Water Pressure Testing

The classical method of leaktightness testing provides for pressure testing with water as the test medium (Abschnitt 4.5.1.1).

It is specified for the leaktightness testing of newly laid drains and sewers that are operated as gravity pipes, for the countries of the EU in EN 1610 [DINEN1610b] within the scope of the construction acceptance and indirectly in EN 752-5 [DINEN752-5b] also for the acceptance of rehabilitated sewers.

The test itself must be carried out on the already backfilled piping. As in this case the optical inspection of the external pipe walls is impossible, also "Initial testing may be applied before any sidefill is placed. For the final acceptance the line shall be tested after backfilling…" [DINEN1610b].

For testing purposes, all openings of the affected pipe section of the sewer including all branches and inlets must be closed off in a watertight and pressure tight manner. Subsequently the pipe is continuously filled with water from the lowest point of the pipe slowly enough that at a sufficiently largely dimensioned vent point at the highest point of the pipe that has at least the same cross sectional area as the fill pipe, the air in the sewer can escape (Image 4.6.2.3.4-1). The sewer section may at no time have a direct connection to a pipe - hydrant or pump - that is under pressure. The filling and the application of pressure must occur via a vessel under gravity. A sufficient period of time is to be provided between filling and testing the pipe (pre-fill time) to allow the remaining air in the pipe to finally escape and, if required, to soak the pipe walls sufficiently with water [DINEN1610b].

The pre-fill time that is made dependent of the pipe materials in many international standards (Table 4.6.2.3.4-1) is generally limited to 1 hour. In exceptional cases, in case it is necessary due to special climatic conditions, it can be extended to 24 hours.

"The test pressure is the pressure equivalent to or resulting from filling of the test section up to the ground level of the downstream or upstream manhole, as appropriate, with a maximum pressure of 50 kPa and a minimum pressure of 10 kPa measured at the top of the pipe. Higher test pressures may be specified for pipelines, which are designed to operate under permanent or temporary surcharges" [DINEN1610b].

The pipeline is judged to be watertight when the water addition required to maintain the test pressure of 0.15 l/m² of wetted pipe inner surface is not exceeded during the testing period of 30 minutes (Image 4.6.2.3.4-2).

With regards to the permissible water addition value, EN 1610 [DINEN1610b] has disassociated itself from the previous dependence on the piping materials in the international standards. The water addition values given as an example in (Table 4.6.2.3.4-1) under DIN 4033 [DIN4033b] were experience values that were the result of material conditions of differing water absorption of the pipe wall as well as the compacting and slow escaping air trapped in the crown area, in the wall thickness and in the joint spaces of the pipe.

Leaktightness testing of newly laid drains and sewers in water catchment areas (Abschnitt 6.1) must be carried out in the Federal Republic of Germany in accordance with ATV-A 142E [ATVA142a]. This requires that, contrary to EN 1610 [DINEN1610b], the testing be to be carried out on the exposed section of the sewer so that exfiltrating water is optically visible. The test pressure is 0.5 bar measured at the highest point (pipe crown) of the sewer to be tested. If a higher pressure is possible because of a backwater event, then this pressure will be applicable to the testing.

If the watertight testing, however, can only be carried out after the backfilling of the pipe trench, then a stricter pressure testing is required according to the specification of the Bayerischen Landesamts für Wasserwirtschaft (Bavarian State Department for Water Supplies) [Bayer92]. In this, the test is carried out in two test intervals of 15 minutes each, in which the water addition for maintaining the test pressure is measured. In order that the object to be tested can be judged to be leaktight, the measured water addition of the second test interval must be less than the first, whereby both water addition values must not exceed the permissible limits of the DIN 4033 (Table 4.6.2.3.4-1). The test time is doubled from 15 minutes to 30 minutes.

If moist places on the pipe wall are found during the test, or individual drops at the pipe or on the outer walls of the manholes, then the tests must be stopped for changing the defective parts. The test must then be repeated. For sewers of double walled piping, the sewage pipes and the jacket pipes must be tested separately.

Examples of execution for training of and installation of double-walled pipes or single walled drains and sewers, as well as testing methods for controlling leaktightness are summarised in ATV-M 146 [ATV95b] (Abschnitt 6.4.2.1).

The testing of existing drain and sewer systems that are already in operation is regulated in the Federal Republic of Germany by ATV-M 143 Part 6 [ATVM143-6]. Here, an addition of water of 0.2 l/m² of wetted inner pipe surface per test time of 15 minutes independently of the pipe materials is permitted for water pressure testing. The test pressure is 0.05 bar - comparable to a water height of 50 cm at the highest point of the object to be tested (Image 4.6.2.3.4-1).

In comparison to EN 1610 [DINEN1610b] (Image 4.6.2.3.4-2), the test time has been reduced to 15 minutes in order to minimise the required time the object to be tested is out of use. Taking the danger potential of the exfiltrating test water (e.g. bedding alterations due to flushing the soil particles (Abschnitt 2.2.3.1) (Abschnitt 2.2.3.2) and [Stein97g] [Stein96b], the test pressure in ATV-M 143 Part 6 [ATVM143-6] has also been substantially reduced in comparison to EN 1610 [DINEN1610b], whereby the following aspects have been taken into account:

• Because of the lower test pressure, the danger potential mentioned above caused by exfiltrating test medium is minimised.
• Through the selection of a defined test pressure of 0.05 bar, the absence of air in the sewer to be tested is ensured, on the one hand, and, on the other hand, the comparability of the test results are ensured;
• The leaktightness of the drains and sewers can be sufficiently ensured under operating conditions if the permissible water addition has been adhered to. For overflow events, which are the maximum internal pressure loads for gravity piping, there usually only occur flows of diluted sewage or lightly contaminated surface water. This loading occurs less than once a year for hydraulically amply dimensioned sewers (Table 4.6.2.3.4-1). A possible loading of exfiltrating sewage in this case can be accepted from the point of view of open water or soil protection [Stein97g] [Stein96b].

Image 4.6.2.3.4-1:  Section or sector leaktightness testing with water as the test medium - testing criteria to ATV-M 143 Part 6 [Image: S&P GmbH]

Image 4.6.2.3.4-2:  Section or sector leaktightness testing with water as the test medium - testing criteria to EN 1610 / ATV-A 139 [Image: S&P GmbH]