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Flow assurance integrity issues
C H A P T E R
9 Flow assurance integrity issues O U T L I N E Corrosion Introduction Types of corrosion Corrosion monitoring methods Currently used corrosion control techniques
217 217 218 218
Integrated models
219
Erosion
220
References
220
219
Corrosion Introduction Besides mechanical impacts on pipe walls and process equipment by liquid slugs and moving flow assurance plug projectiles, the production system also experiences chemical degradation by corrosion. Corrosion management is the domain of corrosion engineers. Corrosion system design should be done in collaboration with flow assurance specialists. Numerous flow parameters which are used to estimate the rate of corrosion can be derived from flow assurance analysis, including: multiphase flow regime, liquid and gas flow velocities and densities, liquid and gas pressure and temperature, rate of liquid droplets entrainment by gas flow, location and rate of water condensation from gas, location and composition of water holdup, shear stress exerted by gas or liquid flow on the pipe wall, flow velocities at the chemical injection quill locations, locations of solid deposits.
Handbook of Multiphase Flow Assurance https://doi.org/10.1016/B978-0-12-813062-9.00009-9
217
© 2019 Elsevier Inc. All rights reserved.
218
9. Flow assurance integrity issues
Types of corrosion A large amount of NACE literature on corrosion exists. General details on corrosion are available (Fontana 1975; Dillon 1982). Two key categories of corrosion are: physico-chemical corrosion. microbially influenced corrosion. Some of the common types of physico-chemical corrosion include: Uniform—caused by electrochemical reaction leading to dissolution of metal; Galvanic—may occur due dissimilar weld material and pipe material; Pitting—localized corrosion enhanced by localized difference in ion concentration; Crevice—when a gap between pipe wall and another material such as flow assurance deposit creates a localized difference in ion concentration; Intergranular—when metallurgy has dissimilar grains of metal present; Stress corrosion cracking—due presence of chloride ions released from fluid. May occur in stainless steels such as chemical injection systems or sour service systems (Fischer et al., 2016). Hydrogen embrittlement—may occur due hydrogen evolution in the system and ingress into metals due to its small molecule size. Microbially influenced corrosion (MIC) affects the rate of corrosion processes due to a biofilm formation on a surface of pipe. MIC may occur in crude pipelines near the locations of water holdup in low spots, which relates the MIC to flow assurance hydraulic analysis. A recent overview of MIC in petroleum systems is provided by Al-Saleh et al. (2011).
Corrosion monitoring methods There are several methods in the operations to monitor corrosion rate listed: Weight loss coupons. Electrical resistance probes. Linear polarization resistance (LPR). Field signature method (FSM). Electrochemical noise. Flexible UT Mats. Ultrasonic pipe thickness measurement. ILI in-line inspection with magnetic flux leakage intelligent scraper tool. Radioactive methods. Indirect monitoring may also be done by Ultrasonic sand detection. Process stream analysis. Corrosion monitoring can provide data for tuning of the integrated multiphase flow and corrosion models. An overview summary of corrosion monitoring methods is available in Hedges and Bodington (2004).
Corrosion
219
Currently used corrosion control techniques Corrosion prevention is accomplished by several methods simultaneously: use of corrosion inhibitor chemicals, use of maintenance scraping to remove water holdup from the pipelines, use of corrosion-resistant materials. Corrosion inhibitor chemicals are among the most widely used methods of corrosion methods. Chemicals performance is evaluated in laboratory by tests and in field by in-line inspection. Lab methods aim to measure: Inhibitor efficiency; Inhibitor partitioning behavior between hydrocarbon and water; Compatibility with other production chemicals; Film stability and persistence; Optimum concentration. Inhibitor efficiency may be measured with: Bubble test apparatus; Rotating electrode, including rotating disk (laminar flow) and rotating cylinder (turbulent flow, high shear); Jet impingement test; Recirculating flow loop, which allows to make tests at a controlled shear stress; In-line inspection (ILI) uses magnetic flux leakage probes installed circumferentially on a ILI tool which records wall thickness along the whole perimeter and length of the tested pipe.
Integrated models Multiphase flow models can be combined with corrosion rate models to provide an integrated assessment of the expected corrosion rates for a given flow scenario. There are commercial tools available which allow to estimate corrosion rate. Alternatively it is possible to find multiphase flow parameters and then use these in the corrosion rate prediction model. Commercial multiphase flow simulators have modules of published corrosion models such as NORSOK M-506, deWaard-95 and Top-Of-the-LineCorrosion (Wang and Nesic, 2003). The first two are for CO2 based corrosion, and the TOLC is for condensed fresh water corrosion. The use of these built-in modules for corrosion rate assessment may be limited if corrosion engineers at operator companies develop and maintain in-house corrosion rate prediction models. The limitation for the use of multiphase tools’ corrosion modules for corrosion rate prediction is the limited ability to tune the model input parameters. It may be useful as an initial check of the corrosion rate. Nonetheless, multiphase flow modeling tools are very useful and indispensable in analyzing the two parameters which are required by the corrosion specialists: thermal conditions of flowing fluids and shear rates exerted by fluids on pipe wall. Both of these are parameters used in the in-house models. Temperature determines both the corrosive species’ diffusion and corrosion reaction rate and the condensation rate of fresh water. Shear affects the corrosion inhibitor layer and the protective corrosion product layer. Some operators, to derive the desired shear and temperature distribution, as well as flow regime, attempt to couple the in-house corrosion rate
220
9. Flow assurance integrity issues
correlations with multiphase flow models such as point or drift flux slip, with varying success. The uncertainty in corrosion rate prediction keeps the ILI inspection service companies in demand. In some instances, best available in-house models for US-based and UK-based integrated operators underpredicted the corrosion rate in deepwater dense fluid production and in onshore sour service production. Other companies deploy artificial intelligence to fit measured rates to corrosion models. Comparison of which flow parameters (calculated with a commercial multiphase flow simulator) have the most impact showed that holdup and inside heat transfer were top (Liao et al., 2012).
