CnW Maintenance Manual 505-518 PDF

APPENDIX-VI-GUIDELINES FOR MAINTENANCE & Page 1 of 14 REPAIR OF STAINLESS STEEL WAGONS APPENDIX “VI” GUIDELINES FOR MAINTENANCE & REPAIR...

APPENDIX-VI-GUIDELINES FOR MAINTENANCE & Page 1 of 14 REPAIR OF STAINLESS STEEL WAGONS APPENDIX “VI” GUIDELINES FOR MAINTENANCE & REPAIR OF STAINLESS STEEL WAGONS APPENDIX-VI-GUIDELINES FOR MAINTENANCE & Page 2 of 14 REPAIR OF STAINLESS STEEL WAGONS GUIDELINES FOR MAINTENANCE & REPAIR OF STAINLESS STEEL WAGONS CONTENTS 1. Introduction-:................................................................................................................. 3 2. Stainless Steel : The peculiarities:................................................................................. 3 3. Maintenance of SS Wagons : An Overview................................................................... 4 4. Facilities required for maintenance of Stainless steel Wagons:-................................ 4 5. MAINTENANCE ACTIVITIES IN SS WAGONS.................................................... 5 5.1 Inspection 5.2 Cutting 5.3 Straightening 5.4 Replacement 5.5 Welding 6. SURFACE PREPARATION & PAINTING............................................................. 13 WAGON MAINTENANCE MANUAL APPENDIX-VI-GUIDELINES FOR MAINTENANCE & Page 3 of 14 REPAIR OF STAINLESS STEEL WAGONS 1. INTRODUCTION-: Corrosion is perhaps, the single biggest challenge that needs to be surmounted, to attain increased service life of Wagons. Continuous exposure to moisture, air & high temperature, repair practices resulting in localized heating, loading/ unloading practices resulting in damages to the employed surface protection& incorrect/ inadequate surface protection are the main causes of propagation of corrosion. An effective means of tackling corrosion is by selecting corrosion-resistant raw material for fabrication of wagons. Such a selection, however, has, to consider, weldability, ease of fabrication, formability & availability of the chosen raw material besides the cost. Based on the above considerations, IR has introduced the use of Ferritic grade Stainless Steel (SS), to IRSM:44 specification, in BOXNHL & BCNHL wagons. Based on the experiences gained, IRSM:44, has also been introduced in rehab of BOXN wagons- BOXNR wagons. The introduction of SS, has brought forth maintenance issues, related to cutting, welding or straightening of SS, patch repairs, attention to various types of similar and dissimilar joints between stainless steel, carbon steel and corten steel. To understand, these maintenance issues, it is important to understand the inherent properties of SS & how it is different than the conventional MS, used hither-to in wagon fabrication. 2. STAINLESS STEEL: THE PECULIARITIES: The chemistry of Stainless steel differs from carbon steel by the amount of chromium present. The presence of Cr, promotes the development of an invisible, adherent and self-healing chromium-rich oxide surface film. Carbon steel rusts when exposed to air and moisture. This rust, essentially an iron oxide film is active and accelerates corrosion by forming more iron oxide. Stainless steels have sufficient amount of chromium present so that a passive film of chromium oxide forms on initial oxidation, which prevents further corrosion. The tough chromium-oxide layer, also comes into play, during the repair/ cutting of SS. In conventional carbon steels, during, oxy-cutting the metal is first heated by the flame, and then an excess of oxygen is supplied. This causes an exothermic (heat generation) reaction which generates the heat necessary to melt the oxides formed, which are then removed from the cut by the velocity of the gas jet. In this process a rough surface is produced. Where as, stainless steels having a high level of Chromium (Cr) cannot be cut by simple oxy-cutting methods due to the refractory nature (very high melting point) of the Chrome Oxide which is formed as the top layer. Ferritic stainless steels are generally limited to service temperatures below 750°F (400°C) due to the formation of embrittling phases, which may also precipitate during welding. Primary concerns with welding ferritic grades are maintaining adequate toughness and ductility in the as-welded condition. WAGON MAINTENANCE MANUAL