Laboratory investigations on the quality of leak tests and visual inspections of wastewater connection pipes carried out by specialist contractors

In addition to stability and operational safety, leak tightness is the permanent functional objective of wastewater pipes. Tests to determine the tightness of wastewater pipes can in some cases produce results that are worthy of discussion. Therefore, laboratory tests were carried out by 29 specialist contractors to obtain results on the quality of leak tests and visual inspections of connection pipes. The results showed that different test errors can be observed for leak test methods (air overpressure, air underpressure and water pressure). However, only in the case of the water pressure tests did the observed test errors occasionally lead to incorrect test results, i.e. the ‘leaking pipe’ was tested as ‘test passed (tight)’. The investigations into the accuracy (trueness and precision) of the test methods showed that all test methods examined were sufficiently accurate to determine the tightness of the connection pipes. In general, correct test results were achieved if the expert testers did not make any serious test errors and the test equipment used functioned properly. In contrast, the investigations on the quality of visual inspection showed that the procedure is not sufficiently reliable to fulfil all normative requirements regarding damage detection and naming as well as damage classification.

Evaluation of testing procedures for real-scale sewage pipes

Tests to determine the tightness of wastewater pipes can in some cases produce results that are worthy of discussion. Therefore, testing procedures for real-scale sewage pipes used for house connections were evaluated and data was statistically analyzed. The results of the investigation showed that leaky pipes are detected with a very high degree of reliability by all leak test methods. The test methods are also robust against errors by expert testers and deviations from the test specifications. In contrast, tight pipelines can also be incorrectly classified as ‘leaking’ (test failed) to a significant extent during leak tests. Even for the more reliable test methods, i.e. air overpressure, air underpressure and water with low test pressure, a tight pipe is incorrectly classified as leaking (false positive) in one out of ten cases (10%). The highest false positive rate was 20% for water with high test pressure. In addition to the leak test methods, the quality of the visual inspection was also analysed. Here it was found that visual inspection is not sufficiently reliable for determining the tightness of pipelines above the groundwater level. Error rates of approximately. 50% were found for the detection of tight and leaky pipelines.

Numerical Analysis of Nuclear Facility Reinforced Concrete Wall and Roof Slab Behavior Under Close-in Explosions

With the change of anti-terrorism situation, civil unmanned aerial vehicles carrying small equivalent of explosives may cause damage to the reinforced concrete wall or roof of nuclear facilities at close range. Existing research has mostly focused on the overall damage caused by large equivalent explosives at medium and long distances. In this paper, the air overpressure peak curve and behavior of reinforced concrete slabs under small equivalent TNT close-in explosion conditions are calculated by numerical simulation methods and compared with empirical formulas and experimental results in the literature to verify. Furthermore, the numerical simulation method was used to evaluate the resistance of 300mm thick reinforced concrete slabs to close-in impacts of different mass TNT at a standoff distance of 0.4m.