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NDE 2017 Conference & Exhibition of the Indian Society for NDT (ISNT ) 14-16 December 2017,CVhennai ,TN ,India

Residual Life Assessment of Reformer Tubes

Bashisth SINGH Proprietor / Engg. Consultant [QA/QC]:

M/s Premier Inspection & Certification Bureau Navi-Mumbai 400614,Maharashtra ,INDIA

Emai: picbmumbai@gmail.com M] 9892598235/ 7506242436

Abstract Reformer Tubes are Pressure vessels in tubular form, which are subjected to stringent operating conditions namely high pressures [17 to 21 Kg/cm2g ] & high temperatures [8800C to 9800C ]. These conditions demand use of special materials to withstand high temperatures and pressures. The operation is kept ceaseless for prolonged period to achieve maximum rate of reaction between the reactants in presence of catalyst for synthesis of NH3 & Reforming of Hydrogen. This paper discusses about Creep strain as primary cause of Reformer Tube failure amongst all other causes. Under this case of investigation, same set Reformer Tubes were examined and tested annually for seven years in continuation. The results have been presented in this paper.

The Reformer Tubes materials put up in service were HK- 40 [25 nos.] & HP Modified [05 nos.] out of total 30 Tubes. The observations were made in respect of its physical condition, OD measurements [as representative of Circumferential Creep Strain], Bowing of Tubes (as

representative of Axial Creep Strain), Ultrasonic Flaw detection using Through Transmission

Technique [Degree of Energy Attenuation for detection & assessment of internal defects]. The use of HP-Modified material found to increase the Mean Reformer Life owing to its favorable metallurgical properties. The data obtained showed that circumferential creep strain in Reformer Tubes on account of Hoop Stress goes on increasing at much faster pace & led to creation of internal voids as represented by complete loss of Ultrasonic incident energy. The Circumferential Creep strain has been assessed to be more harmful with respect to the Axial Creep Strain.

Key Words: Reformer Tubes, Creep Strain, Through Transmission Technique, Energy Attenuation, Mean Reformer

Life.

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1.0 INTRODUCTION

Reformer tubes are Pressure vessels having large L/D ratio, arranged in large numbers in rows & columns in furnace .These tubes are subjected to severe operating conditions namely high pressures [17 to 21 Bars] & temperatures [8800C to 9800C ]. These conditions demand use of special materials to be able to withstand stringent conditions for reforming reaction to take place. In addition to this, the operation is required to be ceaseless for months together to achieve maximum rate of reaction between the reactants in presence of catalyst for synthesis of Ammonia and reforming of Hydrogen to result higher yield of desired product. The reformer tubes are high Cr, high Ni, Fe alloys and are centrifugally cast to yield preferred metallurgical structure to meet demanding material properties. The continued reaction of reforming under high pressures & high temperatures make reformer tubes prone to failures after certain interval of time. The tubes were examined and tested in respect of its physical condition, tube OD increments (as

representative of Circumferential Creep Strain), bowing measurements (as representative of Longitudinal Creep Strain), Ultrasonic Flaw Detection using Through Transmission Technique for detection of internal defects like voids, cracks, micro-fissures, Hardness tests in vicinity of the weld joints & DP examination of weld Joints for detection of cracks in weld metal, HAZ and parent metal. Inspection and testing of tubes were done year after year in continuation for seven years during scheduled plant shut downs with no change in operating parameters and conditions.

Reformer unit is set up in Fertilizer and Chemical industries wherever the plant activity requires production of Hydrogen gas and Ammonia gas. The Reformer tubes are important constituents of reformer unit. A large number of these tubes are vertically positioned in rows and columns. Creep failure of Reformer Tubes is one of the major issues being faced in Reformer Unit operation.

