I moved into a new home with laundry room in basement and started to notice occasional wafting of sewer gas out of the laundry drain pipe. It is an older home built ‘58. It looks like there is no p-trap. How could this be? How should I correct it?
You should investigate if the old cast iron pipe has a trap of some sort below the brown tile floor (if there is a basement or crawl space below this floor). In all likelihood there is not such trap present but checking makes sense in case there is some type of failure there.
Since the existing merge of the white PVC pipes to the cast iron piping (via the few shown black fittings) is so close to the floor you may be faced with having to replace some of this white PVC piping. It is probably going to require adding two separate P-Traps, one for the vertical line feed from the washer drain stand pipe and a separate one in line with the horizontal section that currently feeds into the stand pipe. There just does not look like there is room to place a trap below the horizontal to stand pipe Tee.