I take it that you think there is no such guarantee.How can they guarantee their pipes for 50 years when they haven't been in general use for 50 years.
Was your capability for joined up thinking removed at birth, or has someone beaten it out of you?
Has it never occurred to you to wonder how a car manufacturer can give a 12-year corrosion guarantee on a brand new model of car?
Can you not think (for yourself) of one single way that a manufacturer can afford to offer a long guarantee on a brand new product?
Here's another conundrum:- when you'd been trading for less than six years, how do you think that you were able to offer a six-year guarantee on your professional workmanship?
And before you even contemplate claiming that you didn't, let's just fast-forward to what I'd reply to such an ill-informed contradiction.......
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You're wrong.