its a straw inside another straw why could this not have an inflatable rubber seal on the outside of it? Do I have to design every strategy for BP?
Well,...you need to call them for a consulting contract...
Put the seal on the inside of the riser...It’s called a “packer”, and they’ve been in use in the industry for roughly 90 years.
The graphic shown in another thread does indicate a pair of collars to center the suction line in the leaking pipe. It's not clear if those actually help seal the gap or just locate the smaller line at the center (possibly to allow a more secure packing to be fitted as the next step).