae pesented in Stephens et al. 36. The steady-state head is detemined by aveaging a shot peiod of the data measued befoe the aival of the incident

25 wave, and the esult is = 3.1 m. The magnitude of the incident wave ( i ) is estimated fom the wave font shown in the measued tace (the ange fom the steady state head to the fist peak shown on the top of the wave font, which is 37.8 m), and the esult is 5.79 m The x-axis in Figue 9 is the chainage coesponding to the wave eflections. The chainage infomation is obtained by time-domain eflectomety (TDR) and using the measued aival time of the eflection and the epesentative wave speeds. The aival time of a eflection as measued by a tansduce (elative to the aival time of the wave font) is the time fo a pessue wave to tavel to, and be eflected back fom, the coesponding defect. The epesentative wave speed fo the section between AV43 (C166) and the ight bounday of the thicke-walled section (C1584) is 93 m/s, which is detemined by the known distance and the aival time of the eflection esulting fom the thicke-walled section. The epesentative wave speeds fo the thicke-walled section and the pipe section on its left side ae calculated as 15 m/s and 9 m/s espectively The dashed line in Figue 9 epesents the value of the dimensionless head petubation esulting fom a section of pipe with total CML loss but intact steel wall, which is * =.76. This dashed line acts as a theshold to distinguish significant eflections that esult fom deteioated sections with total CML loss and intenal coosion. The steel wall thickness values wee also measued by an ultasonic thickness measuement instument at 5 m intevals along the MTP between C 149 and C 189. The ultasonic measuements wee taken at eight points aound the cicumfeence of the pipe (P1 to P8, stating fom the top of the pipe and with 45 inteval aound the cicumfeence) at each location. The inteval of measuement was educed to 1 m fo some sections whee changes in steel wall thickness wee detected. The dotted line in Figue 9 gives the aveage steel wall thickness along the section of pipe (aveage of the ultasonic wall thicknesses measuements at eight points aound the cicumfeence). The 3

26 Dimensionless head petubation Steel wall thickness (mm) makes shown in Figue 9 ae ultasonic measuements of the steel wall thickness with values less than 4.3 mm (this value is consideed significant as it coesponds to appoximately a 1% steel wall eduction compaed to the oiginal steel thickness of 4.76 mm as given by the manufactue fo an intact MSCL section) R5.5 R1 R R3 R4 R6 R Chainage (m) Nomalised head Nomalised head fo total CML loss Aveage thickness Steel thickness P1 Steel thickness P Steel thickness P3 Steel thickness P4 Steel thickness P5 Steel thickness P Figue 9. Dimensionless head petubation (as function of distance) measued at AV43 (the solid line), dimensionless head petubation esulting fom a section of pipe with total CML loss but intact steel wall (the dashed line), aveage steel thickness measued by ultasonic sounding (the dotted line), and ultasonic measuements with values less than 4.3 mm (maks as indicated in the legend) Seven significant eflections ae selected fo analysis, shown as R1 to R7 in Figue 9. The selection is based on a compehensive analysis of the tansient taces measued at AV43, SC4 and AV44 in the same test to ensue the selected eflections ae induced by defects that ae located on the left hand side of AV43 (see Figue 8). A eflection coming fom the left hand side of AV43 will appea in the tace measued at 4

