LPG. Vessels. Small LPG fixed tanks are not part of the Pressure Vessel Regulations. And as such do not require examination under any H&SE requirement. Unlike the much larger commercial and domestic fixed tanks, which are provided with the means of access for this purpose. This was the position in 1998 when I retired as a surveyor and pressure vessel examiner, and as far as I know is still the case. Portable Vessels are like-wise not covered. Generally the likes of Calor etc; will check and do periodically test them but the scale of exchanges makes it far more likely that whilst they may change the odd valve unit and a physical external check and Re-paint, that is about the size of it, if it looks at all dodgy it gets scrapped. Refillable gas cylinder retailers or manufacturers recommend a 10 year life. But this is largely arse covering on their part. For which you cannot blame them. What I can say with some confidence having inspected all 3 of those on my R-V`s over time, is that the only thing(s) that needs checking are the fastenings, and the external parts for corrosion. I also check any welding for defects, but that is ingrained habit. And to ensure the 80% fill devices actually work. I did take the opportunity when one of mine had to have the contents gauge replaced to examine the inside, using an endoscope, at better than 12years old, I could have eaten dinner off the surface. To my knowledge, there are 80`s American R-V`s, with tanks that have never been opened up nor otherwise tested.
Pete