Since I am an advocate of repurposing NG pipelines to carry hydrogen and where needed building dedicated hydrogen pipelines, in fairness I think I should link this study which does not fancy it at all:

https://scijournals.onlinelibrary.wiley.com/doi/10.1002/ese3.1861

I will just note that they are entirely unspecific about what pipes and where, as specifications differ, and that they focus on problems, with no hint of opportunities.
And they assert in their conclusion:

' Considering its physical and chemical properties, hydrogen is not an effective decarbonization tool for use in homes and buildings. For any decarbonization strategy, it is critical to determine if a fuel is in fact needed, and to compare with potentially more effective options such as direct electrification using renewably generated electricity.'

Without the slightest nod to the substantial challenges of directly electrifying everything, perhaps above all the issue of intermittency, which is why engineers turn to hydrogen, as you need something to come through the plug when needed.

I link in the comments here the far more limited study by the National Grid in the UK, which is based on their extensive testing, and makes no claims to universitality, they are talking about the pipeline network for which they are responsible, not whatever they have put in in Rhode Island or somewhere:
https://www.greencarcongress.com/2024/07/20240724-pennstate.html

My view is that the critique of pipeline conversion is a conclusion in search of a rationale, vague, generalised, and glossing over the problems of their unexamined supposed alternatives.

But I am not God, having failed the exam, so YMMV!

I prefer to link and examine critiques, so here you go.