27 AV43 fist, then shows at SC4 and finally aives at AV44. The time lag between the aival times of a eflection is consistent with the time fo the initial incident pessue wave taveling fom one point to anothe. By moving the taces measued at SC4 and AV44 fowad in time by the coesponding time lag and then plotting them togethe with that measued at AV43, eflections fom the left hand side of AV43 ae ovelapped while eflections fom the othe diection ae not, consequently enabling an identification of the diectional souce of the eflection The eflection R5 is fom a known featue, the thicke-walled section between C m and C 1584 m, and it aligns with Case S3 as in Figue 3(c). The maximum dimensionless head petubation fo R5 is ead as.54 fom Figue 9. Using the look-up chat given in Figue 5, the elative change in equivalent steel thickness is detemined as.195. Using Eq. (1) and e = 6.5 mm fo the MTP, the 39 equivalent steel thickness fo this thicke-walled section is detemined as e = 7.47 mm. Using Eq. (6) R and e C = 1.5 mm fo the MTP, the thickness of the steel wall fo the thicke-walled section is 39 detemined as e R5 S1 = 5.98 mm. This esult is smalle than the steel wall thickness given by the manufactue fo this section (which was 6.35 mm) and the ultasonic measuement (6.1 to 6.5 mm). The discepancy is believed to be caused by the inaccuacy of the estimated magnitude of the dimensionless head petubation fo R5 and the damping of the tansient pessue wave The MTP is an above gound pipe and no significant extenal wall deteioation was obseved duing the testing fo the pipe section unde study. As a esult, the eflections R1 to R4, R6 and R7 ae believed to be associated with pipe sections with intenal changes in wall thicknesses. In eal MSCL pipelines, the intenal wall deteioation is moe complex than the situation discussed in the numeical study [Cases S1 and S as shown in Figue 3(a) and (b)]. The deteioation of CML mainly includes cacking, de-bonding, and spalling, and the distibution of deteioation is not unifom aound the intenal cicumfeence. This 5

28 has been confimed by the CCTV camea footage obtained fo the MTP and photo evidence has been included in Stephens et al 36. Afte spalling of the CML, intenal coosion may stat on the steel wall. The sizes of the dimensionless eflections ae compaed with the theshold that epesents unifom total CML loss (dashed line in Figue 9).. Reflections R1, R4, R6 and R7 ae geate than the theshold so that they ae believed to be indications of lage scale CML loss togethe with consideable intenal coosion of the steel wall. Reflections R and R3 ae significant but haven t eached the theshold, so that they ae indications of consideable de-bonding and spalling of the CML and likely to be associated with localised intenal coosion To quantify the deteioation, the look-up chat in Figue 4 is used to detemine the epesentative wall thickness (the emaining wall thickness unde unifom wall deteioation assumption). Sections associated with eflections R1, R4, R6 and R7 ae equivalent to sections with total CML loss and unifom thinning of the steel wall (Case S ), in which the epesentative emaining steel wall thicknesses ae detemined 414 as e R1 S1 = 4.34 mm, e R4 S1 = 4.5 mm, e R6 S1 = 3.76 mm and e R7 S1 = 4.6 mm, espectively. Note that the esults ae only the epesentative steel wall thicknesses (based on the assumption of unifom deteioation ) and the thicknesses in some patches can be smalle than the epesentative values. Because the damping of the tansient wave (which educes the magnitude of wave eflections) is appoximately popotional to the distance tavelled by the wave, and the eflections R1 to R4 ae esulting fom sections moe than 1 km away fom the measuement point (AV43), the condition of these sections is likely to be wose than the epesentative conditions as detemined by using the obseved magnitudes of the eflections Oveall, the condition of the pipe, as detemined by applying the poposed technique, is geneally consistent with the ultasonic esults of the steel wall thickness. Six pipe sections with significant intenal wall deteioation ae identified by using the dimensionless head petubation tace and the epesentative steel wall thicknesses ae detemined by the look-up chats. The case study demonstates that the 6

29 45 46 poposed pipeline condition assessment technique can be used fo non-invasive condition assessment fo cement mota lined pipes in the field. 47 Limitations and challenges The poposed pipeline condition assessment technique has been poven to be useful but it has its limitations and some challenges ae expected in the field. This time-domain technique diectly maps the magnitude of a wave eflection to the wall thickness, which makes the technique efficient and easy to use, but also limits its application to the intepetation of selected significant wave eflections only. In contast, the invese tansient analysis (ITA) is much moe complex to apply, but it can povide infomation fo the whole section of pipe unde test and to a much highe esolution Intenal and extenal changes in wall thickness ae analysed sepaately in this eseach and equations that descibe the elationship between a wave eflection and an intenal o extenal change in wall thickness have been deived espectively. oweve, fom a measued tansient pessue tace, it is difficult to tell if a eflection is due to an intenal o an extenal change in wall thickness. Without additional infomation, the opeato has to estimate the wall thicknesses fo diffeent scenaios. If pioi infomation is available (fo example, fom visual inspections of an above gound pipe), the opeato can fistly detemine the most likely wall deteioation scenaio and then choose the coesponding look-up chat fo the estimation of the emaining wall thickness The accuacy of the look-up chat based technique poposed in this pape elies on the accuate detemination of the wave speed fo the intact pipe ( a ) and the magnitude of the dimensionless head petubation as induced by the deteioated section. In eal pipelines, the detemined a may have uncetainties since some physical popeties of the pipeline may be unknown; deteioation is moe likely to be non-unifom; multiple deteioated sections can intoduce ovelapped complex eflections; and the 7