APPENDIX-VI-GUIDELINES FOR MAINTENANCE & Page 4 of 14 REPAIR OF STAINLESS STEEL WAGONS 3. MAINTENANCE OF SS WAGONS: AN OVERVIEW RDSO has introduced SS in the newly designed BOXNHL, BOXNLW, BOXNR & BCNHL wagons. In constructional design, BOXNHL, BOXNR and BOXNLW wagon are similar to BOXN wagon and BCNHL wagon is similar to BCNA wagon. Hence, the maintenance and Repair procedure of these wagons shall be similar to BOXN/BCNA wagons. The procedure for attending to repairs in BOXN & BCNA are given in the Maintenance manual for Wagons Issued by CAMTECH. However, since the wagon body and under frame of BOXNHL, BOXNLW, BOXNR & BCNHL wagons are made of higher grade steel i.e. IRSM-44 /IRS M-41 steel/CRF sections, the cutting, straightening, welding / repairing procedures are slightly different than plain carbon steel wagons. Before elaborating on repair details, it is important to understand that the SS wagon structural members, body panels& other components that form part of the wagon structure, when corroded/damaged, should necessarily be repaired or replaced with similar grade of steel only. 4. FACILITIES REQUIRED FOR MAINTENANCE OF STAINLESS STEEL WAGONS:- Reiterated below, for guidance, are recommended facilities (by CAMTECH) for effective maintenance of SS wagons: S.No. Item/Description Freight Yard Sick line ROH Depot./workshops (maintaining 3 (5 wagon/day) rakes/day) (200 wagons/month) 1. MIG/MAG Welding sets 02 Nos. 02 Nos. 03 Nos. (400 Amp.) 2. DC Arc Welding 02 Nos. 02 Nos. 03 Nos. Rectifier (600 Amp.) 3. Portable Air plasma 02 Nos. 02 Nos. 03 Nos. cutting machine (Max. capacity 16 mm) 4. Consumables for Air As per Requirement Plasma M/C i.e. Torch tip, catalyst etc. 5. Welding electrodes For IRS M-44 to IRS M- As per Requirement 41 etc. WAGON MAINTENANCE MANUAL APPENDIX-VI-GUIDELINES FOR MAINTENANCE & Page 5 of 14 REPAIR OF STAINLESS STEEL WAGONS 6. Lock bolts of various As per Requirement sizes ( 3/8” to 7/8”) 7. Lock bolting Equipment 02 sets 02 sets 03 sets. 8. Portable grinding 03 03 05 Machine (only dedicated grinding wheels & disc should be used.) 9. Stainless steel wire As per Requirement brushes 10 IRS M44 & IRS M41 plates/sheets & CRF sections as per wagon As per Requirement design drawing. Note: The class of welding electrodes for different combinations of materials shall be as per RDSO specification No. G-72 latest revision. 5. MAINTENANCE ACTIVITIES IN SS WAGONS. The maintenance of wagons mainly consist of the activities of Inspection, cutting, straightening, replacement, welding and finally painting. Brief details of these activities, with particular attention to be given for SS wagons, are enumerated below: 5.1 Inspection of Under frame and Body The under frame members & body should be thoroughly inspected for locating cracks, bent/damaged, corroded members. A component that warrants repair should be repaired as per the defined procedure, in the wagon maintenance manual. In case a component/ sub- assembly/ structure is found to be corroded & is judged to be beyond repair, the same should be replaced. Essentially, the repair/ replacement should be done on condition basis. During Inspection of wagons, special/ particular attention should be paid to the below detailed vulnerable members and locations:  Sole bar, side wall stanchions, and floor plates.  Head stock, corner angle and end stanchions.  Top copings, and corner joints.  Door locking brackets and hinges.  Puncturing/damages of side/end sheets.  Centre pivots, and center sill. WAGON MAINTENANCE MANUAL APPENDIX-VI-GUIDELINES FOR MAINTENANCE & Page 6 of 14 REPAIR OF STAINLESS STEEL WAGONS  Cracks in center sill, sole bar and cross members etc.  Breakage/Failure of lock bolts. 