Erosion Besides mechanical degradation of pipe wall surface, erosion by impingement of liquid droplets or solids such as sand or hydrates affects the integrity of the protective corrosion inhibitor film or of a corrosion product layer formed on a passivated pipe wall. This may lead to localized pitting corrosion.
References Al-Saleh, M.A., Sanders, P.F., Ibrahim, T.M., Sorensen, K.B., Lundgaard, T., Juhler, S., 2011. Microbially influenced corrosion assessment in crude oil pipelines. In: NACE-11227, Corrosion-2011, 13–17 March, Houston. Dillon, C.P. (Ed.), 1982. Forms of Corrosion, Recognition and Prevention. Vol. 7. NACE. Fischer, D., Li, C., Huang, W., Sun, W., 2016. Investigation of the sulfide stress cracking and stress corrosion cracking behaviors of duplex and lean duplex stainless steel parent and welded materials in sour service. In: NACE-20167325, Corrosion 2016, 6–10 March, Vancouver. Fontana, M.G., 1975. The Eight Forms of Corrosion, Process Industries Corrosion. NACE, pp. 1–39. Hedges, W., Bodington, A., 2004. A comparison of monitoring techniques for improved erosion control: a field study. In: NACE-04355, Corrosion 2004, 28 March-1 April, New Orleans. Liao, K., Yao, Q., Wu, X., Jia, W., 2012. A numerical corrosion rate prediction method for direct assessment of wet gas gathering pipelines internal corrosion. Energies 5, 3892–3907. Wang, S., Nesic, S., 2003. On coupling CO2 corrosion and multiphase flow models. In: Paper 03631, Corrosion 2003, NACE International.
9 Flow assurance integrity issues O U T L I N E Corrosion Introduction Types of corrosion Corrosion monitoring methods Currently used corrosion control techniques
217 217 218 218
Integrated models
219
Erosion
220
References
220
219
Corrosion Introduction Besides mechanical impacts on pipe walls and process equipment by liquid slugs and moving flow assurance plug projectiles, the production system also experiences chemical degradation by corrosion. Corrosion management is the domain of corrosion engineers. Corrosion system design should be done in collaboration with flow assurance specialists. Numerous flow parameters which are used to estimate the rate of corrosion can be derived from flow assurance analysis, including: multiphase flow regime, liquid and gas flow velocities and densities, liquid and gas pressure and temperature, rate of liquid droplets entrainment by gas flow, location and rate of water condensation from gas, location and composition of water holdup, shear stress exerted by gas or liquid flow on the pipe wall, flow velocities at the chemical injection quill locations, locations of solid deposits.
Handbook of Multiphase Flow Assurance https://doi.org/10.1016/B978-0-12-813062-9.00009-9
217
© 2019 Elsevier Inc. All rights reserved.
218
9. Flow assurance integrity issues
Types of corrosion A large amount of NACE literature on corrosion exists. General details on corrosion are available (Fontana 1975; Dillon 1982). Two key categories of corrosion are: physico-chemical corrosion. microbially influenced corrosion. Some of the common types of physico-chemical corrosion include: Uniform—caused by electrochemical reaction leading to dissolution of metal; Galvanic—may occur due dissimilar weld material and pipe material; Pitting—localized corrosion enhanced by localized difference in ion concentration; Crevice—when a gap between pipe wall and another material such as flow assurance deposit creates a localized difference in ion concentration; Intergranular—when metallurgy has dissimilar grains of metal present; Stress corrosion cracking—due presence of chloride ions released from fluid. May occur in stainless steels such as chemical injection systems or sour service systems (Fischer et al., 2016). Hydrogen embrittlement—may occur due hydrogen evolution in the system and ingress into metals due to its small molecule size. Microbially influenced corrosion (MIC) affects the rate of corrosion processes due to a biofilm formation on a surface of pipe. MIC may occur in crude pipelines near the locations of water holdup in low spots, which relates the MIC to flow assurance hydraulic analysis. A recent overview of MIC in petroleum systems is provided by Al-Saleh et al. (2011).
