Moser A.P., Folkman S. Buried Pipe Design

Подождите немного. Документ загружается.

TABLE 7.13 Summary of Reported Long-Term Problems with PVC Pipe

Is rate Pipe Testing

Utility no./ No. in last Average time increasing AWWA Pipe manu- samples

problem type 5 years in service, yr or decreasing? or ASTM size, in facturer available Details

Utility 19

Joint 5 15–20 Static AWWA 6 ? No No correlation between

problem and pipe proximity

to pumps and valves

Bedding 2–3 per year 15–20 Decreasing AWWA 6 ? No Problem with poor bedding

not pipe’s fault

Utility 26

Joint Not sure 5–8 Decreasing ASTM CL 160 2 ? No Problems w/glue joints,

not rubber ring, usually class

160 pipe; don’t use glue joints

anymore

Utility 48

Joint 4 10 Static AWWA 6, 8 ? No Not near any pumps or valves;

pipe deflected around inlet box

Utility 51

Pressure 10–15 10 Decreasing ASTM 2 A No Pipe in proximity of pump

station; pressure 190–250 lb/in

;

pipe is class 200

Bedding 2 10 Decreasing ASTM 2 A No Problem with digging down

and hitting pipe; is brittle

and breaks; soil has pH of

6.5, class 200

Utility 103

Pressure 10 5 Decreasing AWWA 80%, 6 ? Yes Bad soil conditions;

20%, 8 pipe had defect

Joint 20 1–5 Decreasing AWWA 80%, 6 ? Yes Problem occurs when joint

20%, 8 is made between PVC and

some other type of pipe

449

450

TABLE 7.13 Summary of Reported Long-Term Problems with PVC Pipe (

Continued

)

Is rate Pipe Testing

Utility no./ No. in last Average time increasing AWWA Pipe manu- samples

problem type 5 years in service, yr or decreasing? or ASTM size, in facturer available Details

Utility 151

Pressure 65 5–6 Decreasing ? 10 ? Pipe laid on Coquinia rock

(coral-like) when combined

with water hammer

rubbed weak spot

Utility 156

Pressure 5 8 Static ASTM 6, 8 ? Call Problem with ASTM class 200,

not C900; thinks due to old-

age brittleness

Utility 163

Pressure 5–8 10–30 Decreasing ASTM C 1160 6, 8 B No Believes problem due to

manufacturer and class

160 pipe

Joint 8 10–30 Decreasing ? 8 ? No Problems with slip joint;

not sure of cause; came and

went in 1 year (probably

personnel)

Utility 166

Pressure 250–300 6–18 Decreasing ASTM C 1200 6, 8 A Yes Could be due to changes in

pressure; varies from

20–200 lb/in

Joint 100 6–18 Decreasing ASTM C 1200 6, 8 ? Yes Problem occurs around bell

and spigot; lots of surges,

system unstable

Plastic Flexible Pipe Products 451

Percent of Total

<1 1–5 5–10 >10

Time Period (

ears)

Only AWWA Users

Only Those Who

Answered Yes

Figure 7.37 When PVC pipe problems occurred—a comparison of those who have expe-

rienced problems due to exposure to ultraviolet light with AWWA C900/C905 PVC pipe

users.

Percent of Total

<1 1–5 5–10 >10

Time Period (years)

Only AWWA Users

Only Those Who

Answered Yes

Figure 7.38 When PVC problems occurred—a comparison of those who reported using

sunburned pipe with AWWA C900/C905 PVC pipe users.

452 Chapter Seven

Percent of Total

<1 1–5 5–10 >10

Time Period (years)

Only AWWA Users

Only Those Who

Answered Yes

Figure 7.39 Comparison of when pipe problems occurred for AWWA C900/C905 PVC

pipe users with those who reported problems with aggressive chemicals.

Percent of Total

<1 1–5 5–10 >10

Time Period (years)

Only AWWA Users

Only Those Who

Answered Yes

Figure 7.40 Comparison of when pipe problems occurred for AWWA C900/C905 PVC

pipe users with those who reported problems with a particular manufacturer.

Plastic Flexible Pipe Products 453

and the age of the pipe, with one exception—the group who answered

yes to the question “Do you use sunburned pipe?” has more problems

with pipe older than 10 years. However, the data may not be statisti-

cally valid since each subgroup is small. Also, there is no direct link

with a particular problem in a specific length of pipe and the age of that

length of pipe.

Water hammer. Data from a question concerning water hammer prob-

lems were linked with data from the question concerning system pres-

sure variations. Results are given in Fig. 7.41.

Testing of pipe samples supplied by utilities. The extent to which a field

sample is useful depends to a large degree upon the documentation

provided by the utility supplying the sample. Efforts were made to

identify the manufacturer, date of manufacture, and the likes, on each

pipe sample. In some cases, this information could not be determined.

