Performance of Pipes during Earthquakes

Transcription

1 Performance of Pipes during Earthquakes Camille George Rubeiz, PE Director of Engineering, Plastics Pipe Institute, USA (Presented at the Plastics Pipe XV, Vancouver, BC, Canada, September 20-22, 2010) ABSTRACT This paper summarizes the performance of water and gas piping systems during six earthquakes in the US, Japan, Thailand and Columbia. Also, the paper will present data from the UK and Sweden about the performance of pipes in non-earthquake environments. The paper will assist design engineers and owners in selecting pipe materials based on the past performance of the materials and based on the recommendations from the American Water Works Association and the American Society of Civil Engineers. INTRODUCTION In the US, the lack of a national seismic code for piping systems can or has affected critical municipal, industrial, and energy related pipelines constructed over the last 100 years. Imagine several days or several weeks without clean water, without sewer, or without natural gas, while severed pipelines are being repaired following an earthquake or a tsunami. Most piping systems have not been designed and detailed properly to resist earthquake loads and movements. Most consulting firms are not required by their clients (owners) to address these hazards. This lack of requirements in seismically active or coastal zones may be due to lack of awareness about the effect of these hazards on pipelines, cost issues, performance, damage and other priorities. The low cost of water in the US has played a role in reducing the funding available to design or retrofit piping systems to better withstand earthquake loads. Unlike standards for buildings and other structures (ASCE/SEI 2005; IBC 2006) that require designers and owners to design structures for earthquake loads and movements, standards for pipes (published by AWWA) do not include specific requirements for the design, detailing and/or construction of pipes in seismic regions. Although AWWA and ASCE have published multiple reports on earthquake resistant pipeline design and performance, many pipe designers and owners may not be aware of these resources, or of the potential consequences of earthquakes. This paper highlights the relevant conclusions of these publications and refers readers to the actual publications for full review and implementation in their local design specifications to minimize the effects of these hazards on the local and national hidden pipeline assets. EARTHQUAKE HISTORY IN THE USA In the US, every state has experienced some level of earthquakes as documented on the website of the US Geological Services the site lists the largest recorded earthquake (by magnitude) with epicenter in each state; in some states, the highest intensity of earth shaking occurred from earthquakes in nearby states. A summary of this data is

2 shown in Table I: As of July 2010, the state of Maryland (MD) experienced the lowest magnitude earthquake of 2.6 and the state of Alaska (AK) experienced the highest magnitude earthquake of 9.2. On July 16, 2010, MD experienced a 3.6 earthquake that has not been reported on the USGS website. Seven states did not have a magnitude reported and instead, the note below Table I, lists the Intensity of earth shaking in these states. Table I. Magnitude of Largest Recorded Earthquakes in Each US State, Listed in Order of Smallest to Largest, as of July 2010 (USGS website) MD 2.6 RI 3.5 LA 4.2 VT 4.2 GA 4.5 SD 4.5 WV 4.5 MI 4.6 MN 4.6 MS 4.6 TN 5.0 AL 5.1 IN 5.1 KS 5.1 ME 5.1 NE 5.1 KY 5.2 NC 5.2 PA 5.2 NJ 5.3 IL 5.4 OH 5.4 OK 5.5 NH 5.5 ND 5.5 AZ 5.6 NY 5.8 TX 5.8 VA 5.9 WY 6.5 CO 6.6 UT 6.6 OR 6.8 WA 6.8 ID 6.9 NV 7.2 MT 7.3 SC 7.3 MO ~7.7 AR ~7.7 CA 7.9 HI 7.9 AK 9.2 Note: Some US states had only the intensity reported: MA (VIII), NM (VII), CT (VII), DE (VII), FL (VI), IA (V) and WI (V). According to the National Research Council (NRC 2003), despite popular perceptions that earthquakes are an issue only for the western states, much of the United States is at risk, and major cities in the Midwest and on the East Coast are particularly vulnerable owing to a lack of awareness and preparedness. EARTHQUAKES HISTORY AND EFFECTS ON PIPES In the following section, the paper will review the effects of 6 earthquakes on the performance of water and gas pipes in 4 countries. Damage Mechanisms. In 2006, researchers at Cornell University conducted multiple tests to study the effect of earthquakes on water and gas pipes. The lessons learned could lead to better design practice for lessening impacts and reducing recovery time in the case of catastrophic events. According to a research associate, if a gas pipe breaks during an earthquake it can cause fire, if the nearby water pipe breaks, the ability to control the fire is greatly reduced. Failures in pipelines have often resulted in the failure of the overall water supply system due to rapid loss of water draining the reservoirs; in case of power loss, the reservoirs cannot be refilled and system can remain without water for days. Pipeline failures are highest in areas of ground failure or liquefaction and can occur due to wave propagation, permanent ground deformation and fault rupture as noted below: Wave propagation results in: (AWWA 1994, p ) Lower pipe failures than other mechanisms Bending or joint rotation is minimal

