Most of the DM plants have bulk Hydrochloric Acid storage tanks(33% concentration) which are internally rubber lined on carbon steel shell. Generally, to assess the rubber lining condition , i.e, whether hardening of rubber and brittleness has taken place-these tanks are opened within 1-2 years. Is there any NDT method to detect the rubber lining condition without opening the tank? The same query is also extened for internally rubber lined pipes, which carry acidic water in DM plants- as external inspection or selective UT at bends,straight sections does not reveal the internal condition of the pipe where rubber has failed.

Arnab Spark testing using high volatage (conical / round brushes, fine tip holders are used for spark testing) is one of the oldest and still the best N.D.T to detect spark gaps developed in rubber lined pipes / tanks (in other words pin hole leaks develop in rubber lined tanks and pipes which will corrode the pipe bare metal or tank steel shell at localized portions or spread widely if left undetected ). Spark testing is a well known N.D.T in vouge for the last 40 years for D.M. plant tanks and piping. Another method is to assess local hardness check with hand-held rubber hardness tester to D scale - depending on the condition in which rubber lined tanks / piping has been supplied (pre vulcanized cold bond technique, semi ebonite or full ebonite conditions). This includes internal fixed support spargers or nozzle spray used for HCL or H2SO4 injection in D.M. plant tanks which are also rubber lined in previous years (now replaced by polypropylene spargers). UT thickness on outside using a corrosion profile mapping will help you to assess the external steel shell thickness where localized pin hole leaks had develped and corroded the shell due to leaking dilute acid from pin hole leaks or rubber deterioration over years. This is still the best method of N.D.T for rubber lined or FRP lined vessels used for D.M. Plan piping and tanks. Inspecting the D.M> plant rubber lined tanks / piping once in a year is more or less the indsutry standard or industry norm to assess the damage of pin hole leak development in rubber lined pipes / tanks Trust this is of help to you C.V.Srinivasan Nishi Engineers Pvt Ltd India March 28, 2006 E-mail: nishi@vsnl.com >Most of the DM plants have bulk Hydrochloric Acid storage >tanks(33% concentration) which are internally rubber lined >on carbon steel shell. > >Generally, to assess the rubber lining condition , i.e, >whether hardening of rubber and brittleness has taken >place-these tanks are opened within 1-2 years. > >Is there any NDT method to detect the rubber lining >condition without opening the tank? The same query is also >extened for internally rubber lined pipes, which carry >acidic water in DM plants- as external inspection or >selective UT at bends,straight sections does not reveal the >internal condition of the pipe where rubber has failed.