Each of the utilities involved in the follow-up phone survey was

asked if it could provide PVC pipe samples for testing. The intention

was to obtain as many pipe samples as possible from those utilities

reporting long-term problems and those utilities having numerous cata-

strophic tapping failures. These pipe samples were to be taken from pipes

where actual problems had been experienced. Extreme difficulty was

experienced in obtaining samples of actual pipe that had experienced

100

Percent of Total

<20 20–40 >40

No Problem

Problem

No Response

Water Pressure Fluctuation (lb/in

)

Figure 7.41 A comparison of water pressure fluctuation and whether the respondents

consider problems due to water hammer and/or transient pressure to be either a prob-

lem or not a problem.

454 Chapter Seven

problems. For the most part, the utilities indicated that such pipe sam-

ples were no longer available, but they would call us if new problems

occurred. A genuine reluctance on the part of most utilities to con-

tribute pipe samples for testing was sensed. The reasons for this resis-

tance are unknown, but one reason may be they were not sure of

anonymity. Another possibility is that they were concerned with what

the results may show. However, two utilities supplied pipe samples for

testing. Results of these tests are included in this book.

Selected utilities who had reported problems were then asked to

supply samples of PVC pipe they were currently installing. These sam-

ples were representative of PVC pipe that was currently being deliv-

ered to the utilities and of PVC pipe that was being manufactured.

Sixteen utilities from throughout the United States responded with

samples. The samples included pipe from 10 separate manufacturers.

Test methods. The pipe samples were subjected to the following three

tests to determine basic composition and extrusion quality.

1. A degree of fusion test: The procedures and limitations prescribed

in ASTM D 2152 were followed.

2. An impact test: This test procedure is as prescribed in ASTM D

2444 along with the standards described in ASTM D 2241.

3. Filler content test(s): The filler content was determined by one or

both of the following test methods. (Cell class information is given

in ASTM D 1784.)

a. A burnout test which consists of weighing a sample of pipe,

approximately 1 in square, burning the sample for a sufficient

length of time to burn off the resin, and then weighing the

residue to obtain the amount of filler.

b. Specific gravity (density) was determined by weighing samples

in air and then determining volume by displacement of a liquid.

Tests on samples of problem pipe. As stated above, only two utilities sup-

plied pipe samples from “problem pipe.” All pipe from utility 70 was

manufactured and installed in the 1970 to 1972 time frame and was

from a single manufacturer. This utility is one of the largest users of

PVC pipe in the United States, with several hundred miles of PVC pipe

installed. The utility manager was certain that this was inferior pipe

because of continued problems with it over the years. The failure rate

was decreasing with time, but simply because the problem pipe was

gradually being replaced.

The second utility (utility 166) to supply problem pipe samples indi-

cated some problems, but did not have as long a history for the partic-

ular pipe samples in question. The samples provided were also from a

single manufacturer, but no date markings were evident on the sam-

ples so the date of manufacture is not known.

Plastic Flexible Pipe Products 455

Table 7.14 summarizes the results of tests performed on pipe samples

from these two utilities. The filler content is provided as percent by

weight and by parts by weight. The parts-of-filler listing is based on 100

parts of PVC resin. As can be seen, samples provided by utility 70 are of

questionable quality. The 2-in and 3-in pipe samples have too much filler,

and the 4-in, 6-in, and 8-in samples are of poor fusion quality. It appears

that these pipes may have been extruded on a twin-screw machine with

low heat on one side of the extruder. Samples from utility 166 that passed

the acetone test have little or no filler content and generally appear to be

okay.

Tests on new samples of PVC pipe (never installed). PVC pipe samples were

received from 16 utilities, representing 10 manufacturers, and in

diameters ranging from 2 to 12 in. All samples passed the fusion qual-

ity (acetone) test. The filler content can be resolved approximately by

determining the density of the sample. This method is not as accurate

as a burnout test, but is simpler to run and is much safer from an

environmental point of view. In determining filler content from a den-

sity test, the possible error is on the order of  2 percentage points.

For example, if the filler content as calculated from the density test is

determined to be 5 percent, the actual percentage of filler could range

from 3 to 7 percent. Burnout tests were run only where there was

some question in results as determined from the density tests or

where the filler content, as calculated, appeared to be abnormally

high. Filler content for pressure pipe should be under 10 parts by

weight, which is about 9 percent by weight. Results from these tests

are given in Table 7.15.

A test specimen from each sample of pipe supplied by the utilities was

prepared and tested to the energy level specified in ASTM D 2241. While

there is no impact strength called out for AWWA C900/C905 pipe, it was

decided to impact the samples to the energy level for the specific diam-

eter as listed in ASTM D 2241. The results of these tests are given in

Table 7.15. Of the 60 samples impact-tested, all except 4 survived with-

out any indication of structural distress. Many of the PVC pipe samples

that were supplied by utilities were sunburned to some degree. The four

samples that failed the impact test were severely sunburned and prob-

ably failed for that reason.