5.2 Cutting of IRSM-44: The IRSM-44 steel panels/plates/CRF sections shall be cut either by shearing machine or by plasma cutting machine but not by oxy-cutting. The guidelines for cutting of IRS M-44 are subdivided into the following sections:- a. Guillotining i) The guillotine is normally used for cutting steel up to 16 mm thick. The maximum capacity of the guillotine (used for mild steel shearing) should be downgraded by 30-40% for cutting IRS:M44 because of IRS:M44’s greater shear strength, e.g. if maximum shear capacity is 16mm(mild steel) then the maximum shearing capacity will be 11mm for IRS:M44. ii) “Shear breaks” on the cut edge can be prevented by using well sharpened, correctly aligned and set blades especially for plates heavier than 8mm. iii) Burnish and burr heights increase with increasing blade dullness and blade gap and rollover tends to be excessive. This needs to be taken note of & suitable corrective/ preventive action taken. iv) Shear break or splitting should not be confused with laminations as the former is a result of the shearing process parameters, while the latter is a material defect. Shear break is caused by excessive cutting speeds, blade clearance etc. The following guillotine clearance settings are given for guidance:- Plate Thickness (mm) 3 6 10 Clearance Settings (mm) 0.1 0.15 0.25 v) The most suitable shear blades for cutting IRS:M44 and stainless steel are made of high carbon-high chromium tool steel. The blades must be kept sharp- a good test is to cut a piece of paper. vi) Good practice is to wipe the blade and hold down pads free of adherent mild steel particles prior to cutting IRS:M44. This will avoid mild steel contamination. vii) Where possible, shearing speeds should be reduced by up to 20%. This will prevent shear break of thick plates. b. Plasma cutting Due to high chromium content of IRS:M44 it cannot be cut with the conventional oxy- acetylene torch. Portable plasma cutting equipment with inbuilt liquid tank are also available which can be used for repair work. WAGON MAINTENANCE MANUAL APPENDIX-VI-GUIDELINES FOR MAINTENANCE & Page 7 of 14 REPAIR OF STAINLESS STEEL WAGONS i) Plasma cutting and profiling of IRS:M44 is the fastest and most economic thermal cutting method available. Fast cutting speeds together with a clean smooth surface finish can be achieved. Due to the fast cutting speeds, the heat affected zone is very narrow, minimizing the effect on the properties of the material. Thin plates can be stack-cut. Any discoloration of the cut edge can easily be removed by grinding or by using a stainless steel wire brush. If no subsequent welding is undertaken, edge discoloration must be removed, followed by passivation. ii) Cutting Gases At present, there are many makes of portable plasma cutting machines which are able to cut up to 16mm thick plate. These portable units make use of compressed air (300 – 500 KPa) rather than mixed plasma gases. These machines are light, (weighing not more than an oxy-acetylene set) economical and efficient. Consumable items are the torch tip and the catalyst. For gauges in excess of 16mm, heavier mixed gas plasma cutting machines will have to be used. Oxygen – free nitrogen is the most economical cutting gas. Other gases which can be used include mixtures of argon and hydrogen or nitrogen and hydrogen. The secondary shielding gas can be one of numerous gases such as welding grade carbon dioxide which is inexpensive. Argon or argon-hydrogen mixtures are often used where a better, cleaner cut is required. c. Abrasive Cut – off Wheels Abrasive disc cutting can be used for limited lengths of cut. Only dedicated discs should be used and suitable control of the storage of these must be exercised. Use can be made of water soluble oil for cooling/lubrication. Aluminum oxide discs of the vitrified or resinoid bonded types are suitable. Zirconia silicon carbide discs are not recommended. d. Arc-Air Gouging Arc-Air gouging is a suitable method of cutting provided the recommended settings are adhered to in order to produce acceptable cuts. All cut edges must be ground back (using dedicated grinding discs) to a depth of approximately 2mm to remove the heat affected zone before further fabrication. Areas not subsequently welded must be de- scaled and passivated. e. Powder Cutting Ferrite powder injected into an oxy-acetylene flame can be used to cut IRS:M44, but the unsightly edges produced must be ground back approximately 2-4 mm using dedicated discs before further fabrication, to ensure that the plane edge is of an acceptable quality. Areas not subsequently welded must be de-scaled and passivated. WAGON MAINTENANCE MANUAL APPENDIX-VI-GUIDELINES FOR MAINTENANCE & Page 8 of 14 REPAIR OF STAINLESS STEEL WAGONS f. Slitting After cutting on conventional slitting equipment, edge must be deburred. Slitting