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Abstract:Spraying polyurethane elastomers used as insulation and waterproof coating were prepared by the rotary spraying process without mold.The water absorp-tion,thermal conductivity,density and water pressure of the traditional thermal insulation materials were compared with that of the spraying polyurethane elastomers in the experiment.Also the experiments of heat insulating properties in deep-sea were done.The results show that the spraying polyurethane elastomers can meet the heat insu-lating requirements of submarine oil pipelines in the depth more than500m.
Key words:oil pipelines;polyurethane elastomers;insulation and waterproof;spraying process
1Introduction
The oil and gas resources in the deep-sea are greatly different from that on the land.Submarine pipelines are in the environment of cold sea-water.When the oil temperature drops to a certain value,it will precipitate high molecular crude wax,resulting in oil viscosity increased.Even the problem of pipeline congestion will occur[1-2].Therefore,it is necessary to carry on the effective heat insulating processing to the submarine oil pipeline,in order to guarantee the pipeline's nor-mal operation.
The rotary spraying polyurethane elastomers without mold are developed based on the process of molded polyurethanes.By multilayer coating,it can meet the requirement of design thickness,even mechanical(such as tear method)andoptical(SEM)methods are difficult to separate the bonding layers[3].The rotary spraying polyurethane elastomers have the advantages of strong adhesive,uniform coverage,low density,small thermal conductivity,low temperature and low water absorption[4].So the continuous improvement of research on the performance of spraying polyurethane elastomers as heat insulating material of submarine oil pipelines has important practical significance to the exploitation of oil and gas re-sources.
2Experiment
2.1 Materials and equipments
Component A of polyurethane prepolymer was obtained by mixing1,5-naphthalene diisocyanate(NDI)and chain extender ethylenediamine(EDA),while component B of polyurethane was obtained by mixing polytetramethylene ether glycol(PTMG),polybutylene adipate(PBA)and a small amount of1,4-bu-tanediol(BDO).The proportion of PBA,PTMG and NDI is65:35:50.The material of pipeline(Φ1000mm,σ=3mm)and samples(40mm×40mm,10mm×10mm)is30CrMnSiNi2A steel.Experimental equipment mainly includes:Portable two-component cartridge spray gun;ESC75type compressor;Self-adjusting roller frame of spraying. 2.2 Samples preparation
Adjust the parameters of air compressor,as well as the speed and position of roller frame,to keep the spray gun perpendicular to the tangential direction of pipeline.Spraying distance and speed should be detected all the time to maintain constant.Parameters of spraying process:Temperature(30℃),Pressure(0.74MPa),Distance(200-300mm),Linear velocity(300-400mm/min),Thickness of each layer(50-60μm).
3Test and analysis of performance
3.1Physical properties
Because of the harsh environment of the temperature distribution,hydrostatic pressure and saline stress corrosion,it must meet the following performance:①high compressive strength and elasticity to withstand hydrostatic pressure of sea-water;②small thermal conductivity and performance of resistance to low temper-ature;③low water absorption and better waterproof to ensure pipeline from sea-water corrosion.
Polyurethane foam have the advantages of small thermal conductivity and low density,but because of its low strength and low anti-static pressure limiting the application range,it is often used in land oil and gas pipelines and submarine pipelines in depth less than50m.Compared with the molded glass bead compos-ite polyurethane,the preparation process of spraying polyurethane elastomers is simple,and it is easy to control the quality,avoiding the tedious process of mold and curing box.
3.2The performance of insulation of spraying polyurethane in the environ-ment of deep-sea
The temperature,pressure,salinity and velocity of seawater of deep-sea are greatly different from that of sea surface,and temperature drops very fast under the sea surface of300m initially.In the water depth of about350m there is a con-stant temperature layer,with the depth of the increasing,the water temperature drops slowly.Hydrostatic pressure increases by about1MPa with the depth in-creasing by every100m[5].Table1shows distribution of temperature,pressure and salinity under different water depth[6-7].
