Syed Adnan Hussain Piping inspection frequency for a process fertilizer plant is to be determined by: considerations of process conditions (pressure, temperature, material used, velocity, restrictions - valves, orifice plates, straight pipe available after orifice plates or pump or Flow control or temp control valve down stream, likely gas-liquid mixture and their effects, likely gas-gas mixture, likely liquid-gas (vapor vs vapor -liquid transitions), down-stream of relief valve vent piping etc Piping inspection frequency is also governed by compliance to statutory rules (Factories Rules, Explosion Rules) in addition to piping code prevalent in your country. To start with a team comprising your plant's design, inspection and process people should sit together and evaluate all critical points or bends or straight line for each of the process system given by you to make a total over-all programme for monitoring lines in each of the process system. Once you have made an over-all list for each of the process system, then monitoring starts on a systemmatic plan for monitoring - both on stream where possible (where high temperature and insualtion removal is not needed) and during shut-down period of each process stream sections in your plant. UT thickness is the most commonly adopted technique for plotting or knowing the corrosion profile (thickness reduction) in each of the process piping and the critical areas selected for the first "on-line and shut down monitoring schedules". This alone may not be suffice - for a big process plant predictive and preventive inspection scheduling. Supplementary NDT technique inspection by Visual, DPT, MPT, RT, AET, Metallography etc may be needed on selective basis to support and come to a reliable predictive and preventive system. Based on this first monitoring of all critical pipelines in each of the process stream section in your fertilizer plant, second confirmatory monitoring schedule of both the first critical monitored areas in the piping system and also cover additional areas in the same piping process stream sections to evaluate the over-all corrosion pattern - since 100% monitoring is not possible. Once first and second confirmatory tests of all critical areas have given verifying and reliable data, then additional monitoring of other to be done areas can be decided over a period of two or three successive inspections. Generally, this should be accomplished in a way - usually within a four year schedule - that it will meet to both statutory rules compliance in your country (Pakistan) and also establish fool-proof with reliability in monitoring critical areas (it could be bends, elbows, down stream of control valves or orifice plates), high velocity impingement areas, gas-liquid mixture generation areas - where piping system might be designed for liquid velocity but may not be designed adequately for gas-liquid impingement etc. For EX: Carbamate lines, Carbamate/MDEA process lines are prone for both liquid and liquid-gas velocity changes. These engineering principles (guidelines) - if followed systemmatically and in a methodical way - should help any user to evaluate any process pipeline and critical areas in a reliable predictive corrosion monitoring for your fertilizer plant or for any refinery or petro chemical complex. Hope this helps you to evaluate well all critical lines in your plant with your own team or with the help of consultants (if your in-built team lacks in experience) in your country. C.V.Srinivasan Nishi Engineers Pvt Ltd India Feb 15, 2008 E-mail: nishi@vsnl.com >Engro Chemicals is the leading Fertilizer Manufacturers of >Pakistan, >here I >work as an inspection Engineer and my job is to ensure >mechanical >integrity >of plant equipment. We have recently started an exercise to >benchmark >the >inspection frequencies of our plant piping with other >industries. > >Below you will find piping with inspection frequency at >Engro. We >usually >do Ultrasonic thickness monitoring of piping. For burried >piping we use >to >excavate and perform thickness monitoring after removing >coating/wrapping. >Kindly suggest what should be the frequency of inspection of >the >following >piping services based on the existing frequencies at your >plant or based >on >your experience. > >1. ACID LINES >...............................................1 year >(frequency at Engro) >2. CAUSTIC LINES ......................................1 >year (frequency >at >Engro) >3. CATACARB/MDEA ................................2 year >(frequency at >Engro) >4. RAW WATER LINE (burried) ..............1 year (frequency >at Engro) >5. EFFLUENT LINE (burried) .................. 1 year >(frequency at >Engro) >6. GAS LINE FROM FIELD(burried) ...... 1 year (frequency at >Engro) >7. LIQUID AMMONIA LINES ....................Frequency not >defined in >Engro >8. CARBAMATE LINES ............................Frequency not >defined in >Engro >9. PROCESS LINES ..................................Frequency >not defined >in >Engro >10. FUEL GAS LINES ............................... Frequency >not defined >in >Engro >11. SYNTEHSIS GAS LINES ................. Frequency not >defined in Engro >12. CHLORINE GAS LINES..................... Frequency not >defined in >Engro >13. UREA+AMMONICAL WATER ........ Frequency not defined in >Engro >14. PURGE GAS PIPING ..........................Frequency not >defined in >Engro > > >Your valuable inputs will help us to reconcile the >frequencies of the >same. > > >Regards, >Syed Adnan Hussain