2.0 REFINING PROCESS IN BRIEF

In steam refining process, a light Hydro carbon Feed stock (such as natural gas, refining gas, LNG or Naptha) is reacted with steam at elevated temperatures (8800 to 9800 C) & pressures (17 to 21 Bars) in nickel based catalyst filled tubes. This gas mainly consists of hydrogen and carbon monoxide but other gases such as CO2, N2, as well as, water vapors are also present. The typical ratio of gas existing in reformer is approximately 50% H2, 10% CO, and balance being other gases.

2.1 The typical Steam to Carbon ratio falls in the range of approx 3:1. The primary reforming reaction is highly endothermic,

CH4 + H2O < - > CO + 3 H2 Dh = + 206.16 kJ/mole of CH4

Since the reaction is endothermic, it requires very high energy input to sustain the ongoing reaction. In order to overcome endothermic reaction, the catalyst filled tubes are heated from the combustion of fuels, such as natural gas, plant gas and PSA purge gas. The production plant includes a steam reforming unit such as primary reformer and a secondary reformer. Ceramic catalysts of different types like Topsoe, R-67 UCI, C-11 etc in different shapes are used with catalyst coating of 12 to 20% Ni on Alumina and spinal supports are used for primary refining.

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2.2 TUBES ARE FED WITH HYDRO CARBON & STEAM MIXTURE

The catalyst synthesizes ammonia by chemically combining hydrogen and nitrogen under pressure. Catalytic reaction of steam & hydro carbon mixture at elevated temperature supplies Hydrogen for reaction.

Cn Hm + nH2O = nCO + [m/2 + n] H2. ----------------- 1

CO + H2O = CO2 + H2 ---------------- 2

Since the number of moles of product exceeds the number of moles of reactants, this is an endothermic reaction and requires energy input from external source [by burning natural gas or naptha] in order to sustain the reaction.

3.0 REFORMER TUBE MATERIALS & PROPERTIES

The commonly used Reformer Tube materials are HK-40, HP Modified & Micro- alloy material

[Nb Stabilized]. These are special high strength alloy steels which are resistant to high creep, resistant to high temperature and resistant to oxidation of reformer tube material with furnace contaminants. The Niobium stabilized alloys have an advantage over commonly used materials in steam Hydro carbon refining. Such reaction requires special materials that have high creep strength and still meets the service conditions. The Reformer Tubes are made of basically Cr - Ni Steels. Under the severe operating conditions, the reformer tubes start creep and rupture after prolonged interval of time. The major factors for tube deformations are high internal pressures and tube wall temperatures.

a) Material HK- 40 : 25% Cr, 20% Ni Steel b) HP 50 - Modified : 35% Cr, 25% Ni + 1.5% Niobium c) Other materials are : Micro alloys 35% Cr, 25% Ni + other elements. d) IN 519 : 24% Cr, 24% Ni + Nb

The reaction in reformer is endothermic and proceeds with increase in volume. However, the tube material limits the allowable increase in temperature. The material HK 40 is being used for years. Now-a-days HP-Modified is being used with 1.5%

Nb due to its improved temperature properties. HP-Modified is being used for reforming pressure of 40 bars @ tube wall temperatures of 9000C. Commonly used for replacements and new Plants. Use of micro alloys Ti & Zr are another improvement. These micro alloys, permits, the use of low thickness tubes while maintaining the same tube life of 100000 hrs or even more . By installing the tubes with lesser wall thickness and / or wider diameters the capacity of the front end of the NH3 plant can be increased significantly.

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The use of micro alloyed reformer tubes with minimum wall thickness can increase the catalyst volume, increase the firing temperature and lower pressure drop. The reformer tubes [high Cr, high Ni ,Fe alloys], austenitic in phase and are centrifugally cast to yield preferred metallurgical structure to meet the demanding material properties though the chemistry & metallurgy of reformer tube materials are adjusted to make them resistant to creep strain, resistant to high temperatures and resistant to oxide formation on the external surfaces of tubes with contaminants in furnace atmosphere, the continued reaction of reforming under high pressures and temperatures make reformer tubes prone to failures after certain interval of time.

