The results of four full-scale burst tests conducted at the test site in Denmark were reported and the required fracture toughness for arrest was discussed for the X80 pipeline used for rich-gas transmission under ultra-high pressure (defined as greater than a 15 MPa internal pressure). The ductile crack arrest behavior was evaluated for buried using well-compacted sand and unburied conditions. The initial internal pressure of the tests was approximately 18.4 and 16.2 MPa corresponding to hoop stress of 400 and 350 MPa (72% SMYS and 64% SMYS), respectively. Natural gas that consisting of 89-90 mol % methane and the balance being heavier hydrocarbons that give the rich-gas compositions was used for the burst tests. The outer diameters of the tested pipes were 762 mm (30-inch) and 610 mm (24-inch). The velocities of the propagated ductile cracks and the rich-gas decompression were determined from the data measured at the sampling rate of 25 kHz. Based on these test results, the required Charpy v-notch impact energy (vE energy) was used as a measure of the fracture resistance for arrest of the ductile propagating cracks evaluated under different backfill depth conditions. The applicability of the Battelle Two-Curve (BTC) approach was also investigated.