3 In almost all cases, continuous arc welded steel or polyethylene pipe has adequate ductility to accommodate wave propagation ground strains with no damage. Permanent ground deformation results in: (AWWA 1994, p. 41) Higher failure rates than from wave propagation Pipelines fail in bending, shear, tension and compression Partially empty pipelines, primary gravity sewers can float due to liquefaction if the sewer s burial places it within the liquefaction layer. Fault rupture will result in: (AWWA 1994, p. 42) Pipelines crossing faults will shear, or be put in tension or compression Pipelines in the low-vulnerability category will perform the best when fault movement occurs. Pipe damage is influenced by: (ASCE 1999, p. 60) The more ductile the material, the lower the damage rate. However, thin wall ductile material (like ductile iron and steel) is susceptible to corrosion which can offset the benefits of ductility. Rigid joint material (like cement) cause higher damage rates than flexible joint material (rubber gasket). Joint pullout and crushing possible with slip on segmented pipe. Welded steel joints or mechanically locked joints should have better seismic performance than segmented joints. Corrosion on metal pipes increases pipe damage rate. Larger diameter pipes appear to have lower damage rates than smaller small diameter pipe. Deeper burials lower the damage rate. San Francisco Earthquake (ASCE-NPFA, 2005). On April 18, 1906, the city experienced a major earthquake with magnitude of 8.3. All of the city s downtown was destroyed, along with 300 water mains and over 23,000 water services (Van Dyke 1997). Fires burned for 3 days due to lack of water to control them. 28,000 buildings were destroyed and 80% of the damage was due to the fire rather than the seismic shaking. This was the largest earthquake loss in US history which resulted in the death of 3,000 people and the loss of $524 million using 1906 dollars. (Van Dyke 1997). Northridge Earthquake: Effects on Water Pipes (AWWA 1994, ASCE 1999). On January 17, 1994, the city experienced a major earthquake with magnitude of 6.8 and the Peak Ground Acceleration (PGA) exceeded 1g at the epicenter area. The city of Northridge is located about 20 miles from Los Angeles. The quake resulted in damage to the three transmission pipes that deliver water from Northern California. Also, over 1,500 water system pipeline failures occurred in the San Fernando and Santa Clarita valleys (AWWA 1994, p. vii). It was noted that if this earthquake had occurred in other locations in North America, the water system would have been more heavily damaged than was seen in Northridge (AWWA 1994, p viii). The facilities that were exposed to Northridge are owned and operated by utilities that were subjected to the February 9, 1971 San Fernando earthquake (Magnitude 6.7) and are considered to be the best that can be found (AWWA 1994, p. viii).

