# Affine open with an irreducible complement

Let $$X$$ be an integral scheme such that the morphism to $$\mathrm{Spec}(\mathbb{Z})$$ is proper. Assume the morphism to $$\mathrm{Spec}(\mathbb{Z})$$ has well-defined relative dimension and that the relative dimension is strictly positive. Can you give an example when there is no non-empty affine open with an irreducible complement?