knives should be cleaned of all mild steel or other metal contamination before IRS:M44 is processed. Close control of blade clearance will ensure good edges. Blade clearances are as for guillotine settings. g. Cold Sawing Cold sawing is suitable provided a high feed rate is maintained to produce an acceptable cut. Cutting and cooling fluids (water soluble oil type) should be used for cutting thicker gauges. High speed wavy tooth blades are recommended with up to 13 teeth/cm for light gauge material. The number of teeth per centimeter should be reduced as the gauge increases. h. Blanking and Punching These operations can be successfully carried out provided that tools and equipment used have sufficient strength and rigidity to account for the higher proof strength of IRS:M44. Clearance between the punch and the die is normally held to 5% of the metal thickness on a side i.e. 10% overall. Punches must be kept sharp, and where possible, the speed of operation should be reduced. i. Drilling High speed drills should be used on IRS:M44. It is advisable to have the web of the drill thinned as much as possible (up to 1/8 the drilling diameter) to eliminate excessive drilling temperatures caused by the friction generated at the bottom of the hole. The included angle of the cutting edge should be ± 120°. The drills should be as short as possible to improve rigidity. A suitable cutting compound (sulphurized or chlorinated oil) should be used for drilling deep holes. Cooling of the drill cutting edge can be effected using a light water-soluble oil which will extend drill life. Drills should be backed out at regular intervals to relieve chip congestion. 5.3 Straightening of IRSM-44: The wagon members which are bent/deformed can be straightened up to a certain extent. It is notable that IRS:M44requires, greater bending capacity to straighten the steel members owing to its higher yield strength. As an approximation, the maximum capacity of the bending is reduced by 40% for bending IRS:M44 compared to mild steel. Also, IRS:M44 generally exhibits greater spring back than mild steel during bending. This should, hence, be compensated for, by slight over-bending, e.g. 5% on a 900 bend. Use of hydraulically/ manually operated Tie screw pulling and hammering is recommended for bending /straightening wagon members. The members which are more than 5mm thick and are distorted/bend can be heated locally upto 1500C and straightened by hammering/pulling. However, heating of stainless steel members beyond 1500C should be avoided in view of change in chemistry of steel. WAGON MAINTENANCE MANUAL APPENDIX-VI-GUIDELINES FOR MAINTENANCE & Page 9 of 14 REPAIR OF STAINLESS STEEL WAGONS If members are badly distorted/bent and straightening is not possible, the members should be replaced with similar grade of materials, instead of attempting major repairs by heating/ straightening. It is also recommended that in case severe bending of thicker plate sections, needs to be done, such bending operations should be carried out before welding operations, so as to avoid the possibility of heat affected zone cracking. Edge cracks can be avoided by placing the cut face on the outside radius of the bend and the sheared face on the inside. This type of cracking can also be prevented by grinding the outside radius point of bending into a rounded profile. Thus, eliminating the natural stress concentration point. 5.4 Replacement Heavily damaged members should be replaced with similar grade of steel with new members. 5.5 Welding Procedure:- The main differences between welding stainless steel and mild steel are owing to differences in properties of SS in terms of coefficient of linear expansion, thermal conductivity, ductility etc. This affects the work hardening and shock absorption properties. For stainless steel welding various welding processes can be used such as MIG, TIG, MMAW, Resistance welding and laser welding. However, the following issues, need to be considered in case of SS repairs: 5.5.1 General Precautions in Welding of Stainless Steel i. Since Stainless steel has high coefficient of thermal expansion and less heat conductivity, it is advised to use low welding currents in the recommended range and smaller gauge electrode to minimize heat input and reduce