3.1 TYPE & SIZE OF REFORMER TUBES UNDER OUR RLA STUDY

The tube materials : HK-40 (25 nos.) & HP-Modified (05 nos.). Total 30 Tubes. Tube dimensions : 10000 mm (L)x O/D 202 mm x Wall thickness 11 mm, I/D 182 mm . The Reformer Tubes are centrifugally cast to obtain favorable metallurgical structure, to enhance temperature resistance, Creep resistance at high temperature & High resistance to deformation.

Fig. Representation of Reformer Tubes in Rows & Columns

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3.2 REFORMER TUBE SET UP

The reformer tubes are positioned vertically. The topside of tubes is welded with reducers & flanges, connected with inlet lines. The bottom side is connected with Header and Pig tails, out let lines for the product.

Fig. 3 : Schematic Diagram of Reformer Tube representing inlet /out let lines & Catalyst inside

4 .0 MEAN LIFE OF REFORMER TUBES & OPERATIONAL FACTORS

Mean Life of reformer tube is 100000 Hrs (One lakh Hour). The lost time for reformer operation per year is almost two months i.e. 60 days to 65 days. One month (30 to 35 days) is required for complete overhaul and attending all trouble shooting areas and one month (30 days) required for intermittent shut downs of shorter periods for attending general maintenance jobs. Keeping aside this down time, the unit operates on an average for 10 months (300 days approx) only in an year (effective number of actual working days / yr).

The total number of hours of reformer unit operation is limited to 7200 hours per year. With this level of operation, Reformer Life achieved is approx 14 years using normal grade reformer tube material (HK-40). In some cases saving is done through proper maintenance work and sound engineering practices and able to save an additional 15 days in a year out against total down time of 65 days of per year. This in turn, results in increase in efficiency of 210 days working days in 14 years of service, this may be considered equivalent to a year. Taking all these operational factors into account the reformer tube is assumed to have maximum life span of 15 years with best possible up keep of reformer unit. Through use of modified grade material, the mean life of reformer unit achievable is up to 18 years or more which results in to gain of 20 % against normal grade material.

Key Points in Reformer Operation:

i) Runs continuously for : 24 hours ii) Healthy reformer unit runs for min. no of days/year : 300 days iii) Minimum no. of hours of run for reformer unit : 300 x 24 = 7200 hours/ year iv) Max no. of hours run of reformer unit / year : 315 x 24 = 7560 hours/ year

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[with improved maintenance, reducing down period time ]

v) Average running hours for reformer unit : 7380 hrs. per year vi) Maximum reformer run hours /year under

best possible conditions of reformer operation : 7500 hours/year

vii) Minimum reformer run hours/year [taking in to account various hurdles & MNT problems] : 7000 hours/year

Note: For all calculations & evaluation of residual life of reformer tubes, run of approximate 7200 hours/year is taken into account.

4.1 TECHNIQUE FOR INCREASING MEAN LIFE OF REFORMER TUBES

4.1.1 With the use of Modified Grade an increase in reformer tube life is possible to the extent of 20000 hrs additional operation time. This works out to the tune of minimum additional working period of 2.86 years (approx 3.0 years). 4.1.2 By reducing operating temperature and pressure of reformer tubes and ensuring that the temperature distribution is uniform throughout the furnace. The temperature gradient must be kept between 500C. 4.1.3 Carrying out periodic checks of reformer unit components inclusive of tubes, headers, firing nozzles, maintaining proper refractory bricks condition of furnace, appearance of hot spots, avoiding temperature shoot outs during operation.

4.2 TECHNIQUE FOR INCREASING EFFICIENCY OF REFORMER TUBES

4.2.1 By increasing internal diameter of tubes and reducing its wall thickness by using improved grades of reformer materials. Through the use of micro alloys & HP modified material, it is possible to use tubes of relatively lower wall thickness, thereby increasing internal volume in reformer tube for containing increased quantity of catalyst inside the tubes. 4.2.2 Efficiency can also be increased by operating reformer unit at higher temperature & higher internal pressure. It is observed that reformer tubes have been designed to operate at pressure of 30 to 35 bars and temperature of 9200C to 9800C. However, the risk of failures increases under these limiting conditions.