Corrosion monitoring methods There are several methods in the operations to monitor corrosion rate listed: Weight loss coupons. Electrical resistance probes. Linear polarization resistance (LPR). Field signature method (FSM). Electrochemical noise. Flexible UT Mats. Ultrasonic pipe thickness measurement. ILI in-line inspection with magnetic flux leakage intelligent scraper tool. Radioactive methods. Indirect monitoring may also be done by Ultrasonic sand detection. Process stream analysis. Corrosion monitoring can provide data for tuning of the integrated multiphase flow and corrosion models. An overview summary of corrosion monitoring methods is available in Hedges and Bodington (2004).
Corrosion
219
Currently used corrosion control techniques Corrosion prevention is accomplished by several methods simultaneously: use of corrosion inhibitor chemicals, use of maintenance scraping to remove water holdup from the pipelines, use of corrosion-resistant materials. Corrosion inhibitor chemicals are among the most widely used methods of corrosion methods. Chemicals performance is evaluated in laboratory by tests and in field by in-line inspection. Lab methods aim to measure: Inhibitor efficiency; Inhibitor partitioning behavior between hydrocarbon and water; Compatibility with other production chemicals; Film stability and persistence; Optimum concentration. Inhibitor efficiency may be measured with: Bubble test apparatus; Rotating electrode, including rotating disk (laminar flow) and rotating cylinder (turbulent flow, high shear); Jet impingement test; Recirculating flow loop, which allows to make tests at a controlled shear stress; In-line inspection (ILI) uses magnetic flux leakage probes installed circumferentially on a ILI tool which records wall thickness along the whole perimeter and length of the tested pipe.
Integrated models Multiphase flow models can be combined with corrosion rate models to provide an integrated assessment of the expected corrosion rates for a given flow scenario. There are commercial tools available which allow to estimate corrosion rate. Alternatively it is possible to find multiphase flow parameters and then use these in the corrosion rate prediction model. Commercial multiphase flow simulators have modules of published corrosion models such as NORSOK M-506, deWaard-95 and Top-Of-the-LineCorrosion (Wang and Nesic, 2003). The first two are for CO2 based corrosion, and the TOLC is for condensed fresh water corrosion. The use of these built-in modules for corrosion rate assessment may be limited if corrosion engineers at operator companies develop and maintain in-house corrosion rate prediction models. The limitation for the use of multiphase tools’ corrosion modules for corrosion rate prediction is the limited ability to tune the model input parameters. It may be useful as an initial check of the corrosion rate. Nonetheless, multiphase flow modeling tools are very useful and indispensable in analyzing the two parameters which are required by the corrosion specialists: thermal conditions of flowing fluids and shear rates exerted by fluids on pipe wall. Both of these are parameters used in the in-house models. Temperature determines both the corrosive species’ diffusion and corrosion reaction rate and the condensation rate of fresh water. Shear affects the corrosion inhibitor layer and the protective corrosion product layer. Some operators, to derive the desired shear and temperature distribution, as well as flow regime, attempt to couple the in-house corrosion rate
220
9. Flow assurance integrity issues
correlations with multiphase flow models such as point or drift flux slip, with varying success. The uncertainty in corrosion rate prediction keeps the ILI inspection service companies in demand. In some instances, best available in-house models for US-based and UK-based integrated operators underpredicted the corrosion rate in deepwater dense fluid production and in onshore sour service production. Other companies deploy artificial intelligence to fit measured rates to corrosion models. Comparison of which flow parameters (calculated with a commercial multiphase flow simulator) have the most impact showed that holdup and inside heat transfer were top (Liao et al., 2012).
Erosion Besides mechanical degradation of pipe wall surface, erosion by impingement of liquid droplets or solids such as sand or hydrates affects the integrity of the protective corrosion inhibitor film or of a corrosion product layer formed on a passivated pipe wall. This may lead to localized pitting corrosion.
References Al-Saleh, M.A., Sanders, P.F., Ibrahim, T.M., Sorensen, K.B., Lundgaard, T., Juhler, S., 2011. Microbially influenced corrosion assessment in crude oil pipelines. In: NACE-11227, Corrosion-2011, 13–17 March, Houston. Dillon, C.P. (Ed.), 1982. Forms of Corrosion, Recognition and Prevention. Vol. 7. NACE. Fischer, D., Li, C., Huang, W., Sun, W., 2016. Investigation of the sulfide stress cracking and stress corrosion cracking behaviors of duplex and lean duplex stainless steel parent and welded materials in sour service. In: NACE-20167325, Corrosion 2016, 6–10 March, Vancouver. Fontana, M.G., 1975. The Eight Forms of Corrosion, Process Industries Corrosion. NACE, pp. 1–39. Hedges, W., Bodington, A., 2004. A comparison of monitoring techniques for improved erosion control: a field study. In: NACE-04355, Corrosion 2004, 28 March-1 April, New Orleans. Liao, K., Yao, Q., Wu, X., Jia, W., 2012. A numerical corrosion rate prediction method for direct assessment of wet gas gathering pipelines internal corrosion. Energies 5, 3892–3907. Wang, S., Nesic, S., 2003. On coupling CO2 corrosion and multiphase flow models. In: Paper 03631, Corrosion 2003, NACE International.