distortions. ii. Surface to be welded must be clean, dry and free from dirt, oxide film, oil, grease, paints etc. iii. Electrodes should be re-dried before use. iv. Always maintain short arc to minimize the loss of alloying elements. v. Avoid weaving and make stringer beads. vi. After finishing welding, lift electrode slowly and fill the crater before breaking the arc. This will avoid crater cracks. vii. Use stainless steel wire brush for cleaning welds. viii. Use electrode preferably with DC (+). WAGON MAINTENANCE MANUAL APPENDIX-VI-GUIDELINES FOR MAINTENANCE & Page 10 of 14 REPAIR OF STAINLESS STEEL WAGONS ix. Every bead should be properly cleaned before further welding on it. x. Welding should be preferably carried out in flat position. xi. Correct electrode size, recommended current, arc length, travel speed and electrode angle must be followed. xii. Any defect like crack, blowhole etc. must be properly gouged out and re- welded. xiii. Do not strike arc adjacent to the weld. xiv. Tack the welded area correctly to ensure proper gap. xv. Proper welding sequence must be followed to reduce internal stresses and hence reduce warpage of structure. xvi. Always weld towards the free ends. 5.5.2 Weldability issues:  Grain growth in the HAZ and loss of toughness.  Reducing the heat input is critical and no preheats should be given.  Oxides formed during welding in the weld zone do not protect it from subsequent corrosion.  Proper protection of the weld zone from atmosphere and subsequent cleaning after welding are important.  Stringer beads to reduce the heat input.  Maintaining interpass temperature below certain temperature (in multipass weld). Also, allow weld to cool between the passes and using copper chills. 5.5.3 Preparation prior to Welding: The following points should be considered before welding of IRSM:44components. i. The area about 15 mm from each side of the weld zone should be properly be cleaned. ii. The weld area should be free from dust, dirt, grease, oil, paints etc. Any non-corrosive and suitable organic solvent (Kerosene oil, Benzene etc.) can be used for removing grease, oil & paints. iii. Only Stainless steel wire brushes should be used to remove tenacious layer of chromium oxide for better strength of joint. WAGON MAINTENANCE MANUAL APPENDIX-VI-GUIDELINES FOR MAINTENANCE & Page 11 of 14 REPAIR OF STAINLESS STEEL WAGONS iv. No edge preparation is required, unless specifically mentioned in the drg, when welding up to thickness 3/16"(5 mm approx.). For higher thickness between 3/16" & ½" (5-12mm approx.) bevel preparation is necessary. 5.5.4 Precautions During Welding: i. The welding parameter in the machine should be set as per recommendations of manufacturer. ii. If welding is carried out by MMAW process, connect the electrode with positive terminal of welding equipment (DC+) when welding with DC. iii. Use 70 OCV (min) transformers while welding with AC. iv. Keep the welding current on lower side (as possible) of the range as recommended by the manufacturer of the consumables. v. Maintain as short an arc length as possible to minimise the loss of alloying elements during welding. vi. Put stringer beads. Weaving should not be more than two times of the diameter of electrode used., vii. Use small diameter electrode according to thickness of base metal to minimise heat input& ensure minimal distortion. viii. Each run should be property de-slaged by using stainless steel brushes and chisels. ix. Preheating of job is not required. x. For cutting of stainless steels plasma cutting or machine cutting shall be used. Manual metal arc cutting may also be used in case when plasma arc cutting or machine facility is not available. 