Steelmaker Corus has been fined £250,000 and told to pay costs of £43,000 after the death of a worker at its Trostre plant in Llanelli.
Frank Coles was struck by a metal guard plate
Francis Coles, 42, known as Frank, died when he was struck on the neck by a guard plate in 2003.
The company had pleaded guilty to two breaches of health and safety legislation at Swansea Crown Court.
Speaking after the hearing his mother said the fine was "nothing, but at least he has had justice".
Prosecuting on behalf of the Health and Safety Executive (HSE) Simon Parrington said Mr Coles suffered a fatal blow to his head on 4 January 2003.
The father-of-three had been working as part of a team replacing rollers on a mill used for making strip steel.
A latch pin that would have prevented the plate from falling was not in place, and a switch was faulty.
Mr Parrington said the accident was thoroughly investigated by police and the HSE but it was not known exactly what happened.
Mr Coles's mother, Christine Coles, attended the court case
"Whatever happened it was clear Mr Coles was able to gain access to dangerous parts while (the plant was) live and the system of changing the rolls on the mill was unsafe," said the barrister.
He said need to review risk assessments at the mill had been raised by the works safety committee the previous May but had not been done.
"The company failed to recognise the extent of the hazard," he said.
"The accident was avoidable, it was foreseeable".
Charles Feeney defending said Mr Coles's death was the first fatality at the plant since it opened in 1952.
He said Corus had pleaded guilty at the first opportunity, had settled a claim made by Mr Coles's family in full and had fully cooperated with the police and HSE.
He said since the accident there had been "an enhanced approach" to health and safety throughout the whole plant and steps had been taken to "make sure this type of accident will never occur again".
Mr Feeney said there had been widespread shock at Mr Coles's death as he had worked there for 15 years and he was "well liked and well regarded".
He said Corus had apologised and expressed regret several times before and wished to do so again.
Passing sentence, Judge Justice John Saunders said it was a matter of regret that the case had taken so long to be dealt with.
The judge said he was a much loved son, husband and father.
"The fine which I will impose is not intended in any way to reflect his worth that can never be measured in financial terms."
He said he was sure the accident was not due to Corus's desire to cut costs and he was satisfied the company had co-operated fully and had sped up the process of updating risk assessments throughout the business.
"What was wrong in 2003 has been rectified throughout the organisation but that was too late for Mr Coles," he said.
Speaking after the hearing, his mother Christine Coles said: "He was only 42, in the prime of his life, with three beautiful children.
"For me £250,000 is nothing but at least he has had justice."
In a statement, Corus said it accepted the court's decision in respect of "its failings".
"Health and safety in our working environment is our first priority.
"A fatality such as this is unprecedented in Trostre and has been traumatic to all involved."
It said it was determined to learn from the tragedy and it had reinforced its approach to health and safety.