Krish Helical springs are known to fail by tension - torsion and by fatigue failure also. Pitting seen in your spring might have accelerated the failure - as pits act as stress raisers either in tension or torsion or in fatigue corrosion. Chattering seen due to upset in plant might have accelerated or contributed to higher tension-torsion related effect. In ASM Source book on "Failure Analysis" two case histories of helical spring failures and diagnosis have been clearly outlined - though the failed helical springs were not related to hydro carbon service. Safety valves have to be tested annually - as per SMPV(U) Rules 1981 - if the SRV is in LPG/Propane service for pop-up pressure as well as to check condition of spring and valve seating. In an operating refinery, SRV's have to be tested during major shut down or during shut down time also - atleast those are in critical service Safety valves. If such testing had been done regularly, pitting noted in spring would not have gone undetected in so many years. Hope this helps C.V.Srinivasan Nishi Engineers Pvt Ltd India Sept 3,2007 E-mail: nishi@vsnl.com >We have noticed safety valve spring failure in hydrocarbon >service which is in operation for more than 15 years.We have >noticed substantial corrosion (pitting)on the spring.The top >and bottom helix portion got fractured.The fractured surface >is in oval shape.What could be the reason for such >failure?What type of failure can be expected in the above >service?Before brought into test bench the subject valve was >chattering continuously for about 30 minutes due to plant >upset. > >regards,