4 According to ASCE-NPFA, 2005, p , a broken 20-inch gas main under Balboa Boulevard was ignited by a driver of a nearby stalled pick-up truck who was attempting to start the vehicle. Ignition occurred about 20 minutes after the earthquake struck. Breaks in water mains rendered all surrounding fire hydrants inoperative. Fortunately, several homes in the area had swimming pools that were used as water supply sources. Northridge Earthquake and Gas Pipes (Lucas, 1994). The Southern California Gas Company (to be referred to as Company) operates a network of 87,000 miles of distribution piping and 3,300 miles of transmission piping. The Company discovered 209 minor and significant leaks directly attributed to the earthquake in the lower pressure, smaller diameter pipe distribution system. There were also 500 leaks that were classified as earthquake related. The vast majority of these leaks appear to have occurred in older steel pipes where minor corrosion conditions were accelerated by the seismic stress. Plastic (PE) pipe withstood the earthquake very well. There were 27 reports of plastic (PE) pipe system failures due to the earthquake About 41% of the gas piping in the affected area and in the SoCalGas system is plastic (PE). The transmission piping network is one of the largest systems in the US; high-pressure, large diameter pipes experienced 35 leaks. All leaks were repaired within 2 weeks. The majority of the leaks were in older (1930s) vintage welds. Several measures contributed to the excellent performance of the piping system... One of the measures is the use of plastic pipe. Since 1969, the Company has installed plastic (PE) pipe wherever possible. Today (i.e 1994) about 41% of our distribution system utilizes plastic (PE) pipe, which is less subject to earthquake damage. Also, the experience of the Company (SoCalGas) and PG&E in San Francisco is that PE is one of the best materials available because of its high ductility and ability to resist deflections from ground movement. Loma Prieta Earthquake and Gas Pipes (Philips and Virostek 1990). On October 17, 1989, the city experienced a large magnitude (7.1) earthquake with a PGA that exceeded 0.64g. The epicenter was about 60 miles south of San Francisco. Philips reported the following leaks as shown in Tables II, III, IV and V. According to the author, The leaks fell into three categories: Grade 1, Grade 2 and Grade 3. A Grade 1 leak represents an existing or probable hazard and requires immediate repair or action. A Grade 2 leak is not hazardous to life or property at the time of detection but requires scheduled repair. A Grade 3 leak is nonhazardous at the time of detection and is expected to remain so. Philips and Virostek (1990) also noted that the number of leaks that can be attributed to the earthquake is unknown and the documentation of the leak causes was not always clear or consistent. Per Tables II and III, PE failure ratio ranged between 0.01% and 0.1%; cast iron failure ratio was 2.8%; steel failure ratio ranged between 0.03% and 0.2%; copper had a failure ratio of 0.03%.

5 Table II: PG&E Grade 1 Leaks in Gas Distribution Mains Type of Pipe No of Leaks (Grade 1) Miles of Pipe (% of total) Failure Ratio (Leaks/mile) PE 9 9,436 (28.9%) 0.1% Cast Iron (2.4%) 2.8% Steel 56 22,428 (68.7%) 0.2% TOTAL 87 32,647 Table III. PG&E Grade 1 Leaks in Gas Services Type of Pipe No of Leaks (Grade 1) No of Services (% of total) Failure Ratio (Leaks/mile) PE ,107 (38.3%) 0.01% Copper ,273 (4.2%) 0.03% Steel 412 1,439,925(57.5%) 0.03% TOTAL 513 2,506,305 Table IV. PG&E Cause of Leaks (Grade 1+2+3) Damage by Outside forces External corrosion Other Dig- In Material failure Construction defects Frequency 56% 23% 12% 5% 3% 1% Table V. PG&E Location of the Highest Number of Leaks in Services and Distribution Mains Type of Material Leak Source Steel Cast Iron Copper PE Body of pipe 46 DM 202 SR 8 SR 6 DM 33 SR Valve 141 SR 12 SR Fitting 47 SR 18 SR Bell joint Note: DM= Distribution Mains SR = Services 19 DM The piping system included 5,324 miles of transmission pipes, 32,647 miles of distribution mains and 2,506,305 of gas services. According to the authors, PG&E s gas system performed very well given the magnitude of the earthquake. The transmission system was undamaged except for two cracked welds The leakage occurred in a 12-inch diameter section of 1930 gas-welded steel pipe operating at 350 psig. The leaks were repaired without interrupting service to customers. The distribution system sustained some damages from the quake. By far, the majority of damage occurred at locations of major ground disruption and where buildings moved off their foundations, severing gas lines. The cast-iron and steel systems were badly damaged. The plastic (PE) and remaining steel pipes performed well. Overall, PG&E repaired 1,094 leaks, and replaced over 60,000 feet of main and over 1,700 services. Great Hanshin Awaji (Kobe) Earthquake in Japan (Honda, 1998). Honda reported about the January 17, 1995 Kobe earthquake. The earthquake magnitude was 6.9 and

