PAINTING OF STEEL BRIDGES 1 Maintenance of Steel

PAINTING OF STEEL BRIDGES 1

Maintenance of Steel superstructures • Why? – Deterioration due to age – Rusting of steel • Oxidation of steel in presence of water and air – Rust is powdery and increases in volume – Rust is hygroscopic, promotes more corrosion 2

Corrosion 3

References • For existing structures: – IRBM 1998 para 217, 218 • For new structures: – IRS B 1 2001 para 39 4

Atmospheric corrosion • High humidity level ( > 65 %) • The corrosion velocity is doubled for every 10 o C increase in temperature. • Air pollution – SO 2 in air – The sulphur dioxide creates H 2 SO 3 which is oxidized to sulphuric acid (H 2 SO 4) which increases the corrosion velocity. • Similar effect of salts which come in from sea in coastal areas 5

Painting • Steel girders are more prone for corrosion – Where humidity > 60% – In coastal areas – Bridge across creek – Bridge situated in industrial environment – Girders subjected to • Droppings from traffic • Public nuisance 6

Planning of painting • Frequency 1 yr to 6 yr as prescribed by the Chief Engineer – Depending on the severity of corrosive environment 7

Types of Painting • • • Patch painting Scraping and painting Cleaning and painting Metallising Epoxy painting – The first three are using ordinary paints 8

Planning of painting • If a small portion of the girder found corroded during inspection, but girder not due for painting, Patch painting to be done 9

Planning for Painting 10

Surface preparation • Aims of Surface preparation – To clean the surface off any rust, moisture, loose/perished paints etc – To give sufficient roughness to the surface to be painted for better adhesion of the paint – The paint barrier must be complete, uninterrupted and strongly adhering to surface to provides effective protection 11

Scraping and Cleaning Areas to be decided Scraping Cleaning 12

Planning of painting • Scraping to be done where the existing paint film is deteriorated • Only cleaning to be done where the existing paint is satisfactory • Scrapping area shall be decided in advance of start of painting and advised to contractor 13

What to do in sleeper seat? • Hidden parts under sleeper to be exposed by shifting – Sleepers shifted and sleeper seat painted. After drying of paint, sleeper shifted back – Damages fittings and affects track parameters – Sleepers seat painting to be done by the SE (PWAY) (at reduced frequency, once in 2. 5 years*) * W Rly Practice • Metallising/ epoxy paints shall be used for better life of paint in sleeper seat 14

Surface preparation • Scraping – Remove all rust, loose/perished paint, any other surface contaminants • Tightly adhering paint can remain – Use emery paper, wire brush, scrappers – Use power tools – Flame cleaning – oxy-acetylene flame (not to be done on plates with thickness<10 mm) – Luke warm water – 2% detergent – Surface shall be as per St 2 in IS: 5909. • Primer as well as top coats to be applied 15

Surface preparation • Cleaning – Remove the external impurities clinging to the painted surface. – Paint condition is good, so not to be removed – Surface roughness is to be improved – Use wire brush, cloth rags, water etc • Only top coats to be applied 16

Precautions during painting • Surface preparation key to the performance of the paint system – Upto 80% contribution • Painting not to be done during rainy weather and in dusty winds/ foggy/ misty conditions – Relative Humidity shall be less than 90% – Moisture/ dust etc shall not be included in the paint film 17

Precautions during painting: paint quality • Paints from approved suppliers in RDSO list shall only be used – Paints shall conform to relevant IS codes – Test certificates and original bills may be taken – Markings on drum shall be seen – Paints must be stored properly Contd. . 18

Precautions during painting: paint quality – Outside testing may be got done if doubt is there on quality or source of paint – Turpentine and kerosene must not be added as thinners. • Only approved quality thinners from the same manufacturer may be added if the need is felt at site (due to very high temperature etc) 19

Paint to be used within shelf life • Paint red oxide – 1 year • Aluminium – When paste & oil not mixed – 1 year – When mixed – 4 months • Other paints – As per manufacturer recommendations 20

Precautions during painting: painting • Paint film thickness shall be checked? ? – No thicknesses specified – Varies with type of surface, paint manufacturer, method of application, temperature/ humidity at time of painting etc • Trial shall be conducted for the surface and the brand of paint for monitoring during work • Initial and final readings shall be taken with elcometer – Paint consumption shall also be monitored to get the idea of quality 21 – Drums may be kept by rly till work is

Application of Paint • Good quality brush with minimum width 5 cm • Brush shall be held at 45 deg to the surface – Light strokes – One coat shall mean two layers, second one cross wise – Uniform and even painted surface shall be obtained – Can be sprayed or rollers can also be used • Rags, cotton waste, cloth etc shall not be used 22

Time lag between stages of painting • Maximum time – Surface prep (scraping) and Primer – 24 hours – Surface prep (cleaning) and first finishing coat – 48 hours – Primer coat and 1 st finishing coat 7 days – 1 st finishing and 2 nd finishing coat } • Paint layer shall be applied only after sufficient drying of the earlier paint layer • Even for prepared surface, there may be contamination – Must be cleaned during painting 23

Temporary coating • If due to some reason, the painting cannot be taken up immediately after the surface preparation – Temporary coating of linseed oil shall be applied thinly and uniformly – 1/3 litres per 10 sqm shall be sufficient 24

Painting Scheme: No Severe corrosion • Priming coat – One coat of Zinc chromate priming to IS 104 followed by red oxide zinc chrome priming to IS 2074 OR – Two coat of Zinc chromate red oxide primer to IRS P 31 • Finishing coat – Two cover coats of red oxide paint to IS 25 123

