Not sure of many companies that design. I myself am a pipefitter welder on military base. We use steam year round and have four big steam plants and steam generator. We are a group of four that do the repairs and replacement of steam, condensate and traps. If we need some help on big jobs we use JCI, KBR and R. Brooks. Maybe one of them can help you? We use schedule 80 and 120 in troughs and underground. Good luck in your search
Jay pm me and I will give you a list of my mechanical design engineers and contractors that design and maintain our high pressure steam systems. I manage a hospitals high psi steam plant.
Hospitals and processing plants are Most likely the largest users of steam plants aside from utility company’s. These days.