Table1Distribution of temperature,pressure and salinity under different water depth
Fig.1Heat loss rate of spraying polyurethane under different water depth
Fig.1illustrates that in the sea area of depth of30~500m,heat loss rate ofspraying polyurethane are less than the value required.In the shallow waters of depth of30~60m,the temperature of sea water is higher(about8℃),the heat loss rate of polyurethane is more instead,and it’s about2.9W?m-2?k-1.The reason for this result is that the ocean surface current is faster than that of deeper layer,thus speeding up the convective heat exchange between the sea and the insulation coating surface,so that heat loss rate increases.In the deep waters of depth of300~500m,the temperature is lower(about2℃).Since difference in temperature between water and heat insulating coating is large,and heat radiation and con-duction are also relatively large,leading to heat loss rate of polyurethane in-creased.But it is still less than the required value of3W?m-2?k-1,this is mainly due to low thermal conductivity of0.095~0.115W?m-2?k-1and low water ab-sorption rate of1.5~2.5mg?cm-3of Spraying polyurethane elastomers,ensuring the heat insulating of polyurethane in the environment of deep-sea. 4Conclusions
Spraying polyurethane elastomers were prepared by the rotary spraying pro-cess without mold,and the proportion of PBA,PTMG and NDI is65:35:50.The physical performance of low thermal conductivity,low water absorption and high strength,as well as low heat loss rate in the environment of deep-sea,can meet the heat insulating requirements of submarine oil pipelines in the depth more than500m.
References
[1]Xiao-bing Jiang,Zhengle Xiang.Present Situation of Thermal Insulation Material for Deep water Pipeline[J].Pipe line Technique and Equipment,2010,6(3):47-50.
[2] Zhi-yong Hu,Ming Wu.Research on Wax Deposition in Thermal Insula-tion Oil Pipeline[J].Contemporary Chemical Industry,2013,49(6):1312-1315.
[3] Ying-tao Wu.Status and development of thermal insulation pipeline[J].Polyurethane Industry Association,2008,1:291-297.
[4] Xiao-juan Lai,Yi-ding Shen,Lei Wang.Structure and properties of dou-ble crosslinking waterborne polyurethane[J].Journal of Functional Materials,2011,5(42):940-943.
[5] Rosalind A,Michael J Sullivan.Models for heat transfer from a buried pipe[J].SPE Journal,1997,2(2):186-193.
[6] Vedenee D E.Combined thermal-momentum start-up in long pipes[J].Journal of Heat and Mass Transfer,1990,33(9):2051-2053.
[7] Xu-lin Yang,Li-qi Chen.Characteristics of salinity distribution in surface seawater of the oceans[J].Journal of Oceanography in Taiwan Strait,1990,9(1):88-91.
Key words:oil pipelines;polyurethane elastomers;insulation and waterproof;spraying process
1Introduction
The oil and gas resources in the deep-sea are greatly different from that on the land.Submarine pipelines are in the environment of cold sea-water.When the oil temperature drops to a certain value,it will precipitate high molecular crude wax,resulting in oil viscosity increased.Even the problem of pipeline congestion will occur[1-2].Therefore,it is necessary to carry on the effective heat insulating processing to the submarine oil pipeline,in order to guarantee the pipeline's nor-mal operation.
The rotary spraying polyurethane elastomers without mold are developed based on the process of molded polyurethanes.By multilayer coating,it can meet the requirement of design thickness,even mechanical(such as tear method)andoptical(SEM)methods are difficult to separate the bonding layers[3].The rotary spraying polyurethane elastomers have the advantages of strong adhesive,uniform coverage,low density,small thermal conductivity,low temperature and low water absorption[4].So the continuous improvement of research on the performance of spraying polyurethane elastomers as heat insulating material of submarine oil pipelines has important practical significance to the exploitation of oil and gas re-sources.
2Experiment
2.1 Materials and equipments
Component A of polyurethane prepolymer was obtained by mixing1,5-naphthalene diisocyanate(NDI)and chain extender ethylenediamine(EDA),while component B of polyurethane was obtained by mixing polytetramethylene ether glycol(PTMG),polybutylene adipate(PBA)and a small amount of1,4-bu-tanediol(BDO).The proportion of PBA,PTMG and NDI is65:35:50.The material of pipeline(Φ1000mm,σ=3mm)and samples(40mm×40mm,10mm×10mm)is30CrMnSiNi2A steel.Experimental equipment mainly includes:Portable two-component cartridge spray gun;ESC75type compressor;Self-adjusting roller frame of spraying. 2.2 Samples preparation
Adjust the parameters of air compressor,as well as the speed and position of roller frame,to keep the spray gun perpendicular to the tangential direction of pipeline.Spraying distance and speed should be detected all the time to maintain constant.Parameters of spraying process:Temperature(30℃),Pressure(0.74MPa),Distance(200-300mm),Linear velocity(300-400mm/min),Thickness of each layer(50-60μm).
