Research program for assessing seismic risks on polyethylene gas pipelines

 

Papers # 2016 Berlin

Representative earthquake loadings have been reproduced in the ENGIE Lab-CRIGEN laboratories on three PE grades, including an excavated old PE63 pipe operated during more than 35 years. Dynamic loading does not alter the pipe residual performances for the three PE families tested, as shown by both the hydrostatic pressure tests and the Phased Array Ultrasonic Technique evaluation. Bending tests do not alter the remaining performances of the PE80 and PE100 families, which comply with the standard requirements. Conversely, the excavated 35-year old PE63 pipe doesn’t meet the requirements anymore although no immediate failure occurred. Moreover, the reduced failure times obtained under accelerated pressure tests suggest a remaining life of about five to ten years. As a summary, these tests show a very good behavior for the main straight lines which is the scope of this working group. As a prospect, the behavior of singular points like service pipes, fittings, tees, etc. has to be explored further to complete the scope regarding PE networks.

The French Association for Earthquake Engineering (AFPS in French) edited last year new guidelines dedicated to evaluate seismic risks for steel buried transmission pipelines. This work has been done in cooperation with the gas operators and the French Regulator as earthquake regulations have been recently evolving. Today, another group has been constituted and is aimed at making guidelines dedicated to distribution pipelines and especially polyethylene pipes which are made of a visco-elasto-plastic material quite different from elasto-plastic steel. This group entails seismic experts, PE experts and the French distribution operators (GRDF) who own around 160,000 km of PE pipes. Thispaper presents the first part of the guidelines which are: an exhaustive earthquake feedback for distribution pipelines ; the seismic loading relevant to distribution pipelines in the French context ; the computational models developed at ENGIE Lab-CRIGEN and the tests program which was performed during the work.The test program consists on the one hand in performing dynamic loading of PE pipes under pressure to simulate the vibratory part of the earthquake. On the other hand, pipes are submitted to imposed displacements to simulate faults or liquefaction-induced movements. Both series of pipes are then submitted to 80°C-hydraulic pressure tests in order to evaluate their remaining performances. The tested 110 mm PE pipes belong to the three representative families PE63, PE80 and PE100. The former one was operated during 35 years and the two others came from the CRIGEN stock. All these tests are completed with non destructive control performed by means of phased-array ultrasonic technique (PAUT) on the pipes, before and after the different loading sequences.

Related keywords : Polyethylene (PE), Earthquake, Seismic loading, Phased Array Ultrasonic Technique (PAUT), Hydrostatic Pressure Test (HPT), Four-point bending test, French Association for Earthquake Engineering (AFPS), French Gas Association (AFG),.
Please note that the whole article content is available on PPCA website onlySource : 2016 Berlin


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