30 tansmission of the tansient pessue wave is subject to signal dissipation and dispesion. These pactical challenges make the accuate estimation of the dimensionless head petubation difficult. Povided the dimensionless head petubation is detemined with acceptable accuacy, the wall thickness as obtained fom the look-up chat is the epesentative wall thickness that indicates the oveall condition of the deteioated section. Localised infomation about wall thickness, such as the emaining steel thickness of a coosion pit, is unable to be detemined The shapness of the incident pessue wave is impotant 4, but the geneation of a shap and clean step tansient incident pessue wave in eal pipelines is a challenge. In the case study epoted in this pape, a ball valve-based side-dischage valve was connected to the downsteam of a scou valve to act as the tansient geneato and the closing time was typically less than 1 ms 36. As a esult, the geneated incident pessue wave was shap and the pessue oscillation in the scou valve chambe damped out in less than 3 ms. oweve, in cases whee the geneato cannot be connected to the main pipe closely but via a elatively long stand pipe (e.g. seveal metes), the pessue oscillations in the stand pipe afte the valve closue can be significant and pesist fo a longe time (hundeds of milliseconds), which impedes the analysis of the measued tansient pessue signal fo that time peiod. If the side-dischage valve is not closed quickly enough so that the wave font is not as shap as the step wave used in the numeical analysis, the eflections fom the deteioation will not be shap eithe. This may lead to eo in the detemination of the emaining wall thickness of a deteioated section if the length of the section is shote than Ta /, whee T is the ise time of the wave font. A numeical study pesented in Gong et al. 9 exploes how the shapness of a wave font affects the accuacy of the analysis Despite the limitations and challenges, the poposed technique is efficient and applicable to condition assessment of cement mota lined pipes in the field. The accuacy of the detemination of the wall 8

31 thickness can be impoved in the futue if techniques ae developed to compensate the effects of multiple eflections and signal damping. 471 Conclusions A new technique has been developed in this pape fo the condition assessment of cement mota lined pessuised pipes. The condition assessment is achieved by time-domain analysis of the tansient pessue wave eflections measued at existing access points along a pipeline, such as ai valves. The elationship between a change in wall thickness (eithe intenal o extenal) in a cement mota lined metallic pipe and the size of the wave eflection has been deived analytically fo the fist time. As a esult, plots can be dawn to descibe the elationship fo any specific pipeline and these plots can seve as look-up chats fo tansient-based pipeline condition assessment. Numeical simulations have been conducted to veify the validity of the analytical findings. A case study has been conducted on a section of mild steel cement mota lined (MSCL) wate main in South Austalia to illustate how to apply the poposed technique to field data and also veify its applicability. The dimensionless head petubation tace as measued at an ai valve has been plotted and analysed. A theshold value, which epesents the dimensionless head petubation that would be induced by a section of pipe with total loss of the cement mota lining, is used to facilitate evaluation of the significance of the wave eflections. Seven significant tansient eflections have been identified and analysed, with one fom a known thicke-walled section and the othe six fom sections with consideable intenal wall deteioation. The eflection fom the known featue and the fou eflections that have magnitudes geate than the theshold ae futhe analysed using the look-up chat to detemine the epesentative thicknesses of the steel wall. The esults ae geneally consistent with the ultasonic measuements This technique is non-invasive as fluid tansient waves ae used as the tool fo the detection of defects. This technique is also efficient as look-up chats ae used and no inteactive calculation is involved. The 9