5.0 SPECIAL FEATURES CONCERNING RLA STUDY OF REFORMER TUBES

Reformer tubes inspected mainly in three chemical companies as detailed a) M/s HOC Ltd. Rasayani, Maharashtra (H2 Phase -I, Phase -II & Phase -III Plants). b) M/s Deepak Fertilizers & Petrochemicals Corporation Ltd. MIDC Taloja -Ammonia Plant c) M/s Rama Petro ChemicalsLtd. Patalganga ,MIDC, Raigad, Maharashtra.-Ammonia Plant

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6.0 DEFECTS ENCOUNTERED AND THEIR CAUSES

6.1. BOWING IN REFORMER TUBES, CAUSES & REMEDIES

The reformer tubes remain in almost straight condition up to 55000 hrs to 60000 hrs of running (8 years+). After 8 years of service aging in tubes starts & bowing in tubes gets visual. The top and bottom ends of reformer tubes are connected to other components in reformer unit and they are rigid bodies. On these counts, the tubes experience constraints in regards to their axial expansion. The longitudinal creep strain sets in reformer tubes in form of axial creep strain. Since the two ends are almost rigidly fixed, the tubes have no room left to take care of increments in length in axial direction, thereby giving way for deformation of tubes in horizontal direction rather than vertical. The pattern of bowing in tubes is non uniform and takes place in

random directions at any level and to any degree. Bowing in reformer tubes found to occur as

much as up to 125 to 150 mm.

Fig-3 Reformer Tubes Original condition Fig: 4 Reformer Tubes condition @ 110000 hrs 6.2 HOT SPOTS IN REFORMER TUBES

Reddish color patch marks on external surfaces of tubes are generally noticed in regions of high firing zone on account of exposure of tube to high temperature. These marks appear as round spots in sizes 25 mm to 40 mm diameter. These are indicative of localized excessive oxidation of tubes on its external surface.

6.3 POINT OF INFLEXION IN TUBES

This type of defects are noted in rare cases, however these defects are quite vulnerable. Point of inflexion type of defects in tubes occur in upper segment of tube just below the top roof of furnace and limited in a small zone within 300 to 500 mm length. The tube gets deformed in such a way that it takes shape of a curve like point of inflexion (sharp U-turn with both upward and down ward deformation) due to increment in length and no scope for further upward movement. The tube at high temperature & pressure with heavy degree of restriction deflects it from its original vertical axis and takes sharp U-Turn with inverted U. This reflects sudden heavy plastic deformation of tube owing to excessive axial stress. Since the tube materials are very hard and brittle, the creation of defect shows cracks at outer bent regions of both upper and lower U-bends of the tube (Ref.Fig.4).

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6.4 LOCALIZED BULGING & OXIDATION DAMAGE IN TUBES

Tubes start showing bulging in tubes after it has undergone service of 10 to 12years i.e. 77000 to 85000 hours of run in the furnace. These defects occur at few locations where heat input received through firing nozzles directly impinging on tube wall surface. These defects are visible under close visual examination. Light to heavy oxidation on external surfaces also noted in tubes adjacent to high heat input areas. The basic cause is due to high thermal gradient in a limited zone & when operation is done under high internal pressure as well. The tube bulging is often accompanied with tube twisting and appearance of hot spots. 7.0 CREEP PHENOMENA IN REFORMER TUBES

Creep is defined as a time-dependent deformation at elevated temperature and constant stress. The failure from such a condition is referred to as a creep failure or, occasionally, a stress rupture. The temperature at which creep begins depends on alloy composition. The conditions in reformer tubes are such that creep in material cannot be avoided. It has to be contained and controlled to enhance the working life of reformer Tubes.

