Dear Deenajag,
Certainly the work undertaken for ONGC of repairs of pipelines will fall under the scope of meaning Building and other Construction Work and if you engaged more than 10 workers on this work, you need to obtain RC under the Act.
Please read the definition of "building or other construction work" section 2(d) which clearly says that "building or other construction work" means the construction, alteration, repairs, maintenance or demolition, or, in relation, to buildings, streets, roads, railways, tramways, airfields, irrigation, drainage, embankment and navigation works, flood control works (including storm water drainage works), generation, transmission an distribution of power, water works (including channels for distribution of water), oil and gas installations, electric lines, wireless, radio, television, telephone, telegraph and overseas communications, dams, canals, reservoirs, watercourses, tunnels, bridges, viaducts, aqueducts, pipelines, towers, cooling towers, transmission towers....