Increased corrosion at Sulfuric Acid ALKY in effluent treating section

[SuperDad]

We are currently experienced an increasing corrosion rate at equipment downstream of our Acid wash vessel. The corrosion is manifested by a disproportionately high rate at the welds in our DIB feed line, attacking the metallurgy at a much higher rate than the carbon steel segments of the line. This is a recent phenomenon whose onset may hay have been triggered by the replacement, during our last TAR, of some key equipment due to the recommendation of our consultant. Prior to the replacement of this equipment, we experienced a corrosion rate at an acceptable rate as we were replacing the DIB feed line every 5 years or so. We are currently replacing the line every 6-8 months and have experienced some leaks prior to replacement. Our system is a sulfuric acid line. We've measured the free acid content of effluent from the acid wash w/a 2 to 3.5ppm content. The troubling issue is that we cannot positively identify the corrosion mechanism. We cannot identify any other operational or process difference between current operation and pre-TAR operation. The only difference that we can identify is the replacement of this key equipment. Any insights?