Fig : Deformation of material with time [ Representation of Stages of Creep ]

7.1 COST OF REPLACEMNET OF REFORMER TUBES

The replacement of the reformer tubes is a very costly affair. According to data obtained from Fertilizers Corporation of India as per the cost estimates reformer unit requires an investment of $50 million to 60 million with payback time of minimum 40 to 48 months. Keeping this cost factor in mind it is always desired to use to tubes to their fullest life period. As a thumb rule the mean life of reformer tubes are estimated to be one lac hour (100,000 Hrs) by the use of improved grade of material, it has become now possible to enhance the life by 15000 to 20000 hrs additionally.

7.2 CREEP FAILURES IN REFORMER TUBES Creep failure in reformer tubes is the primary cause among all failures. Basically two types of creep occur in reformer tubes. Creep failures are characterized by: increments in OD, by appearance of Bulging /Hot-Spots/Blisters, thick-edged fractures often with very little ductility and longitudinal "stress cracks" in tubes either on ID or OD, oxide scales on external/internal, surfaces and mid wall cracking in tubes.

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7.2.1 LONGITUDINAL CREEP IN TUBES

The high temperature causes axial stress in body of tube leading to longitudinal creep, which gets reflected in form of bowing of tubes, once top & bottom ends of tubes get restricted. In physical form, this longitudinal creep in tubes is reflected in form of Bowing of Tubes after prolonged working hours. This creep also leads to longitudinal stress cracks.

7.2.2 CIRCUMFERENTIAL CREEP IN TUBES

High pressures in tube create Hoop Stress, there by developing circumferential creep. This creep results in form of increased OD of reformer rubes after large number of working hours. The visible change in diameter of tubes is noticed only after 10 years of reformer operation. High temperatures and high pressures in reformer rubes generate huge internal stresses, one in form of longitudinal stress and the other in form of circumferential stress, this results is in form of Longitudinal Creep strain & Circumferential creep strain. These two types of strains are the main causes for reducing the life of reformer tubes. The longitudinal creep strain is acceptable to a great extent so far as direct damage to reformer tubes is concerned. However the circumferential creep strain is not acceptable due to the fact that increase in diameter of tubes results in creation of internal voids in the tube material, particularly in the mid wall region. In this case the term true OD has been used for evaluation purposes. True OD of tube refers to an imaginary circumferential line diameter of tube mid wall. For assessment of Reformer tube material degradation, True OD value is taken into consideration because the mid wall tube material experiences an average temperature and pressure. The mid wall of tube is the true representative of being exposed to actual temperature and pressure conditions prevailing in the tubes.

Table No 1 Increments in OD of Reformer Tubes (Creep measurements in terms of Tube Dia) Reformer Tube mid wall diameter: 193 mm (True OD) Creep data of tubes from 10th yr up to 16th yr [Original OD of Tubes: 202 mm]

Running Year

Reformer Run hrs

Measured OD [ mm]

Aveg. OD

Increment in OD

% increase in OD (% CREEP)

% Creep w.r.t

mid wall line dia True OD of 193 mm

Remarks

10th Yr 72000 202.15 202.68

202.42 0.42 0.848 0.810 From 14th year onwards i.e after 95000 hrs of run the growth rate of creep in the Reformer tubes is very fast .This indicates the fast aging of reformer tubes