32 poposed technique enables on-site tansient-based condition assessment fo cement mota line metallic pipes, which is cost-effective and contibutes to stategic maintenance of citical pipeline assets. 494 Acknowledgements The eseach pesented in this pape has been suppoted by the Austalian Reseach Council though the Linkage Poject Gant LP Appendix Justification of the total equivalent steel wall thickness (equivalent steel thickness) as defined in Eq. (6) and used in Eq. (7) 5 51 Fo a pessue wave popagating inside a fictionless pipe with unifom coss section, classic one- dimensional wate hamme theoy gives the geneal wave speed fomula as 8 a K / 1 ( K / A)( A / p) (A1) 5 53 whee pessue A is the vaiation of the coss-sectional aea of the pipe caused by the vaiation of the wate p. Fo a thin-walled steel pipe with thin-walled cement mota lining, the change in tensile 54 stess in the steel wall and in the cement mota lining, S and C espectively as illustated in 55 Figue A1, ae elated to the change in adial foce induced by p, whee the elationship is / SeS CeC pd (A) 3

33 Steel wall Cement mota lining Figue A1. Foces on semicylinde of pipe due to vaiation in pessue Assuming the cement mota lining is closely bonded with the steel wall so that the change in cicumfeential unit stain is the same in both layes, ignoing the change in axial tensile stess and applying ooke s law to Eq. (A), the change in cicumfeential unit stain can be witten by pd ECeC ESeS (A3) 511 The adial extension is obtained by multiplying by the adius D /, which, when multiplied by 51 D, yields the change in coss sectional-aea A. As a esult, the following equation is deived: A D Ap E e E e (A4) C C S S 513 Substituting Eq. (A4) into Eq. (A1) and applying mathematical manipulation, the wave speed is given by 31

34 a K / 1 ( K / E )( D / e ) S (A5) 514 whee e is the total equivalent steel wall thickness (equivalent steel thickness) as defined by Eq. (6). If 515 e = (no steel wall) and e C = (no cement lining), Eq. (A5) becomes the commonly seen geneal S wave speed fomula fo unifom mateial thin-walled elastic pipe. If E S o E C eaches infinity, Eq. (A5) becomes a K /, which is the acoustic speed of a small distubance in an infinite fluid If the change in axial tensile stess is consideed, the Poisson s atio can be used to descibe the elationship between the cicumfeential stain and the axial stain. Assuming that the Poisson s atios ae the same fo steel and cement, Eq. (7) can be deived Refeences Jo BY, Laven K and Jacob B. Advances in CCTV technology fo in-sevice wate mains. Pipelines 1: Climbing New Peaks to Infastuctue Reliability - Renew, Rehab, and Reinvest, August 8, 1 - Septembe 1, 1. Keystone, CO, United states: Ameican Society of Civil Enginees, 1, p Gimes J and De Alvaez AN. Utilizing cicumfeential MFL fo the detection of linea and axially oiented metal loss anomalies in pipelines. 8 ASME Intenational Pipeline Confeence, IPC 8, Septembe 9, 8 - Octobe 3, 8. Calgay, AB, Canada: Ameican Society of Mechanical Enginees, 9, p Ekes C, Neducza B and enich GR. Completing condition assessments using in-pipe GPR as pipe penetating ada. Pipelines 11: A Sound Conduit fo Shaing Solutions. Seattle, WA, United States: ASCE, 11, p Paulson P and Nguyen V. Pipe wall evaluation using acoustic pulses. Pipelines 1: Climbing New Peaks to Infastuctue Reliability - Renew, Rehab, and Reinvest, August 8, 1 - Septembe 1, 1. Keystone, CO, United states: Ameican Society of Civil Enginees, 1, p Lowe MJS, Alleyne DN and Cawley P. Defect detection in pipes using guided waves. Ultasonics. 1998; 36: Liu Z and Kleine Y. State of the at eview of inspection technologies fo condition assessment of wate pipes. Measuement. 13; 46: Chaudhy M. Applied ydaulic Tansients. 3d ed. New Yok, NY: Spinge, 14. 3