You may look to the other parts of EN 14620;
BS EN 14620 part 1 is for general ,
BS EN 14620 part 2 is for metallic components,
BS EN 14620 part 3 is for concrete components,
BS EN 14620 part 4 is for insulation components,
BS EN 14620 part 5 is for testing, purging, cool down ..
If necessary, a hybrid approach should be considered .( API+ EN 14620 )
I do not understand your position ..
LNG tank business is highly specialized area and some companies have in house standards and details..
Tim was so learned that he could name a
horse in nine languages: so ignorant that he bought a cow to ride on.
(BENJAMIN FRANKLIN )