6 affected a region with a population of 2 million. Table VI lists the failure rates for different water and gas pipes. PE water and gas pipe had a failure rate (0.00) followed by DCIP (Ductile Cast Iron Pipe, for gas pipe) and Steel (0.437 for water pipe). According to the paper, Kobe city had about 1,600 water leaks from water distribution pipes. The leaks resulted from joints coming out (i.e. joint separation, 63%), broken pipe (20%), and other damages to the fixture (17%). Table VI: Kobe Earthquake Failure Rates of Water and Gas Pipes Type of Pipe PE Steel DCIP PVC CIP AC Water Pipe Damage/ km Gas Pipe Damage/ km Thailand Tsunami (ASCE 2005). The document reported about the prevalent use of HDPE piping for potable water. According to this report, much of this (PE) piping was exposed to erosion and subjected to harsh conditions from debris and waves. The (PE) piping performed very well with few failures. The material is flexible, allowing it to conform to new contours after the erosion. It is also very light, making repairs very easy. Columbia (Bresser, 2000, p. 7). The January 25, 1999 earthquake in Armenia, Columbia was a moderate earthquake and caused extraordinary damage. The chart below shows the failure rates among different water and gas pipelines. Note that PE, Ductile Iron and Reinforced Concrete had a failure rate of 0 per 10 km, followed by PVC (8), Asbestos Cement (9.5) and Cast Iron (9.7). Relative Vulnerability of Buried Pipelines (ASCE 2002). ASCE 2002 ranks the relative vulnerability of various materials to earthquakes as shown in Table VII: PE has a low vulnerability to earthquakes. Ductile Iron ranged between Low and Low Moderate; steel ranged between Low and High; Concrete Cylinder ranged between Low - Moderate, to High; PVC ranged between Low - Moderate, to Moderate; Cast Iron ranged from Moderate - High, to High; Vitrified Clay ranged from Moderate - High, to High and Asbestos Cement is High. A similar table (Ballantyne 2010) assigned numerical values (1 (worst) -5 (best)) to each pipe material, based on Ruggedness, Bending, Joint Flexibility and Restraint. Fused PE and arcwelded steel received 19 points and cast iron received 6 points; the points are shown in Table 7.

7 Table VII. Relative Vulnerability to Earthquakes of Buried Pipelines (ASCE 2002, p.44 and Ballantyne 2010) Material Type Low Vulnerability Low to Moderate Moderate Moderate to High High Polyethylene AWWA C906 (Fused joint)- 19 Ductile Iron C1xx series joint with rubber gasket, restrained)- 18 C1xx series joint with rubber gasket, unrestrained)- 15 Steel C2xx series (Arc welded joint or bell and spigot joint with rubber gasket, restrained)- 19 C2xx series joint with rubber gasket, unrestrained)- 15 No Designation (Gas welded joint)- 9 No designation (Riveted)- 18 Concrete cylinder C300, C303 joint, restrained)- 14 C300, C303 (Bell and spigot joint, unrestrained)- 12 PVC C900, C905 joint, restrained)- 13 C900, C905 joint, unrestrained)- 11 Cast Iron No Designation (Bell and spigot joint with rubber gasket) No Designation (Bell and spigot joint, leaded or mortared )- 6 Vitrified Clay No Designation (Bell and spigot joint with rubber gasket)-? No Designation (Rigid Jointed)-? Asbestos Cement C4xx (Coupled joint)- 9 Non-Earthquake Failures Beside the pipe failure data from past earthquakes, it is important to show and compare the failure data in regular non-seismic environments. As such, data from the Swedish water pipe network (Bresser 2000) and from the UK National Failure Database (MacKeller 2004) is

