By Bob LeHunt, John Black and Mike Stahmer
October 2001
Revised April 2004

It has long been recognised that for field pressure testing of PE pipelines it may be necessary to provide allowance for the fact that polyethylene pipes expand under pressure and are subject to creep. Recommendations such as found in Oy Wiik & Hoglund published literature, were developed in Scandinavia over twenty years ago to account for the pressure variations, especially with pipes up to one metre diameter.

In Australia, large diameter pressure pipelines were being field pressure tested as long ago as the 1960’s. AS 2033, Installation of Polyethylene Pipe Systems, first published in 1977, acknowledged the phenomenon, but did not provide specific guidance for making allowance. The main emphasis was on visual inspection of joints for leakage, still the most effective method if practicable.

In the period since, various national and industry specifications have been developed, including WRc (U.K.), ASTM (U.SA.), PPI (U.S.A.) VAV P78 (Sweden), CEN. In addition, the advent of PE materials with higher stress ratings and lower modulus values has necessitated more detailed consideration of the procedures.

Where pipe expansion is a consideration, the method should either account for effects such as soil support or be independent of them. Two methods that are independent of soil support are the modified rebound method, based on work within CEN, and the Swedish Water Works Association VAV P78 method, originally developed by Prof. Lars-Eric Janson. This latter method has been successfully used over a range of pipe sizes since 1989, and described in various publications. The modified rebound method has the advantage that it is a quick test, but it cannot quantify a leak in the event of failure. This method is suitable for all pipe diameters. Where it may be necessary to quantify a leak, or for referee purposes (eg to resolve an inconclusive test result), the method of Prof. Lars-Eric Janson should be used.

Regarding other methods, ASTM rely heavily upon visual inspection, PPI recommendations are similar to rebound and Swedish Water Works Association (but material specific), and the WRc (pressure decay) method is complex and requires an estimate of the support given by the soil.

For pipelines where visual inspection of joints is not practicable, for long pipelines, or for larger diameters, the following are the recommended procedures for field pressure testing.

The Reference Test (Prof. Lars-Eric Janson) method has been adopted by Standards Australia in AS/NZS 2566.2:2002 Buried flexible pipelines Part 2: Installation, and by the Water Services Association of Australia (WSAA) in their Polyethylene Pipeline Code WSA 01 - 2004.

• Water entry at lowest point in line

• Flush/swab/vent all air from line.

MAXIMUM SYSTEM TEST PRESSURE (STP) at least 1.25 times maximum working pressure of pipeline but not to exceed 1.25 times MAOP of lowest rated pipe/fitting in line.

• Reduce pressure to atmospheric, let stand for 60 minutes.

• Raise to STP in less than 10 minutes and hold for 30 minutes, pumping as needed.

• Inspect for leaks, shut off pressure, let stand for 60 minutes.

• Measure pressure reading P₆₀ > 70% STP.

• Quickly (<5 minutes) reduce pressure by 10 -15% of STP - DP.

• Measure water volume bled out - D V

• Calculate D V_{max allowable} if not already done.

• Observe and record pressure rise for 30 minutes.

• No leaks

• No components break

• Pressure reading rises / remains static over 30 minutes. If in doubt, leave for 90 minutes, maximum allowable pressure drop in 90 minutes = 20 kPa.

• Locate and repair leaks
• If failure is marginal or doubtful, or if it’s necessary to determine leakage rate, use Reference Test.

• Water entry at lowest point in line

• Flush/swab/vent all air from line.

MAXIMUM SYSTEM TEST PRESSURE (STP) at least 1.25 times maximum working pressure of pipeline but not to exceed 1.25 times MAOP of lowest rated pipe/fitting in line.

• Raise pressure to STP, close off main, allow to settle for at least 12 hours. The pressure gauge will show a drop.

• Inspect for leaks.

• Raise pressure to STP and maintain for 5 hours.

• Measure water volume to keep constant pressure between 2 hours and 3 hours after test start.

• Measure water volume to keep constant pressure between 4 hours and 5 hours after test start.

• D V_(5h-4h) £ 0.55 D V_(3h-2h) + V_{leak 1h}

• No visible leaks

• No components break

• Repair / reinstate pipeline

For Further information please contact :
Plastics Industry Pipe Association of Australia Ltd
Suite 246, 813 Pacific Hwy, Chatswood NSW 2067
or email plasticspipe@pipa.com.au