11th Yr 78500 202.60 202.90

202.75 0.75 1.515 1.450

12th Yr 86000 202.70 203.40

203.05 1.05 2.121 2.026

13th Yr 92500 • Complete test could not be performed owing to some process

constraints and time limitations

14th Yr 98000 203.10 203.96

203.53 1.53 3.090 2.953

15th Yr 105000 203.82 204.58

204.20 2.20 4.444 4.246

16th Yr

112000 204..16 205.46

204.81 2.81 5.676 5.423

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7.2.3 CREEP TEST RESULT & SIZING OF INTERNAL DEFECTS

As precise evaluation and sizing of internal defects is not possible in reformer tube materials owing to its rough surfaces, uneven surface contours, and high degree of energy attenuation accompanied with simultaneous bowing and existence of ovality in reformer tubes the estimation of internal defects generated in the tubes are primarily judged on the basis of circumferential creep strain at its mid wall line diameter (referred to as True OD of Tube) as direct representation of internal voids. Under the prevailing operating conditions of reformer tubes, the mid wall region is considered to be the true representative of reformer tubes metallurgical conditions. The creep test results analyzed in respect of true OD of reformer Tubes under RLA study. Out of total 30 tubes, 14 tubes exhibited creep exceeding 5% value. An increase of 5% at mid wall line diameter of 193 mm accounts for 2.81 mm increment which is equivalent to an increase in circumference length at mid wall location to the order of 8.83 mm. Assuming that 50% of this increment is consumed for plastic deformation, the remaining 50% goes for directly creating the voids, cracks/micro cracks to the order of 4.41 mm total cumulative length of internal defects. This figure can be taken as turning in to void formation. Assuming as if 4.41 mm incremental length in circumference at mid wall line, if located at random locations at 20 spots along the periphery separately, individual void size is 0.22 mm i.e. 220 microns. The size of voids / cracks at mid wall location of tube is enough to degrade the reformer tube material prone to the stage of failure. On the basis of this test result it was suggested to replace all the 14 tubes showing creep exceeding 5%. Almost 50 % of tubes reached the stage of abandonment.

8.0 METALLURGICAL FAILURES

8.1 OXIDE FORMATION ON INTERNAL & EXTERNAL SURFACES OF TUBES

Fig-1 Oxidation -1st Stage Fig-2 Oxidation -2nd Stage

Fig.3 Microstructure shows voids/micro crack Fig. Initiation of voids

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9.0 ULTRASONIC FLAW DETECTION OF REFORMER TUBES [ UFD

9.1 OBJECTIVE AND TECHNIQUE USED The actual condition monitoring of reformer tubes is done through Ultrasonic Flaw detection of tube material using THROUGH TRANSMISSION TECHNIQUE . The damage done due to high degree of Circumferential Creep Strain is assessed through this technique as it evaluates the kind of internal damage done in tube material .The loss of ultrasonic energy while passing through it represents the presence of internal cavities, voids, micro-cracks, porous character & micro fissures.

9.2 PARAMETER AND TEST RESULTS : Table No 1 A (Test Parameters)

Ultrasonic Flaw detection using through Transmission technique

Probes used - 2 Nos 1] Transmitter & 2] Receiver

Probe Size & Type

25 mm dia -Normal Beam Probes Frequency

2.5 MHz

Scanning

100 % with 15 % overlap. Type of Transmission

Through Transmission Mode of scanning

Manual [ ½ x ½ Circum ]

Ref, Attenuation Level 56 dB Actual Scanning Level 68 dB Couplant : D.M.Water

Type of scanning : Manual At a time half circumference and vertical movement 1500 mm

The schematic arrangement for Through Transmission is shown in Fig – No 3

9.3 LOSS OF ENERGY DURING TRANSIT THROUGH TUBE : The table below indicates the degree of loss of ultrasonic energy while passing through the body

of tube materials . 10th Year 11th year 12th year 14th year 15th year 16th year

Hours of Service

72000 78500 86000 98000 105000 112000

Energy loss for 10th year Ref. Level.

40% loss in 25 % Tube of of x-sectional area

50 to 55 % loss in 40 % x-sectional area

60 to 65 %

loss in 50 % x-sectional area

70 to 80 % loss in 60 % x-sectional area

80 to 90 %

60 % of x-sectional area

90to 100% in

70 % Tube x-sectional area

Energy loss in terms of Attenuation

Reference Scanning dB - 68

72 to 74 dB 78 - 80 dB 86-90 dB

94- 102

dB

No signal at the receiving end All transmitted energy getting lost.

