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Qualification Testing

 

 

Strain Corrosion Testing

A unique and important performance requirement for glass fiber gravity pipe used in sewer applications is the chemical testing of the pipe in a strained condition.

This strain corrosion testing is carried out in accordance with ASTM D3681. and requires a minimum of 18 ring samples of the pipe to be deflected to various levels and held constant.

These strained rings are then exposed at the invert of the interior surface to 1 NO (5% by weight) sulphuric acid. This is intended to simulate a buried septic sewer condition This has been shown to be representative of the worst sewer conditions including those found in the Middle East.

 

The time to failure (leakage) for each test sample is measured Failure times must meet a specified distribution, with at least one occurring after 10.000 hours (over 14 months).

 

Bending tensile strains are plotted against time to failure for each of the test samples using a log scale .The resulting least squares regression line is extrapolated to 50 years.

 

The minimum extrapolated failure strain at 50 years must equal the values shown for each stiffness class. The value achieved is then relatable to the pipe design to enable prediction of safe installation limitations for glass fiber pipe used for this type of service.

 


Stiffness Class
SN

Minimum 50 Year
Bending Strain,

1250

0.60 (t/d)

2500

0.49 (t/d)

5000

0.41 (t/d)

10000

0.34 (t/d)

 

 



Hydrostatic Design Basis HDB

 

Another important qualification test is the establishment of the Hydrostatic Design Basis HDB. This test is carried out in accordance with ASTM D2992 procedure B and requires hydrostatic testing to failure (leakage of several pipe samples at a variety of very high constant pressure (strain) levels These must result in failures varying from within minutes' to at least 10.000 hours As in the strain corrosion test described above.




The resulting data is evaluated on a log bass for pressure (hoop tensile strain) Vs time to failure and then extrapolated to 50 years (See graph at right).

The extrapolated failure pressure (strain) at 50 years referred to as the hydrostatic design basis (strain) or HDB must be at least 1.8 times the pressure (strain) caused by the rated pressure class.

 

In other words the design criteria requires that the average pipe be capable of withstanding a constant pressure of 1 8 times the maximum operating condition for 50 years This qualification test helps assure the long term performance of the pipe in pressure service.



Joint Testing

The third important qualification test is conducted on joint prototypes for elastomeric gasket sealed couplings.

This is a severe test carried out in accordance with ASTM D4161. It incorporates some of the most stringent joint performance requirements in the piping industry for pipe of any material within the pressure and size ranges of Flowtite Pipe ASTM D4161 requires these flexible joints to withstand hydrostatic testing in configurations that simulate very severe in use conditions.

Pressures used are twice those rated and 100 kPa is used for gravity flow pipe. Joint configurations include straight alignment. Maximum angular rotation and differential shear loading. A partial vacuum test is also included.

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