There is another ASCE Report "Wind Load on Petrochemical Facilities" (I don't have the document handy, can't tell the verision and date).
A very important aspect in wind load calculation for piperack, I think, is that you need to consider the available width of the rack no matter the pipes are full or not on the rack for the current project. As per this report, you need to consider (D+0.1W)L as the loading area, where D is the maximum pipe diameter at one level, W is the piperack width, and L is the calculation length.