Is there any direct correlation method is available to calculate the pipe wall thickness using fluid temperature and pipe skin temperature to calculate the remaining wall thickness.?We have observed process fluid temperature around 505 Deg.C and the pipe skin temperature around 469 deg.C.What is the drop in temperature per mm thick of pipe?Pipe material is low alloy steem(P11). Regards,

Krish Piping code is for design temp and design pressure for a particular material. This usually takes into account the process fluid /service design temperature and design temp (from internal temperature conditions) and not from working /operating pressure or operating temperature conditions. Piping design does not take into consideration the drop in skin temp variation between inner and outer wall (due to thickness). For remaining wall thickness calculation, you have to calculate from design conditions, thermal transients in the system, cyclic loading due to factors of shut down /upset in plant opertions, known Corrosion pattern expected in piping, metallurgical variations expected in material after prolonged exposure at design conditions. Piping designer does not take int consideration any allowance from Maximum working pressure and maximum working temperature (from operational point for a particualr process service) while designing. API 530 recommended guideline would be useful for assessment (as pointed by Luis). Small extraulations is possible for some extended life for wall thickness allowance if variations in skin temp and internal temperture of pipe is not significant. Trust this is of help to you C.V.Srinivasan Nishi Engineers Pvt Ltd India Nov 18,2006 E-mail:nishi@vsnl.com >Is there any direct correlation method is available to >calculate the pipe wall thickness using fluid temperature >and pipe skin temperature to calculate the remaining wall >thickness.?We have observed process fluid temperature around >505 Deg.C and the pipe skin temperature around 469 >deg.C.What is the drop in temperature per mm thick of >pipe?Pipe material is low alloy steem(P11). > >Regards,

Krish Suggest : UT thickness using a high temperature silicon grease (standing to 500 deg cent is available in Indian market or from Krautkramer or Panametric or Sonic type instruments) with a high temperature delayed sensing probe can be used to know the wall thickness. Such delay high temperature sensing probes with special shoes to fit the probes are available with Krautkramer or Panametric type instruments. The basic requirement for high temperature probe use in hot lines of 500 deg cent is that operator using such high temperature probe should be experienced to take accurate readings and without keeping too long a time to record thickness. YOu should fairly reliable and consecutive record to decide on whether a change in wall thickness had taken place even when the plant is in operation. You should be aware of: Limitation with UT delayed high temp probe will be a 10% discount in error in wall thickness readings. This is a well known method to evaluate actual wall thickness in piping in high temperature service. From this you will be able to gauge whether the pipe had internal erosion or wall thickness had reduced considerably. Coke build up will affect heat transfer in piping (no doubt) due to which skin temperature may drop. Coke build up will not cause a reduction in wall thickness (basically). This may affect pipe performance from long term creep or shor term stress rupture properties which can happen even without any wall thickness reduction. Skin temperature measurement using Thermal imaging system and arriving at a corrleation for wall thickness change due to coke formation is not a reliable or fool proof system. Trust this helps you to approach this problem in a practical way than spending time on costly thermal imaging to get unreliable results. C.V.Srinivasan Nishi Engineer Pvt Ltd India Nov 19, 2006 E-mail: nishi@vsnl.com >Thanks for the reply. Due to high operating temperature we >could not measure the remaining wall thickness and we expect >some amount of erosion inside the line.By using thermal >imaging we can measure the actual skin temperature of the >pipeline and by Thermowell(TI Point) real process fluid >temperature can be measured.By using these two temperature >whether we can calculate the amount of coke build-up by heat >transfer method and drop in temperature per mm thickness of >coke.Suppose if heavy amount of coke build-up is there the >skin temperature will drop due insulating layer of coke and >also if the tube wall thickness is less, the amount of heat >transfer will be more compared to the original thickness of >material since the rate of heat transfer is proportional to >wall thickness of pipe.For your comments please.