Feb. 14, 2011 - Boulder, Colorado
AWWA Document Revision Provides Specification Requirements of Large Diameter Water Pipes & Materials
Authored by Steve Ferry, Managing Director, Microbac Laboratories, Inc., Hauser Division
The American Water Works Association (AWWA), recognized as a standards organization that advances public health, safety and welfare by focusing on safe water policy issues, has released a significant revision to the AWWA standards document ANSI/AWWA C905, “Polyvinyl Chloride (PVC) Pressure Pipe and Fabricated Fittings, 14 In. Through 48 In. (350 mm Through 1,200 mm)”. This new revision document C905-10 provides for product specification requirements of large diameter water transmission pipe products and materials.
The AWWA C905-97 standards document has experienced significant changes between the 1997 edition and the newly-approved 2010 edition (ANSI/AWWA C905-10). While the requirements for the Hydrostatic Integrity Test have remained the same, major changes are noted in the revision, including the expansion of surge pressure design information to include occasional (emergency) and recurring (cyclic) surges. While not listed as major revisions, the addition of Sustained Pressure and Burst Pressure tests as updates to the Pipe Requirements Section are also noteworthy. The additions of the Sustained and Burst Pressure tests and requirements to the Pipe Requirements Section were made, reportedly, in anticipation that the AWWA standards C900 and C905 would eventually merge. ANSI/AWWA C900-07, AWWA Standard for “Polyvinyl Chloride (PVC) Pressure Pipe and Fabricated Fittings, 4 In. Through 12 In. (100 mm Through 300 mm), for Water Transmission and Distribution” currently has the Sustained Pressure and Burst Pressure test requirements contained therein, although there are some minor differences between the two documents.
Applying these tests to larger diameter pipe products will generate major obstacles for commercial testing laboratories since most laboratories are generally not equipped to handle pipe and ancillary equipment such as test caps in these (newly-required) larger diameters. Partly due to the size, but more importantly due to the weight of the sample and test caps and also the complexity of fixturing required to contain the forces generated upon pressurization, commercial laboratories will be required to substantially evaluate the facilities, equipment, and safety requirements to support this new line of testing.
The Sustained Pressure test within AWWA C905 Section 18.104.22.168 requires the testing of a single sample in general accordance with ASTM D1598 (Standard Test Method for Time-to-Failure of Plastic Pipe Under Constant Internal Pressure), which is similar to the testing requirements contained within AWWA C900, and as modified within ASTM D2241 (Standard Specification for Poly(Vinyl Chloride) (PVC) Pressure-Rated Pipe (SDR Series)). The AWWA C900-07 standard currently requires testing of six (6) individual test samples, while the AWWA C905-10 requires only one sample to be tested. This is a key point for testing laboratories: Although the cost of the caps required for small pipe testing (up to approximately 4-inch nominal diameter) are not inconsequential, the costs for large diameter test caps are significant.
If one takes as an example a sustained pressure test performed on a 30-inch nominal diameter DR25 sample, the required test pressure would be 350 psi. The pipe sample itself will weigh hundreds of pounds. The test pressure is generally above the rated pressure of commercially-available pipe appurtenances such as a MJ-type cap. The weight of one of the caps alone is approximately 600 pounds. The resulting weight of sample plus caps would be approximately 1500 pounds, and this does not include the weight of any end-thrust reinforcement or fixturing or the weight of the water interior to the sample. The required test pressure would generate approximately 280,000 pounds of force (end thrust) on the test caps, which must be restrained. As compared to typical designs for smaller pipe tests where cages, allthread, bulkheads, etc., are used to facilitate the testing, the larger pipe would require a significant engineering scale up to accommodate the larger diameters and forces. Finally, the energy stored in a pressurized sample of this volume is much larger than typically encountered in the testing of small to medium diameter pipe, and additional safety equipment and systems would be necessary.
The Burst Pressure requirement within AWWA C905 Section 22.214.171.124 specifies five (5) test samples, two (2) of which require the integral bell to be in place, thus necessitating the testing of a spigot and or a male cap as opposed to the typical female MJ-type cap noted above. Additionally, the same engineering issues come into play as those encountered in the sustained pressure test, complicated yet again by the higher stresses and test pressures involved in this line of testing. It is also anticipated that there will be substantial lead times related to the fabrication of high pressure test caps and restraining fixtures as a result of the complex machining and welding required. As an alternative, however, Section 5: Verification of the AWWA C905-10 document does allow for testing of samples by the ring-tensile test of ASTM D2290 (Standard Test Method for Apparent Hoop Tensile Strength of Plastic or Reinforced Plastic Pipe by Split Disk Method), with comparison to the (embedded) wall stress burst requirement. It should also be noted that testing of large diameter hoop samples for ring tensile is also a complicated endeavor for a testing laboratory, again, due to the large forces and weights involved with the larger pipe.
Overall, the addition of these two hydrostatic pressure test requirements to the newly-approved edition of AWWA C905-10 represents a major step forward for engineers and system owners in evaluating the pressure-carrying capabilities of this product line. Additionally, commercial testing laboratories will have another set of tests with which to evaluate product that may not be performing to expectations in the field or during a failure analysis investigation. Commercial laboratories will, however, need to facilitate a new level of test engineering and safety demands.
Microbac Laboratories, Inc., Hauser Division in Boulder, Colorado has significant experience in the field of pipe testing to meet the specifications associated with AWWA C900-97, C905-97 and C905-10.
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