1、 Erosion Study on Brass Insert Fittings Used in PEX Piping Systems TN-26/2013 Foreword This report was developed and published with the technical help and financial support of the members of the Plastics Pipe Institute (PPI). These members are committed to developing and improving quality products b
2、y assisting independent standards and user organizations in the development of standards, and also by developing design aids and reports to help engineers, code officials, specifying groups, contractors and users. The purpose of this technical note is to provide information on a test program to eval
3、uate the effects of flowing water on copper alloy fittings insert fittings used in crosslinked polyethylene (PEX) hot and cold water distribution tubing systems, and to provide information to aid in the design of PEX plumbing systems sized using model plumbing codes. The PPI has prepared this techni
4、cal note as a service to the industry. The information in this report is offered in good faith and believed to be accurate at the time of its preparation, but is offered “as is” without any express or implied warranty, including WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. Add
5、itional information may be needed in some areas, especially with regard to unusual or special applications. Consult the manufacturer or material supplier for more detailed information. A list of member manufacturers is available on the PPI website. PPI does not endorse the proprietary products or pr
6、ocesses of any manufacturer and assumes no responsibility for compliance with applicable laws and regulations. PPI intends to revise this report within 5 years or sooner if required, from the date of its publication, in response to comments and suggestions from users of the report. Please send sugge
7、stions of improvements to the address below. Information on other publications can be obtained by contacting PPI directly or visiting the web site. The Plastics Pipe Institute Inc. www.plasticpipe.org This Technical Note, TN-26/2013, was first issued in October 2005 and was revised in December 2013.
8、 2 PPI TN26/2013 EROSION STUDY ON BRASS INSERT FITTINGS USED IN PEX PIPING SYSTEMS Background: Most PEX plumbing systems are installed using some form of insert fitting. These fittings are usually made from brass or some other copper alloy. Because the insert portion of the fitting has a smaller dia
9、meter than the tube, the velocity of the water through the fitting is higher than the velocity of the water in the tube. PEX systems, delivering the same volume of water will have higher flow velocities in the tube and fittings than copper systems of the same nominal size. Many plumbing codes have m
10、aximum recommended flow velocities for copper or copper alloys in plumbing systems to prevent erosion of the system from the flowing water. Millions of brass insert fittings have been installed in PEX plumbing and heating systems over the past 20 or more years in Europe and the United States. In tha
11、t time, we are unaware of any erosion induced failures of PEX piping systems In order to more fully evaluate this subject, the Building Construction Divisionof the Plastics Pipe Institute funded a test program at Materials Performance Inc. in College Station, TX. Objective: The objective of this tes
12、t program was to subject different brass insert fittings for PEX plumbing systems to flow rates that represented the maximums that could occur if a plumbing system was sized according to the 2000 version of the Uniform Plumbing Code and then flowing enough hot, chlorinated water through them to be e
13、quivalent to 40 years of service in typical single family residence. Results: None of the brass insert fittings for PEX systems failed during this test. Weight losses were less than 3% for all fittings. Internal diameter increases due to erosion were less than 1%. ” copper sweat elbows with straight
14、 pieces of copper tube attached were subjected to the same condition as the ” brass insert fittings for PEX and these did not fail either. Conclusions: The results indicate that very little erosion occurs at the test conditions chosen. The water conditions chosen were at the severe end of normal pot
15、able water conditions and the water flow rates were the maximum that should be experienced when all fixtures on a given line are open and flowing at capacity. No failures occurred and based on these results, failures due to internal erosion of brass insert fittings in PEX plumbing systems would not
16、be expected over a normal lifetime of a plumbing system. PEX piping systems with brass insert fittings can be sized following the tables published in the model codes without undue concern for erosion of the fittings in normal plumbing applications. 3 Discussion: The test program given to the lab is
17、listed in Appendix A. It is considered to be aggressive relative to most plumbing installations for the following reasons. 1. The water temperature was maintained at 140F for the duration of the test. In a normal residential plumbing system, some flows occur at lower temperatures on the hot water si
