A reformer apparatus 8 has a heat shield 17 for a reformer duct 16. Various construction details which increase the durability of the heat shield are developed. In one embodiment, the heat shield includes a plurality of rings 82 which are axially and circumferentially segmented, the rings being supported by a platform on which the stack of rings rests. At least one of the rings has a pair of segments each of which has a V-shaped identation in the end which receives a V-shaped projection of the adjacent segment leaving a circumferential gap between the segments which does not extend radially between the segments of the ring.