Reading about NASA testing the SLS (Space Launch System) booster and they are chilling it to 40 degrees Fahrenheit. This confused me because they are going to fill it with liquid oxygen and liquid hydrogen which are extremely cold (LOX is 90K, hydrogen is 20K). So I'm thinking maybe the booster has insulated walls. And since one of the tanks is above the other, there must be a pipe to carry the the fluid to engine. So where is this pipe located? And how big is it? And is it insulated as well?
This number and description probably comes from the Wikipedia Space Launch System article and it refers to the two solid fuel boosters attached to the sides of the main core.
Solid fuel boosters do not use cryogenic (very cold) fuel, using solid fuel instead. And so, the temperature testing required is only that which covers the ambient temperature of the launch site.
For SLS, cryogenic fuel is used for the core and upper stage.