5.5.5 Precautions After Welding: i) The weld reinforcement of stainless steel welds must be grounded. ii) The stainless steels are susceptible to corrosion if the surface is rough. To avoid the corrosion, surface should be made smooth & polished. It is therefore, necessary to finish the stainless steel joint by grinding & subsequent polishing using fine grinder. iii) Post- weld cleaning should be undertaken on all weld areas (weld material and HAZ),arc strikes and points where cleats, lugs etc..have been welded. WAGON MAINTENANCE MANUAL APPENDIX-VI-GUIDELINES FOR MAINTENANCE & Page 12 of 14 REPAIR OF STAINLESS STEEL WAGONS 35.5.6 Electrodes For Welding: The welding electrodes to be used for repairs of IRSM:44 material are indicated below: S. Material to Electrodes/filler wire to be used be welded No 1. IRS M-44 to MMAW electrodes approved under classM1 as per IRS M-28-02 IRS M-44 shall be used. MMAW electrodes of diameter 2.5 mm/4.0 mm shall be used depending upon the thickness of the plate. Re-dry the electrodes before use to about 150°C for atleast one hour or as recommended by manufacturers. MIG/MAG welding filler wires approved under class VI as per IRS M46-03 shall be used. The diameter of the wire shall preferably be 1.2 mm/0.8 mm. 2. IRS M-44 to IRS M-41 As per G-72 Rev-3 or latest. 3. IRS M-41 to IRS M-41 Note: 1. The edge preparation should be done as per IS: 9595 for both “V” butt as well as fillet joints. 2. Electrodes and filler wires should be procured from any RDSO approved sources and the parameters like current, voltage, etc. should be as per IS code and manufacturers recommendations. 3. For other combination of materials welding Refer RDSO specification No.G-72 Rev-3 or latest appendix-III. 4. Welders` Qualification: Welders deputed to carry out welding work on wagons and wagon components should be only those tested and certified as adequately skilled for welding work on stainless steel wagons and its components. 5.5.7 During welding of dissimilar metals, the following general guidelines shall be helpful: i. Minimum heat input should be provided to joint, so that diffusion can be restricted and dilution is minimised. To achieve this low welding current, small diameter electrodes shall be preferred. ii. Proper filler materials compatible with both the steels, being joined are to be used. WAGON MAINTENANCE MANUAL APPENDIX-VI-GUIDELINES FOR MAINTENANCE & Page 13 of 14 REPAIR OF STAINLESS STEEL WAGONS iii. Dilution must be reduced to aslow as possible. Dilution depends on the welding process, process variables and penetration. Hence, proper welding process shall be used with proper setting of process variables (Current, Voltage, Travel speed, Polarity etc.). iv. When using gas metal arc welding (MIG/MAG) reduced current density is to be employed, so that only dip transfer of metal occurs. v. The problem of dilution and formation of inter-metallic phases can be minimised by buttering one or both joint faces with a layer of compatible material. 6. SURFACE PREPARATION & PAINTING i. The surface preparation and painting for underframe of the wagon shall be as per standard specification No.G-72 read with latest amendments. ii. Surface preparation of the wagon body Degreasing with petroleum hydrocarbon solvent to IS:1745-1978 (low aromatic grade 145/205) or any other degreaser (applicable for both SS,MS and corten steel). iii. PAINTING OF WAGON BODY Wherever the wagon is repaired it must be dressed to smooth surface and proper protective coating i.e. paints to be applied as recommended. For stainless steel As specified in the relevant drgs/ specifications or General Standard Specification No. G-72 (Rev.3) read with latest amendments. iv. The painting of bogies, couplers and air brake equipment shall be done as given in Para 11.2.5 of General Standard Specification No. G-72 (Rev.3) read with latest amendments. WAGON MAINTENANCE MANUAL APPENDIX-VI-GUIDELINES FOR MAINTENANCE & Page 14 of 14 REPAIR OF STAINLESS STEEL WAGONS References: (i) General guidelines for fabrication of stainless steel (IRS M:44) wagons and requirements for ensuring quality during manufacturing issued by Wagon Directorate, RDSO in Oct. 2007. (ii) Guidelines and facilities required for fabrication/maintenance of stainless steel wagons Issued by CAMTECH vide No. Camtech.M/W/SS Wagon-1.0 in December- 09. (iii) Maintenance Manual of LHB Coaches /Wagons a draft copy by CAMTECH/Gwalior. (iv) Welding procedure for joining various types of stainless steel parts with mild steel/corten steel parts used in carriage & Wagons based on procedure No. MC-97 Issued by M&C Directorate, RDSO, Luck now (v) Minutes of the seminar on welding technology-“Focus on Railway workshops”, held in Railway Board on 18.01.2011. (vi) General standard specification No. G-72, Issued by wagon Directorate, RDSO, Lucknow. WAGON MAINTENANCE MANUAL