Painting Scheme: Severe corrosion • Priming coat – One coat of ready mixed paint zinc chromate priming to IS: 104 followed by one coat of red oxide zinc chrome priming to IS: 2074 • Finishing – Two coats of red oxide paint to IS: 123 or aluminium paint to IS 2339 26

Lead paints • Red Lead paints are not available in market • These were replaced by Zinc Chrome priming to IS: 104 followed by Zinc Chrome Red Oxide priming to IS: 2074 in IRBM vide correction slip no 12 • Even Red Oxide paint to IS: 123 is difficult to get in market 27

Painting During Fabrication • Para 20. 1 of IRS B 1: All permanent contact surfaces shall be removed of paint and mill scale, cleaned, dried and immediately a layer of Zinc Chrome Red Oxide Priming to IS: 2074* shall be applied *Correction vide CS no 2 to IRS B 1 (As Red Lead paints not available in market) • Also Para 39. 3 of IRS B 1 28

Painting During Fabrication • Same painting schedule as already shown, depending on the severity of corrosion at location where girder will be inserted 29

Superior paints 30

Superior Paints • Metallising • Epoxy Painting • Should be done for girders exposed to corrosive environment – Flooring system ( cross girder and rail bearer) in open web girders – Steel girders in industrial, suburban or coastal areas • Also may be done for – Top flange plate of plate girder and underslung girder – Top bracing system in open web girders in electrified areas 31

Cross girder 32

Bridge in corrosive environment 33

Bracings in electrified area 34

Top flange of plate girder 35

Metallising Spraying of molten Aluminium on cleaned surface 36

37

Metallising • Surface preparation –Remove Oil/ grease from metal surface using petroleum hydrocarbon solvent to IS: 1745 –Cleaning by blasting the surface with chilled iron grit to G 24 (grit blasting) or with sand (sand blasting) 38

Surface preparation • Sand/ grit Blasting – Best type of surface preparation – Use air to blast clean the surface with • sand between mesh sizes 12 to 20 (40% retained on size 20) or • chilled shots to G 24 as per BS: 2451 – Surface to be clean of all layers including mill scale – In exceptional cases, if sand blasting not possible, power tool cleaning shall 39

COMPRESSOR Equipment CHILLED IRON GRIT (MAGNIFIED) SILICA SAND HOPPER 40

Sand vs Grit Blasting • For small components, grit blasting shall be done – Grit blasting has to be done in enclosure for collecting the shots for reusing. • For large components and on-site, sand blasting shall be done • Issues – Causes silicone particles in air, bad for health – Shall be done with adequate precautions • Not cause too much problem to railway users. 41

Blasted Surface: Shall be to Sa 2½ as per IS: 5909 42

Scraping vs Sand blasting • Sand blasting is very costly – Use sand blasting for expensive paint systems • Use scraping and cleaning for Ordinary painting – Also for expensive paints in inaccessible locations 43

Blasting Parameters • Spray sand/grit with pressure to remove rust, paint and other foreign particles – Nozzle Pressure: Not less than 2. 109 Kg/sq cm – Nozzle Dia: Not more than 12 mm – Nozzle Position: At Right Angles to surface, Approx 22. 5 cm away. 44

Blasting 45

Metallising • Metallising done using special gun – Has acetylene/ LPG, Oxygen and Air feeds – Aluminium wire fed separately – Heat from fired LPG/ Acetylene melts the aluminium wire – Molten metal sprayed by air pressure onto prepared steel surface. 46

Metallising Gun 47

Metallising being Done 48

Metallising • Parameters for Spraying Aluminium – Air Pressure: Not less than 4. 218 Kg/sq cm – Wire dia 3 mm or 5 mm – Aluminium wire 99. 5% pure as per BS: 1475, material 1 -B or as per IS: 739 – In minimum two layers – At least one layer within 4 hrs of blasting, and finishing within 8 hrs of blasting 49

Metallising • Check coating thickness using any magnetic thickness gauge. – Thickness minimum 115 microns – Thickness average 150 microns 50

Painting over Metallising • • Clean the surface free of any sand etc Etch primer to IS: 5666 Zinc chrome primer to IS 104 Two coat of aluminium paint to IS 2339 – If metallising is being done in workshop, one coat shall be applied in shop and the second after erection at site 51

Maintenance Painting over metallising in service • If the top coat is OK, the aluminium layer shall be renewed once in five years or as specified • If existing paint flaked or damaged, wire brush shall be used to remove it and primer + aluminium paints shall be applied • If large areas rusted, only then scraping shall be done for painting. In such a case, metallising may be done again. 52

Inspection of Metallised Surface • During inspections, no hammers shall be used including rivet testing hammers as the metallising may be damaged – Loose rivets shall be seen by signs of rust under rivet head etc 53

Epoxy Painting Epoxies are having very good adhesion and provide good corrosion protection 54

Epoxy painting: Surface preparation • Remove oil/grease using petroleum hydrocarbon solvent ( IS 1745) • Prepare the surface by suitable blasting 55

Epoxy painting • Primer coat – Two coats of Epoxy zinc phosphate primer to 60 micron min. (RDSO M&C/PCN-102/ 06) – Provides adhesion to surfae • Intermediate coat – One coat of micaceous iron oxide to 100 micron. (RDSO M&C/PCN-103/ 06) – Provides corrosion protection 56

Epoxy painting • Finishing coat • In coastal areas: Two coats of polyurethane aluminium to 40 micron. (RDSO M&C/PCN-110/ 06) • In other areas: Two coats of polyurethane Red Oxide to 40 micron. (RDSO M&C/PCN-109/ 06) – Provides gloss, abrasion resistance and UV protection 57

Maintenance painting • During maintenance, if epoxy paint is flaked or some damage is seen, the same shall be repaired by the manufacturer’s approved paint. • If large areas rusted, complete epoxy painting may be done again. 58