Robbie Williamson, 11, from Burnley in Lancashire, died playing a game of dare with friends on 22 April 2014.
He was using the pipe to cross the Leeds and Liverpool Canal in the town.
At Preston Crown Court National Grid admitted failing to guard the pipeline but said Robbie would have tried to access it if it had been protected.
The Health and Safety Executive carried out an investigation against the utility company which has responsibility for the cast iron pipe attached to Dugdale Bridge, near Lowerhouse Lane.
A post-mortem examination found Robbie died from drowning and a head injury. A verdict of accidental death was recorded at the inquest.
Following his death, National Grid installed protection on the pipe and have carried out a review of all the other pipe crossings it owns.
The firm as pleaded guilty to failing to discharge their duty in ensuring "as was reasonably practicable" the health and safety of others by exposing them to risk of injury.
A Newton hearing has been scheduled to take place on 8 December.
The hearing is held in front of a judge when the defence and prosecution dispute the facts on which the court would impose a sentence.
A utility company has admitted a health and safety breach after a boy died when he slipped from an exposed gas pipe and fell into a canal.