A Brief History of Severn Engineering Company


The Severn Engineering Company was founded in 1952 by Martin Robert Gross and Herman C. Ellinghausen Sr. It continues to manufacture and re-calibrate its Low-Mu Permeability Indicators and its Ferrite Indicators, which are used around the world today.

Severn Engineering was originally created for the purpose of developing and manufacturing a field instrument to test the magnetic permeability of feebly magnetic materials for the U.S. Navy Bureau of Ships. It was used in the Mine Sweeper Program during the Korean War. Mr. Gross and Mr. Ellinghausen were employed as civilians at the U.S. Navy Engineering Experimental Station (later the David W. Taylor Research Laboratory) in Annapolis, Maryland. Their area of research was the magnetic permeability of feebly magnetic stainless steel. The Navy's urgent need for a field instrument to measure magnetic permeability prompted the Bureau of Ships to talk to them about producing such an instrument. After resolving legal issues, Severn Engineering Company was founded and the Severn Gage was designed. The Navy then placed an order for 317 instruments. Other orders soon followed from contractors as well as the Navy.

The Permeability Indicator was first developed and manufactured in 1952. Since its invention, the Permeability Indicator, now called the Low-Mu Permeability Indicator, has undergone only minor design changes, and the Indicator retains its original form today. The standards to calibrate the Indicator were developed by Severn Engineering with help from the Experimental Station and the National Bureau of Standards. These standards are presently still in use. The Indicator had its own Military Specification (MIL-I-17142B) up until 1994 when it was phased out by the military. The Indicator is approved by ASTM A342/A342M-04 as an acceptable method for measuring low magnetic permeability. The Company has since developed its own Specification and Quality Standards for the Permeability Indicator.

The Ferrite Indicator was developed in 1972 to measure the Ferrite content of Austenitic Stainless Steel weld metals. A Welding Research Council Sub-committee was tasked to find a better way to measure Ferrite content of welds. The result was an arbitrary measure called Ferrite Number. The American Welding Society and the industry have accepted this as the standard measurement of Ferrite content in welds. The standards for the Ferrite Indicator were based upon the Ferrite Number. They were designed by the Severn Engineering Co. and Babcock and Wilcox and were produced by Babcock and Wilcox . Ferrite Indicators can be calibrated either by Ferrite Number or by percent Ferrite.