Reflections of HVAC pipe without Metallic map

[Alexandre Scratch]

Hi everyone

I'm facing a challenge to create the texture of models with metallic map for a game that somebody asked me.

I know that Substance Painter is designed for PBR materials, but I use it to create assets for video-game engines like Source and with using it since years, I never really had any issue or trouble to get what I want with correct and faithful looking into game's engines. I only think about this question today because I work on a model that highly, well mostly only use metallic map (HVAC pipe) and I have difficulties to achieve realistic visual.

Basically, I try to achieve something like this:

I know that something similar is possible on this engine, because I already saw it in the game, so now the question for me is 'how', by 'cheating' without the metallic map. Otherwise, maybe merging basics reflexions to the diffuse map.

Any help or advices are welcomed! 

Thanks