8 presented in the next 2 charts. Comparing both charts shows that PE has the lowest failure rates, followed by DI and PVC. CONCLUSION This paper summarized the performance of water and gas piping systems during six past earthquakes in four countries: US (1906 San Francisco; 1989 Loma Prieta; 1994 Northridge), Japan (1995 Great Hanshin-Awaji (Kobe), Thailand (2005 Tsunami), Columbia (1999). Most piping systems have not been designed and/or detailed properly to resist such hazards and most consulting firms are not required by their clients (owners) to address these hazards. This lack of requirements in seismically active or coastal zones may be due to lack of awareness about the effect of these hazards on pipelines, cost issues, performance, damage and priorities. Unlike standards for buildings and other structures, the AWWA pipe standards do not include specific requirements for the design, detailing and/or construction of pipes in seismic regions. Although AWWA and ASCE have published multiple reports on earthquake resistant pipeline design and performance, many pipe designers and utility owners may not be aware of these resources and the risk that is associated with the lack of design standards. In the absence of Standards, this paper summarized the risks and failures of different materials and provided data to assist the industry in protecting our underground pipe assets. All readers should refer to the actual publications for full review and implementation in their standards. In summary, the past earthquakes can teach us the following lessons: 1. Most, if not all, US states have experienced some earthquake as was listed in Table I. In summary, the state of Maryland (MD) experienced the lowest magnitude earthquake of 2.6 and the state of Alaska (AK) experienced the highest magnitude earthquake of 9.2. Due to the 3.6 July 16, 2010 earthquake in MD that has not been posted on the USGS website, the state of RI has now the lowest magnitude earthquake in the US, The magnitudes of the largest reported earthquake can be categorized as follows: Minor: : MD, RI Light: : LA, VT, GA, SD, WV, MI, MN, MS Moderate: : TN, AL, IN, KS, ME, NE, KY, NC, PA, IL, NJ, OH, OK, NH, ND, AZ, NY, TX and VA Strong: : CO, WY, UT, OR, WA, ID Major: : NV, MT, SC, CA, HI, MO, AR Great: 9.2: AK

