I suppose you have to check for the MAWP (maximum allowable working pressure) with your actual real thickness at 950%C2ºC because at that temperature you are working in or near the creep range. If your thickness stands your service pressure at that temperature you can keep going on if no you have to re rating your heater. The usual practice to inspect reformer heaters is as follows: Visual analysis, go-no-go gauge of tubes and measurement of the external diameter of the pipes to search for ovalizing, bends due to distortion, constraints, increases of diameter and pipe length, thickness measurements to evaluate the level of corrosion, with main incidence in hottest zones of the tubes. Radiographic examination to search for cracks and internal corrosion of pipe surfaces, as well as evaluating the existence of internal coke layer and mainly determining the level of incidence of the erosion in the curvilinear zones or flow change of direction. Dye penetrant inspection with intention to detect eventual cracking (essentially of thermal fatigue) in the external surface of the pipes. Perform metalographic replicas to evaluate levels of micro structural degradation of micro voids and micro cracks in the hottest zones. Perform hardness tests to check for softness phenomena such as decarburisation oxidation and evolution of micro structural components spheridoisation and carbonates coalescence or hardening such as carburising mainly from the internal surface of the pipes. Evaluate the amount level of magnetic permeability in the external surface of the pipes decurrently of internal carburisation - a more accurate analysis will have to be carried through rectification of external surface of the suspicious zones of tubes for elimination of the oxidised zone (as it is known, this type of leagues becomes ferromagnetic as, not only by carburisation, but also by oxidation)

Chakra This topic has been raised earlier and responses have been quite good. You could get information from earlier responses. You should be aware that design consideration is different from operational use in a plant (whether it is a pressure vessel, piping, heat exchanger or furnace tubes) Designer takes into account 5 to 10% over normal operating pressure. Paralloy H 39 should be deisgned for 950 deg cent. When we talk of creep and creep related effects to evaluate the remaining life of a reformer tube, we take the effect of third stage of creep ("Tertiary creep) related damages. Creep effect starts from 20,000 hrs onwards. At 910 deg cent of normal operation (if daily log record of Pyrmometer skin temp readings are reliable) then Paralloy H 49 should easily stand 100,000 hr life expectancy a designer gives at 950 deg cent and not at 910 deg cent ( i.e, 12 years of operational life). Paralloy H 39 can technically stand another 50-100 deg cent of excess temperature (more than design temp of 950 deg cent) but depending on the service life experienced the remnant life gets reduced As a general rule, excess temp over the design temp of 950 deg cent (please do not confuse with operating tempeerature of 910 deg cent) life expectancy gets affected due to "tertiary creep" advancement in reformer tubes. Among the commonly prevailing and practised N.D.T techniques for assessment of creep related damages in reformer tubes, UT two probe send and pick scan of the mid-wall fissures (UT sned and pick up probe design holder - auto crawler scan) is still the most reliable, fast and fairly accurate technique. Confirmatory RT will give a prediction accuracy of 80-90% if the assessing inspection company possesses sound knowledge and expertise to evaulate each tube carefully.%5C A confirmatory surface metallography, radiography of the weld joints will mostly help the assessing inspection company to give more surer way of prediction to grade the severity of tertiary creep damages in steam-naptha reformer tubes. Magnetic permeabiliity - developed orginally in late 1960's and early 1970 by Germany, is not a fool proof method. Magnetica Permeability is a good method for pyrolysis furnace from the point of evaluating the repair capability of a pyrolysis tube. Internal bore view of surface defects- using optical borsocope or video (when reformer catalyst is removed) will give some information but need not necessarily give any prediction capability of the surface internal bore carburization and oxidation that would take place in steam-naphtha reformer tubes. If the inspection agency who did UT auto crawler sender - reciever dual probe scan of your reformer tubes on two successive times in 6 years (with a gap of 3 years) had carefully evaluated andd graded the severity ofthe tubes , prediction result should be close to 80% from severity gradation + the confirmatory RT and surface metallography done on two successive 3 year period in the last 6 years. If you feel the evaluation assessment done may need a second independent survey, you can entrust the job to some other agency using the same prevailing and well accepted practises of UT dual sender -receiver twin probe auto crawler scan+ RT + surface confrimatory metallography to get more surer prediction of the "tertiary creep fissure gradation" in your Paralloy H 39 tubes. If the tubes had been operated at close to 910 deg cent with no excesses, and the results of two successive NDT UT Auto crawler + RT is surer and corroborative in nature, you need not be unduly worried about the remaining life of Paralloy H 39 material for another couple of years. For good assessment and evaluation of remaining life in a reformer tube, one technique is not good enough. Combination of UT twin probe auto crawler + RT + surface metallography + take into consideration the upsets in plant shut down history, operationa dn history of the tubes, catalyst perfomance during the preceding two years (at least), knowledge on high temperature metallurgy for high alloy materials are needed for any inspection company to carefully give a predictable assurance from "tertiary creep related damges" in reformer tubes. Trust this answers your querry. C.V.Srinivasan Nishi Engineers Pvt Ltd India Nov 2,006 E-mail: nishi@vsnl.com. >Hello, >We have a Hydrogen reformer (Steam+Naphtha reformer) of >Paralloy H39 WM Tubes (Dia 4", 12 mm thk, 12.5 m length, 104 >nos.). The Design Temperature specified in the Tubes drawing >is 950 deg C. >Regular Reformer tube skin temperature is monitored by the >plant operating staff using a Optical Pyrometer supplied by >the Process Licensor. A max limit of 910 deg C is specified >for the skin temperature of tubes as per the Operating >manual. Further, the manual also states that 10% of tubes >skin temperature can reach upto a max 950 deg C. >For me there appears some ambiguity in the two max >temperature limits specified. >From a pure metallurgical perspective , what is the max. >skin temperature that can be specifed for the Paralloy H 39 >WM grade tubes? Basically what is the safe limit for the >Operating Staff to be considered during their monitoring? >Also, request for new/latest techniques for carrying out >integrity assessment of the Reformer Tubes during the next >outage. Incidentally we have carried out Automated >Ultrasonic Scanning twice since the Reformer was >commissioned in the year 2000. (an average periodicity of 3 >years) >Regards, >Chakradhar >email: chakradhars@yahoo.co.in