Drop weight impact testing of samples for evaluating the fracture toughness of welded gas and oil pipes

Abstract

The analysis of the drop weight impact equipment used to evaluate the fracture toughness of welded gas and oil pipes by the criterion of fiber in the sample fracture was made. Drop Weight Impact Testers used at Russian pipe and metallurgic plants are exported machines from foreign firms Instrom, Imatek and others. In Russia such testers are not produced.

Some Drop Weight Impact Testers (Imatek company) have the option of automatic recording of sample destruction and allow determining the maximum destructive load, energy parameters of destruction (total work of fracture, the specific work of crack propagation), the velocity of crack propagation. This allows using the equipment to implement the method for quantitative evaluation of fracture toughness for gas and oil pipes. Drop Weight Impact Testers are equipped with cooling chambers for cooling samples up to -80 C and with a device to make cuts on samples. Drop Weight Impact Testers allow to test samples of high-strength steel up to K100 with thickness up to 50 mm. Testers of Imatek have significant advantages over the testers of Instrom: they show higher productivity, they have computer system to register fracture parameters, they can test specimens of steel with the durability equal to K100 and above and with the thickness of up to 50 mm.

The destruction of a large sample similar in geometry to DWTT sample was made using Drop Weight Impact Testers. The complex nature of fibers in the fracture of the specimen under dynamic load was determined. It depends on the viscosity of the material, on the speed of cracks in the sample, on the flexibility of loading system. Without correcting DWTT samples it is not sensible to use these samples to conduct acceptance tests for the evaluation of fracture toughness of welded gas pipes.