18、de of the system because the water-cooled off when the line was not in use. 2. In the test, the total volume water was flowing at the elevated temperature. In a normal residential system, the total flow for the structure is divided between the hot and cold sides of the system. The only fittings that
19、 actually have the total volume of the water being used by a residence passing through them are the fittings on the cold-water inlet line before flow splits at the water heater. 3. The pH of the water was maintained between 6.5 and 6.7. This is corrosive and much lower than the 6.9 to 7.1 range that
20、 is common for water systems. 4. The water velocity for the entire life of the test was at a velocity that assumed all fixtures on a line would be open to their maximum at the same time. In normal systems, usually only a small percentage of the maximum possible flow is experienced at one time so mos
21、t of the water flows at velocities that are much lower than the possible maximum. 5. The chlorine level of the water was maintained between 2.5 and 3.0 ppm for the duration of the test. The average chlorine level for water systems in the U.S. is about 1.0 ppm. It would be an unusual circumstance for
22、 a residence to experience chlorine levels equal to the test condition for an extended period of time. Three different fitting types were tested. A. Fittings machined from brass rod, Alloy C36000, to ASTM F1807 B. Fittings machined from forged brass, Alloy C37700, to ASTM F1807 C. Fittings machined
23、from forged brass, Alloy C37700, to ASTM F1960 The total water flow through each size fitting during the test is listed below. Size Water Flow 3/8” 700,125 gallons ” 1,400,250 gallons ” 4,200,750 gallons The water velocities for each type of fitting are listed below. Size ASTM F1807 ASTM F1960 3/8 1
24、9.3 ft/sec 13.8 ft/sec ” 16.7 ft/sec 13.4 ft/sec ” 21.8 ft/sec 16.7 ft/sec 4 The results are tabulated and illustrated in the following tables and graphs. Table 1 Weight loss of ” fittings at end of test. Table 2 Weight loss versus gallons of flow through ” elbows. Table 3 Weight loss of ” fittings
25、at end of test. Table 4 Weight loss of 3/8” fittings at end of test. Because the ” fittings had the highest flow velocities, the ” elbows were selected to be checked for weight change at 1,000,000 gallon intervals during the test. As would be expected, the weight loss did trend up as the amount of w
26、ater flowing through the fittings increased. Table 4 does not have any 3/8” fitting data from F1960 type fittings because they were not available at the time of the test. The fittings of each type with the largest weight loss were sectioned and examined for signs of pitting. There were no signs of l
27、ocalized pitting that would indicate a probability of early fitting perforation due to localized material loss. Because of the very aggressive conditions during the test, a section of ” PEX tube was also evaluated for any dimensional changes at the end of the test. There was no measurable change in
28、the PEX tube. Based on these results, it seems unlikely that PEX plumbing systems using brass insert fittings, sized according to the tables in the Uniform Plumbing Code for copper tubing, will fail from erosion of the fittings caused by high water velocities in normal residential applications. 5 %
29、Weight Loss vs Fitting Type 3/4“ 4200750 Gallons - Table 100.511.522.5Fitting type%WeightChange (Decrease)F1807 C360 3/4F1807 C377 3/4F1960 C377 3/4F1807 C360 3/41.19 1.32 2.09 1.36F1807 C377 3/42.18 0.89 1.47 0.87F1960 C377 3/40.86 1.09 0.98 0.92Elbow Tee1 Tee2 Coupling6 % Weight Loss vs Gallons Th
30、rough 3/4“ Elbows - Table 200.511.522.5Gallons of Water%WeightChange (Decrease)F1807 C360 3/4F1807 C377 3/4F1960 C377 3/4F1807 C360 3/41.07 1.21 1.81 1.19F1807 C377 3/40.48 0.92 1.97 2.18F1960 C377 3/40.48 0.55 0.75 0.861E+06 2E+06 3E+06 4E+067 % Weight Loss vs Fitting Type 1/2“ 1400250 Gallons - Ta
31、ble 300.20.40.60.811.21.41.61.8Fitting Type%WeightChange (Decrease)F1807 C360 1/2F1807 C377 1/2F1960 C377 1/2F1807 C360 1/2 0.75 1.29 1.65 1.68F1807 C377 1/2 1.28 1.61 1.27 1.63F1960 C377 1/2 0.95 0.91 0.89 1.04Elbow Tee1 Tee2 Coupling8 % Weight Loss vs Fitting Type 3/8“ Fittings 700125 Gallons - Ta
32、ble 400.20.40.60.811.21.41.61.82Fitting Type%WeightChange (Decrease)F1807 C360 3/8F1807 C377 3/8F1807 C360 3/80.85 0.98 1.77 1.2 1.67F1807 C377 3/80.93 0.64 1 1.71 1.86Elbow1 Elbow2 Tee1 Tee2 Coupling9 Appendix 1 TN-26/2013 10 Plastics Pipe Institute HTD Project 97-03 Revision 1 10-8-99 Flow Erosion
33、 Test For PEX Fittings Objective: The objective of this test procedure is to see if the water flow that might be experienced in a typical, non-recirculating plumbing system will cause failure of the metal fittings that are used in PEX plumbing systems in a reasonable lifetime. We will also check to
