 |
Materials Testing |
Tel: (918) 258-6066 |
Report No : 2003100233 Date Received : 10/10/2003 Date Reported : 11/06/2003
Subject: Evaluation of Fusion of 12 Inch Diameter Polyethylene Pipe
Dear Mr. McKinley:
We have completed the evaluation of the 12 inch diameter polyethylene pipe fused together on the 14th and 15th of October, 2003. Nine samples of polyethylene pipe were fused using various parameters using a McElroy machine. The fusion process is shown in Figure No. 1. The inside and outside bead temperatures were monitored while the time the load pressing the fused edges was varied. The application of cooling air to the outside of the pipe was one of the parameters varied. Tensile loads were applied to the fused joints while the pipe was still in the McElroy machine. Bend specimens were removed and tested from the pipe, as shown in Figure No. 2 and Figure No. 3. The specimen did not fail when they were place under a bending load. Tensile specimens were removed from seven pipe joints and tested per ASTM D638 using a Lloyd tensile machine, as shown in Figure No. 4. The test specimens exhibited a relative narrow range of tensile strengths of 3,359 psi to 3,526 psi. The tensile specimens exhibited a large range of elongation from 91% to 500%, as shown in Figure No. 5. The tensile specimens exhibited a range of modulus of 140,900 psi to 334,800 psi.
Material
The pipe tested was black polythene 12 inch diameter identified as SR11. The pipe was fused and pull tested under the conditions shown in Table No. 1.
Data
Temperature Testing is the cooling curves of the outside and inside beads measured during the fusing of the pipe for tests 2 through 8. Pull Testing is the curves showing the applied load to the joints of pipe immediate after it was fused. Tensile Testing is the numeric results and load vs. displacement curves of the tensile tests conducted.
Discussion
The outside bead, as expected, responded to the presence of cooling air, as shown in the graphs for samples 5, 6, 7 and 8. There was no clear cut relation between the temperature of the inside bead and the presence of cooling air on the outside of the pipe.
None of the pipe joints failed when a load was applied to the pipe soon after the fusion process was completed. Based on the cross sectional area of the pipe, a 7,000+ lbs applied load translates into an applied stress of approximately 200 psi. The tensile strength of the samples removed from all of the pipe samples exhibited a narrow range of values. This indicated that the different conditions used to fuse the pipe did not affect the final tensile strength. All, except one, of the tensile specimens failed at the edge of the fused area. None failed through the fused joint. All the elongation took place the pipe material. This means that the fused joint is stronger than the polyethylene used to make the pipe. Low and medium density polyethylene should exhibit a tensile strength between 1200 and 4550 psi, while high density polyethylene should exhibit a tensile strength between 3200 and 4550 psi. The tensile strengths measured fall within the expected range. The modulus is given, but does not play a role in the soundness of the fused joint. The modulus of a plastic material becomes important when it is used to support a bending load.
Conclusion
The time pressure was held after the heated ends of the pipe were brought together was varied from 210 seconds to 105 second. These times represent a 50% and 75% reduction in the normally held time of 420 seconds. Within the range of parameters the pipe joints were produced, there was no significant difference in the tensile strength of the fused joint. In all cases it was greater than the polyethylene use to produce the pipe. The elongation varied from 91% to 500% with individual joints exhibiting variations as great as 400% between the low and high values. Per 49CRF, 192.283 (a)(iii)(3) “Plastic pipe: qualifying joining procedures” states that specimens elongating no less than 25% or failure initiates outside the joint area qualifies the procedure used. The specimen tested qualify under 49CRF, 192.283 (a)(iii)(3).
Sincerely,
W. Don Bunn, PE
Project Engineer