3Test and analysis of performance
3.1Physical properties
Because of the harsh environment of the temperature distribution,hydrostatic pressure and saline stress corrosion,it must meet the following performance:①high compressive strength and elasticity to withstand hydrostatic pressure of sea-water;②small thermal conductivity and performance of resistance to low temper-ature;③low water absorption and better waterproof to ensure pipeline from sea-water corrosion.
Polyurethane foam have the advantages of small thermal conductivity and low density,but because of its low strength and low anti-static pressure limiting the application range,it is often used in land oil and gas pipelines and submarine pipelines in depth less than50m.Compared with the molded glass bead compos-ite polyurethane,the preparation process of spraying polyurethane elastomers is simple,and it is easy to control the quality,avoiding the tedious process of mold and curing box.
3.2The performance of insulation of spraying polyurethane in the environ-ment of deep-sea
The temperature,pressure,salinity and velocity of seawater of deep-sea are greatly different from that of sea surface,and temperature drops very fast under the sea surface of300m initially.In the water depth of about350m there is a con-stant temperature layer,with the depth of the increasing,the water temperature drops slowly.Hydrostatic pressure increases by about1MPa with the depth in-creasing by every100m[5].Table1shows distribution of temperature,pressure and salinity under different water depth[6-7].
Table1Distribution of temperature,pressure and salinity under different water depth
Fig.1Heat loss rate of spraying polyurethane under different water depth
Fig.1illustrates that in the sea area of depth of30~500m,heat loss rate ofspraying polyurethane are less than the value required.In the shallow waters of depth of30~60m,the temperature of sea water is higher(about8℃),the heat loss rate of polyurethane is more instead,and it’s about2.9W?m-2?k-1.The reason for this result is that the ocean surface current is faster than that of deeper layer,thus speeding up the convective heat exchange between the sea and the insulation coating surface,so that heat loss rate increases.In the deep waters of depth of300~500m,the temperature is lower(about2℃).Since difference in temperature between water and heat insulating coating is large,and heat radiation and con-duction are also relatively large,leading to heat loss rate of polyurethane in-creased.But it is still less than the required value of3W?m-2?k-1,this is mainly due to low thermal conductivity of0.095~0.115W?m-2?k-1and low water ab-sorption rate of1.5~2.5mg?cm-3of Spraying polyurethane elastomers,ensuring the heat insulating of polyurethane in the environment of deep-sea. 4Conclusions
Spraying polyurethane elastomers were prepared by the rotary spraying pro-cess without mold,and the proportion of PBA,PTMG and NDI is65:35:50.The physical performance of low thermal conductivity,low water absorption and high strength,as well as low heat loss rate in the environment of deep-sea,can meet the heat insulating requirements of submarine oil pipelines in the depth more than500m.
References
[1]Xiao-bing Jiang,Zhengle Xiang.Present Situation of Thermal Insulation Material for Deep water Pipeline[J].Pipe line Technique and Equipment,2010,6(3):47-50.
[2] Zhi-yong Hu,Ming Wu.Research on Wax Deposition in Thermal Insula-tion Oil Pipeline[J].Contemporary Chemical Industry,2013,49(6):1312-1315.
[3] Ying-tao Wu.Status and development of thermal insulation pipeline[J].Polyurethane Industry Association,2008,1:291-297.
[4] Xiao-juan Lai,Yi-ding Shen,Lei Wang.Structure and properties of dou-ble crosslinking waterborne polyurethane[J].Journal of Functional Materials,2011,5(42):940-943.
[5] Rosalind A,Michael J Sullivan.Models for heat transfer from a buried pipe[J].SPE Journal,1997,2(2):186-193.
[6] Vedenee D E.Combined thermal-momentum start-up in long pipes[J].Journal of Heat and Mass Transfer,1990,33(9):2051-2053.
[7] Xu-lin Yang,Li-qi Chen.Characteristics of salinity distribution in surface seawater of the oceans[J].Journal of Oceanography in Taiwan Strait,1990,9(1):88-91.