34、see if there is any erosion evident in the PEX tube during this test. Test Description: A system will be set up with fittings of all sizes and common geometries. Hot water will be circulated through the fittings at flow rates that result from sizing a plumbing system according to the Uniform Plumbin
35、g Code. The amount of water circulated will be equivalent to the average household usage for 40 years based on most recent usage information from AWWA and household population information from the U.S. Census Bureau. After testing, the fittings will be examined for signs of erosion and weighed to de
36、termine the percentage weight loss. Water Temperature: The circulating water temperature will be 140F at the inlet to the system. The exit temperature for any loop will not be below 135F. Water Quality: The pH of the water will be maintained between 6.5 and 6.7. The chlorine level will be maintained
37、 between 2.5 and 3 ppm. These values may be converted to ORP values for control purposes. The water shall be “Moderately Hard” as determined by one of the following measures. The hardness shall be between 3.6 and 7 grains per gallon, or the CaCO3 shall be between 75 and 150 mg/l. The water shall be
38、filtered using a potable water sediment filter. The filter shall have a nominal rating of 50 microns. To minimize the possibility of unexpected changes in water quality due to mineral or other chemical build ups, 5 gallons per hour of the circulating water should be replaced with make-up water. 11 W
39、ater Flow Rates: The water flow rates are taken from Table 6-4 in the Uniform Plumbing Code that gives the capacity of tubes of various lengths in Fixture Units. The maximum value shown for a size is the value that is used. 3/8” is not covered in this table. For 3/8”, we used the maximum Fixture Uni
40、t device that is shown to be acceptable for connection to a 3/8” tube which is 3 for a flush tank toilet in Table A-2. All values for fixture units are for private use. The Fixture Unit values were then converted to gpm by using Chart A-3. Tube Size WSFU gpm 3/8 3 2.5 7 5 20 15 Water Volume: The vol
41、ume of water to be passed through the fittings must be enough to simulate 40 years of service. The WaterWiser web page of the AWWA , updated in 1999, gives the average daily use per person as 72.5 gallons. The U.S. Census Bureau shows that the average household has slightly less than 3 people in it.
42、 To be conservative, we will assume a household with 4 people. This gives a total volume of 4,234,000 gallons used in 40 years. This will be the amount of water that must be passed through the ” fittings. With a flow rate of 15 gpm, 24 hours a day, 7days a week, it will take 28 weeks for 4,234,000 g
43、allons of water to pass through ” fittings. Using this length of time, the following amount of water will be passed through the 3/8” and ” fittings at their target flow rates. 3/8” 705,600 gallons ” 1,411,200 gallons Water Velocities: Using the minimum IDs published in the fitting standards, the fol
44、lowing water velocities (ft/sec) will occur in the fittings at the flow rates required by this test. Size F1807-Brass F1807-Copper F1960-Brass 3/8 19.3 19.3 13.8 16.7 16.7 13.4 21.8 21.8 16.7 12 Data To Be Taken At Start Of Test: For each fitting tested, the following information will be recorded. 1
45、. The ID of each insert portion of the fitting in thousandths of an inch. 2. The weight of each fitting to the hundredths of a gram. 3. Note if there is a smaller ID other than the insert portion of the fitting. Other information to be recorded for each system. 1.The weight of the copper assembly 2.
46、 Wall thickness in 4 places on each end of a piece of ” tube. Make a 3 inch long mark along the tube length at the location of each measurement. This tube will be cut out at the end of the test and the wall thickness will be checked at these marks. Installation Requirements: Each fitting shall be in
47、stalled in PEX tube according to the manufacturers instructions. The distance between any fitting and the next one must be at least 30 tube diameters except for the two 3/8” elbows. These two fittings should only have a distance of 2” between the insert portion of the fittings. If the PEX tubing is
48、bent or curved, no fitting shall be closer than 30 tube diameters downstream of the bend. The direction of flow through each fitting shall be marked on the fitting. A schematic of a typical set-up for a fitting system is shown in Figure 1. Other arrangements could be used. Fittings To Be Tested: At
49、a minimum, two tees, an elbow and a coupling of each size, from each material from each standard shall be tested. One of the tees will be tested with flow in the straight through direction and the other will be tested with flow coming in the straight through direction and out the branch. For the ” size, 3 additional elbows will be installed in the system. One of these will be removed after 1 million gallons of water flow and the others will be removed at 2 and 3 million gallons of water flow. If other fittings are required for plumbing the system and th