Conclusions

1. Almost 50 percent of problems that are experienced with PVC pipe

occur in the first year after installation.

2. Material-related long-term problems occurring in PVC pipe are few

and are decreasing with time. This is an indication that these prob-

lems are not a result of aging.

TABLE 7.14 Laboratory Test Results for Pipes with Reported Problems

Acetone tests Filler content tests

Utility Pipe size, Attack/no Pipe size, % by

no. in Sample ID attack in Sample ID weight % by parts

70 2 70-2-1A No attack 2 70-2-1F 15 18

70-2-2F 17 20

70-2-3F 14 16

70-2-4F 14 15

3 70-3-1A No attack 3 70-3-1F 9 10

70-3-2F 9 9

70-3-3F 8 9

4 70-4-1A Attack 4 70-4-1F 9 10

70-4-2F 9 11

70-4-3F 7 8

6 70-6-1A Attack 6 70-6-1F 8 9

70-6-2F 8 9

70-6-3F 8 9

8 70-8-1A Attack 8 70-8-1F 5 5

70-8-2F 11 12

70-8-3F 8 9

166 6 166-6-1A No attack 6 166-6-1F 0 0

6 166-6-2A No attack 6 166-6-2F 0 0

456

TABLE 7.15 Laboratory Test Results on Samples of Pipe Currently Being Installed by Utilities

Pipe

diameter, Passed Filler content Passed

Utility no. in Pipe manuf. Spec./class acetone test percent by weight impact test

115 4 A C900/150 Yes 5 Yes

6 A C900/? Yes 2 No

8 ? C900/150 Yes 2 Yes

10 A C900/150 Yes 1 Yes

12 A C900/150 Yes 1 Yes

138 2 C D 2241/200 Yes 1 Yes

4 B D 2241/200 Yes 15 Yes

6 B C900/150 Yes 6 Yes

8 B C900/200 Yes 6 Yes

10 A C900/150 Yes 6 Yes

12 A C900/150 Yes 7 Yes

6 6 E C900/150 Yes 2 Yes

8 E C900/150 Yes 3 Yes

12 E C900/150 Yes 4 Yes

64 6 F C900/150 Yes 3 Yes

8 F C900/150 Yes 3 Yes

12 F C900/150 Yes 3 Yes

20 2 G D 2241/200 Yes 3 Yes

4 F C900/200 Yes 5 Yes

6 E C900/200 Yes 2 Yes`

8 B C900/200 Yes 5 Yes

12 A C900/200 Yes 7 Yes

150 4 A C900/150 Yes 4 No

6 A C900/150 Yes 4 No

8 A C900/150 Yes 6 Yes

10 A C900/150 Yes 6 Yes

12 A C900/150 Yes 3 Yes

60 4 (A) H C900/150 Yes 3 Yes

4 (B) A C900/150 Yes 4 Yes

6 A C900/200 Yes 3 Yes

8 H C900/200 Yes 1 Yes

10 A C900/150 Yes 5 Yes

12 H C900/200 Yes 0 Yes

457

458

TABLE 7.15 Laboratory Test Results on Samples of Pipe Currently Being Installed by Utilities (

Continued

)

Pipe

diameter, Passed Filler content Passed

Utility no. in Pipe manuf. Spec./class acetone test percent by weight impact test

25 6 B C900/150 Yes 4 Yes

8 B C900/150 Yes 3 Yes

12 B C900/150 Yes 4 Yes

85 6 E C900/150 Yes 2 Yes

8 E C900/150 Yes 0 Yes

12 E C900/150 Yes 3 Yes

70 2 C D 2241/200 Yes 4 Yes

3 I D 2241/200 Yes 3 Yes

4 C D 2241/200 Yes 0 Yes

6 J D 2241/200 Yes 4 Yes

160 2 A D 2241/160 Yes 3 Yes

4 E C900/150 Yes 2 No

6 A C900/150 Yes 5 Yes

8 A C900/150 Yes 5 Yes

50 6 F C900/150 Yes 3 Yes

8 F C900/150 Yes 5 Yes

40 6 F C900/150 Yes 5 Yes

8 (A) F C900/150 Yes 7 Yes

8 (B) F C900/150 Yes 4 Yes

7 2 B D 2241/200 Yes 1 Yes

6 B D 2241/200 Yes 3 Yes

79 6 H C900/200 Yes 2 Yes

8 A C900/200 Yes 2 Yes

151 6 ? D 2241/160 Yes 6 Yes

8 (A) D D 2241/160 Yes 3 Yes

8 (B) ? D 2241/160 Yes 4 Yes

10 F D 2241/160 Yes 3 Yes