The high-pressure frontier — Twin Branch's steam claims, tested

1940 – 1949

The trade record, first-hand: The steam plant north of the Twin Branch Dam — its industrial course stands in the Industrial Revolution leg — made Mishawaka, for a decade, a place where the country's power engineers were pushing a genuine frontier, and unlike most local firsts this one is documented in the profession's own journal at the time. The Electrical World of 18 October 1941 devoted its issue's lead coverage to the plant: "Twin Branch Innovations Discussed by Designers." Philip Sporn, vice-president and chief engineer of the American Gas & Electric Service Corporation — the system's engineering chief, writing about his own project — titled his account "Twin Branch Extends High-Pressure Economies." The unit the designers described was built for steam at 2,500 pounds' pressure and 940 degrees, with reheat to 900 degrees: "Single-unit assembly of Twin Branch boiler for steam generation at 2,500 psi., 940 deg. F. with between-unit reheat to 900 deg. F." Within the first twenty-four hours of starting, Sporn's colleagues recorded, the operating pressure was brought to 2,700 pounds at the popping valves. The engineering program continued after the war: an American Society of Mechanical Engineers paper of the late 1940s describes the 525,000-kilowatt program of additions at the system's Tidd, Philip Sporn and Twin Branch stations, Twin Branch among the stations built around the 2,000-pound, 1,050-degree reheat cycle the paper sets out. On the trade record, then, this much stands without any company's advertising: in 1940–41 Mishawaka's steam plant was designed, built and written up by its own engineers as the system's high-pressure proving ground, at pressures the profession itself treated as the frontier of commercial practice.

The claims, at their carriers' strength: Two "world" claims ride on that record, and this entry prints both with their carriers named. Of the plant's third unit, added in 1940–41, the city's history writes: "according to a company publication, 'the world's first generating unit to utilize steam pressure as high as 2,400 pounds per square inch in the commercial production of electric power.'" The carrier is a company publication — the utility's own — and the claim is printed as its claim. It sits beside the trade record without contradiction but not as the same fact: the designers' journal describes a plant designed at 2,500 pounds; the company's publication frames the first at 2,400 pounds' steam in commercial production, the two figures being the two records' own, printed here unmerged. Of the fifth unit, which came online in 1949, De Kever's verdict carries its own attribution in his sentence: it "held the world's record for operating efficiency by a single unit," I & M later touted — the company's touting, printed as touting — its turbogenerator running at 2,500 pounds and 950 degrees, "the highest pressure (2,500 pounds per square inch) and the highest temperature (950 degrees) in the world," as the same passage gives the company's figures. The settled strength of the whole matter is this: the frontier itself is documented in the engineers' own journal in October 1941; the first and the record are the operating company's words, and they stand in this record as the operating company's words, beside a trade-press account that needed neither word to treat the plant as the frontier.

Sources:

1. Electrical World, vol. 116, no. 16, 18 October 1941 — "Twin Branch Innovations Discussed by Designers": Philip Sporn, "Twin Branch Extends High-Pressure Economies"; "Open-Pass, 2,500-Pound Natural Circulation Boiler"; "Standard Turbine Designs Easily Adapted to 2,300 Psi"; "Heater and Pump Problems No Obstacle to 2,500 Psi"; "Pipe Welds and Valves for Twin Branch 2,500 Psi"; the figure caption "steam generation at 2,500 psi., 940 deg. F. with between-unit reheat to 900 deg. F."; operating pressure brought to 2,700 psi popping pressure within the first 24 hours of starting; Twin Branch "the main generating station of Indiana & Michigan Electric Company."
2. Peter J. De Kever, Mishawaka: A History — the third generating unit added 1940–41, "according to a company publication, 'the world's first generating unit to utilize steam pressure as high as 2,400 pounds per square inch in the commercial production of electric power'"; the five units "each larger and more economical and more efficient than its predecessors"; Unit 5 online 1949, "held the world's record for operating efficiency by a single unit," I & M later touted, its turbogenerator at 2,500 pounds and 950 degrees, given in the passage as the world's highest pressure and temperature.
3. American Society of Mechanical Engineers, "The 2000-Psi, 1050 F, and 1000 F Reheat Cycle at the Philip Sporn and Twin Branch Steam-Electric Stations" (Journal of Fluids Engineering, paper of the late-1940s program) — the addition of 525,000 kW of generating capacity to the Central System at the Tidd, Philip Sporn and Twin Branch stations; the 2,000-psi, 1,050°F initial-temperature, 1,000°F-reheat design described.