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9.4 ANALYSIS OF ULRASONIC FLAW TEST RESULT:

Ultrasonic energy loss [Attenuation of ultrasonic energy] during transit through reformer tube material is of very high order. Up to 10 years of service, reformer tubes are young. As the time passes by, the aging rate in tubes enhances at faster rate day by day and year by year. From 12th year onwards close examination and health monitoring of reformer unit becomes essential. The heavy loss of energy is indicates that the tube material has developed voids micro- fissures in the mid wall region and absorbs transmitted ultrasonic energy to a great extent. The pattern of the energy loss at the receiving end gives signal about the deteriorating condition of tubes in respect of its soundness. It also indicates that the material is getting porous inside slowly but certainly. The complete loss of energy shows that the tube material has turned into an unsound state and needs its replacement. 10.0 CONCLUSIONS

As a result of visual examination, NDT tests and creep measurements of reformer tubes it was concluded that up to 72000 hours of running, using HK 40 material did not show any visible defect in regards to its creep & tube bowing .Creep in tubes up to 10 years service limited to the order of 0.81 % .With subsequent years after 11th year & 12th year creep values found to increase .Up to 12th year creep was limited to 2.0 % . The results show that at 14th year creep found to the order of 2.953 % i.e. almost 3.0 % and this value crossed 4.0 % and then 5.0 % at the end of 15th & 16th year respectively indicating very fast deterioration of reformer tubes in terms of developing creep strain. Significant loss of incident energy under ultrasonic testing using through transmission technique observed, indicating nucleation and formation of internal micro cracks micro- fissures and voids. The tubes in initial years of operation up to 10 years the attenuation in reformer tubes was at a normal level as expected for cast materials. However with passage of time and increased years of operations, particularly after 90000 years of reformer service the energy attenuations found to be of alarming proportions. At the age of 16 years i.e. 112000 hrs, more that 50 % of reformer tube cross sectional areas revealed total loss of the incident energy as shown above in the corresponding table. The reformer tubes show excessive bowing, these get de-shaped after 14 years of operation. Tube bowing noted to the order of 125 mm. These are bent so much that they start touching each other. To summarize the results in brief, it may be safely concluded that for reformer tube material of Gr.HK-40, safe run is possible up to 90000 hrs of service. With increased hours of operation in the subsequent years, extreme caution is required to be exercised for its proper evaluation of creep strain, tube bowing and ultrasonic tests for attenuation results. Close control of operational factors and thorough external examination required is to be performed on an annual basis. The test results of reformer tubes using HK-40 grade material with 112000 hrs [16 years] of operation revealed that the condition of almost 50% tubes is un- satisfactory and they had to be abandoned against use in service to avoid failure during operation and causing any mishap.

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10. REFERENCES

1. ASM Metals handbook Vol.11 , failure investigations

2. Experience of repeated NDT Testing , inspection and evaluation of reformer tubes in various chemical / petrochemical companie. 3. NDT in predicting of processing furnace remaining life, NDT for Safety 2007, Prague, Czech Republic 4. A comprehensive approach to Insp.& Assessment of H2 reformer tubes, API Insp. Subcommittee, IESCO 5. Integrity and life assessment of catalytic reformer units, John Brear & John Williamson

6. Reformer furnaces: materials, damage mechanisms & assessment by Tito Luiz da Silveira & Iain

Lemay

7. R.Singh “Metallurgy &Weldability of Steam Hydrocarbon reforming equip.,thesis paper TWI-2000

8. S R Keown, FB Pickering ‘Effect of Niobium carbide on the creep rupture properties of Austenitic steels“ASM Handbook Service conditions in the chemical industry[Materials Park OH,ASM ] 9. B.M. Patchett, R.W. Skwarok, “Welding and Metallurgy of 20Cr-32Ni-Nb and HP 45 Castings,” Proc. of Conference by the Metallurgical Society of CIM, 1998. 10. A.Chitty, D. Duval, “Creep Rupture Properties of Tubes for High Temperature Steam Power Plants,” Proc. of Joint International Conference on Creep, The Institute of Mechanical Engineers, London,1963. 11. Evaluation of reformer tube degradation after long term operation. By J Kabanowski Gadarisk Univ. of Technology Poland