cleaned surface of the drainage ditch pipeline using the strain gage welder system and the portable 115 volt generator 3 the strain gage was connected to the portable strain indicator which in turn was connected to the portable strip chart recorder at the drainage ditch pipeline site 4 via radio from the drainage ditch pipeline site an operator at one of the dow facilities was instructed to lower and then raise the pressure in the line connecting the two dow facilities by 50 pounds per square inch using a compressor located at that facility the 50 psi pressure changes were derived using the following criteria a strain change of 20 microinches per inch would clearly show up on the drainage ditch pipeline strain gage and accompanying equipment and a pressure change of 50 psi was calculated to produce this 20 microinch inch strain according to the following rule of thumb formula equ1 5 the operator at the dow location lowered the pressure of the pipeline connecting the two dow facilities and a strain change of 16 microinches inch was detected on the pipeline at the drainage ditch site the dow operator then raised the pressure by 50 psi in the pipeline connecting the two dow facilities and the strain gage equipment attached to the drainage ditch pipeline showed an increase of 16 microinches inch this correspondence of strain change in the pipeline at the drainage ditch site to the 50 psi pressure changes in the pipeline connecting the two dow facilities positively identified the two as being the same pipeline hence when the pipeline connecting the two dow facilities was subsequently emptied and purged from the dow facility sites the workmen at.