9 2. The 1906 San Francisco earthquake destroyed the city downtown and fires burned for 3 days due to lack of water to control the fires. As such, the water system must be better designed to remain operational to minimize the effect of fire and destruction. 3. The 1994 Northridge earthquake resulted in damage to 3 water transmission pipes and over 1500 water system pipeline failures. It was noted that if this earthquake had occurred in other locations in North America, the water system would have been more heavily damaged than was seen in Northridge because the system was upgraded following the 1971 San Fernando Earthquake. 4. The 1994 Northridge earthquake resulted in 709 gas pipe leaks (lower pressure, smaller diameter pipes within the distribution and service system) and 35 high pressure, large diameter leaks in the transmission system. 5. After the 1989 Loma Prieta earthquake, it was not clear which leaks can be attributed to the earthquake; however, the researcher listed the leaks in gas mains and services. Per Tables II and III, PE failure ratio ranged between 0.01% and 0.1% (leaks/mile); cast iron failure ratio was 2.8%; steel failure ratio ranged between 0.03% and 0.2%; copper had a failure ratio of 0.03%. 6. The effects of the 1995 Kobe earthquake on water and gas pipes was discussed; per Table 6, PE water and gas pipe had a failure rate (0.00 damage/km); Ductile Cast Iron pipe (0.052 for gas pipe and for water pipe) and Steel pipe (1.210 for gas and for water). The remaining water pipe materials had the following damage rate: PVC (1.430), CIP (1.508) and AC (1.782). 7. The 2005 Thailand Tsunami reported about the prevalent use of HDPE for potable water and the piping system performed very well with few failures. 8. The 1999 Columbia earthquake reported the following failure rates: PE (0 failures/10 km), DI (0), RC (0), PVC (8), AC (9.5) and CI (9.7). 9. The ASCE 2002 tabulated the vulnerability to earthquakes of various pipe materials: PE has a low vulnerability to earthquakes. Ductile Iron ranged between Low and Low Moderate. Steel ranged between Low and High. Concrete Cylinder ranged between Low - Moderate, to High. PVC ranged between Low - Moderate, to Moderate. Cast Iron ranged from Moderate - High, to High. Vitrified Clay ranged from Moderate - High, to High. Asbestos Cement is High. In addition to the data that was presented on the performance of pipes in past earthquakes, the paper presented data from regular (non-seismic) applications in the UK and Sweden: The Swedish data showed the following failure rates: PE (0.3 failures/10 km), DI (0.4), PVC (1), CI (1.9) and Steel (3.3). The UK data showed the following failure rates: PE (3.2 failures/100 km), DI (5.3), PVC (7.3), Steel (11.1), AC (16), Iron (20.1) and Unknown (3.2). REFERENCES ASCE-NFPA (2005). Fire following earthquake, edited by C. Scawthorn, J. Eidinger and A. Schiff, USA

10 ASCE (1999). Guidelines for the seismic evaluation and upgrade of water transmission facilities, edited by J. Eidinger and E. Avila, American Society of Civil Engineers, Reston, VA. ASCE (2002). Seismic screening checklists for water and wastewater facilities, edited by W. F. Heubach, American Society of Civil Engineers, Reston, VA. ASCE (2005). Thailand team report: Tsunami disaster zone to conduct damage assessments, Feb. 3, Curtis Edwards, P.E., Vice President, Pountney Psomas Thailand Team Leader; ASCE/SEI 7-05 (2005). Minimum design loads for buildings and other structures, American Society of Civil Engineers, Reston, VA. AWWA (1994). Minimizing earthquake damage- A guide to utilities, prepared by D. B. Ballantyne, American Water Works Association, Denver, CO. Ballantyne, D. (2010). Seismic vulnerability assessment and design of pipelines. AWWA Journal, May 2010, pp Bresser, R., Tauber, M. (2000). Global success stories for PE pipe systems in water transportation and distribution; Cornell University (2006). Cornell earthquake lab conducts largest test ever of how shifting earth might impact buried pipes, Honda, Hisachika (1998). The evolution and present state of polyethylene (PE) water pipes in Japan, Proceedings of the 10 th Plastics Pipe Conference, PP X, Goteborg, Sweden. IBC-06 (2006). International Building Code, International Code Council, Falls Church, VA. Lucas, Jerry (1994); Southern California gas company response to the Northridge earthquake, Proceedings of the National Conference of Regulatory Utility Commission Engineers, June 12-17, St. Louis, Missouri. MacKellar, Steve (2004). Operation of plastic pipe systems, presented at Plastics Pipes XII, Baveno, Italy. NRC (2003). Preventing Earthquake Disasters, National Research Council of the National Academies, Washington, DC. Philips, Steven and Virostek, Kris (1990). Natural gas disaster planning and recovery: The Loma Prieta earthquake; Operating Section Proceedings, American Gas Association, p Van Dyke, Steve (1997). San Francisco fire department water supply system, San Francisco Fire Department, CA