PVC Failures. Russ Dueck, P.Eng. City of Calgary, Water Resources UDI Breakfast Seminar September 8, 2010

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1 PVC Failures Russ Dueck, P.Eng. City of Calgary, Water Resources UDI Breakfast Seminar September 8, 2010

2 PVC Watermain Reliability Distribution System is 50% PVC PVC breaks account for 1-3% of total annual break count PVC failures are typically catastrophic, leading to substantial water loss and sinkholes.

3 PVC Watermain Reliability PVC Failures Last 30 Years 157 Failures Failures on All Pipe Materials Within 30 Years of Installation 10,495 Failures

4 PVC Watermain Reliability

5 Recent Failures Northwest Calgary December 2008 Repair Cost = $82,000 Southeast Calgary July 2009 Repair Cost = $57,800 Southwest Calgary September 2009 Repair Cost = $182,500 Average repair cost of watermain breaks in 2009 = $14,000

6 Northwest Failure December 2008 Installation Year: 2001 Size: 250 mm Class: DR-18 Failure Mode: Split initiating at bell Probable Causes: - Longitudinal bending combined with joint deflection. - Joint deflection above maximum accepted deflection of three degrees. - Over-insertion of spigot into bell - Soil movement (bedding conditions)

7 Northwest Failure December 2008 Note depth of insertion of spigot in bell

8 Northwest Failure December 2008 Note deflection

9 Northwest Failure December 2008 Note spigot impressions on bell

10 Southeast Failure July 2009 Installation Year: 1981 Size: 300 mm Failure Mode: Split Probable Causes: - No clearance between 1800 mm storm duct and PVC pipe, thus causing longitudinal bending. 300 mm vertical separation is required at crossings. - Soil settlement

11 Southeast Failure July 2009 Note lack of vertical separation

12 Southeast Failure July 2009

13 Southwest Failure September 2009 Installation Year: 2004 Size: 250 mm Class: DR-18 Failure Mode: Split initiating at bell Probable Causes: - Longitudinal bending either due to improper installation or insufficient bedding - Joint deflection above maximum accepted deflection of three degrees - Over-insertion of spigot into bell

14 Southwest Failure September 2009 Note road sub-grade damage

15 Southwest Failure September 2009 Note how the pipe as sprung after being cut

16 Southwest Failure September 2009 Note longitudinal deflection

17 Southwest Failure September 2009 Note depth of spigot in bell

18 Southwest Failure September 2009 Note spigot impressions (partially highlighted in black)

19 Root Cause Analysis The causes of the failures were one or a combination of the following: Over insertion of the joint. Joint deflection above maximum accepted deflection guidelines. Pipe stress due to longitudinal bending. Lack of vertical separation from an existing utility.

20 Root Cause Analysis Over insertion of the joint: Uni-Bell Recommendations: A gap should exist between the inside of bell and spigot. Spigot should not bottom in bell. Over-inserted pipe will cause point load and bell distortion.

21 Root Cause Analysis Joint deflection above maximum accepted deflection guidelines: Manufacturer s Installation Guide (In accordance with Uni-Bell, AWWA C-900, and AWWA M23) Joint deflection and longitudinal bending shall not be combined on the same pipe. Joint deflection requires assembly ½ less than insertion line Maximum joint deflection for 250 mm pipe = 3 degrees

22 Root Cause Analysis Pipe stress due to longitudinal bending: Manufacturer s Installation Guide (In accordance with Uni-Bell, AWWA C-900, and AWWA M23) Joint deflection and longitudinal bending shall not be combined on the same pipe. Longitudinal deflection of 250 mm DR-18 pipe and larger is not recommended.

23 Root Cause Analysis Lack of vertical separation from an existing utility City of Calgary Standard Specifications for Waterworks Construction Sec (2009) requires a vertical separation of 300 mm between water, sanitary and storm main crossings. The same 300 mm requirement existed in 1981, as it was implemented after PVC was approved as a water pipe material. Prior to PVC approval, 150 mm was the distance required when ductile iron was the primary material used.

24 Summary In all three cases, aspects of the installations did not conform to the relevant City of Calgary Waterworks Specifications, Uni-Bell recommendations or Manufacturer guidelines. It is apparent that the failures resulted from design or construction errors that were never rectified. Although the piping designs did not appear to be the primary cause of failure, designers should be cognisant of the complications that tight tolerances create in field conditions. For example, Consultants need to ensure that where pipe designs include curved alignments or cross other utilities, that it is noted on the drawings that the installation of deflection bends may be required. As well, simple details such as pipe wall thickness need to be taken into consideration in designs. By identifying potential conflicts and limitations at the design stage, Contractor s will be better prepared to install the pipe within specifications. Contractors and Consultants need to ensure that workers are educated on Standard Construction Specifications and install pipe according to the manufacturers guidelines. This includes educating workers on the potential consequences of improperly installed PVC pipe, such as catastrophic pipe failures and sinkholes. Manufacturers should ensure that installation guidelines state a maximum insertion distance, and that factory insertion lines are marked for all sizes and classes of pipe. Manufacturers play an important role in continually educating designers and installers on the proper methods of PVC pipe installation.