De acordo com o National Electrical Code, o tubo tem que ser ligado. No entanto, ele pode ser ligado usando o condutor de aterramento que atende ao equipamento que usa o gás.
...The equipment grounding conductor for the circuit that is likely to energize the piping shall be permitted to serve as the bonding means...
Quanto a um raio, a companhia de gás provavelmente está correta. Não é provável que um raio caia no cano, especialmente porque fica bem ao lado de uma casa.
National Electrical Code 2014
Chapter 2 Wiring and Protection
Article 250 Grounding and Bonding
250.104 Bonding of Piping Systems and Exposed Structural Steel.
(B) Other Metal Piping. If installed in, or attached to, a building or structure, a metal piping system(s), including gas piping, that is likely to become energized shall be bonded to the service equipment enclosure; the grounded conductor at the service; the grounding electrode conductor, if of sufficient size; or to one or more grounding electrodes used. The bonding conductor(s) or jumper(s) shall be sized in accordance with 250.122, using the rating of the circuit that is likely to energize the piping system(s). The equipment grounding conductor for the circuit that is likely to energize the piping shall be permitted to serve as the bonding means. The points of attachment of the bonding jumper(s) shall be accessible.