Docfoc.com bgas question and answer

BGas Painting Inspection Grade 2 / 3
1. Name the different ways of surface Preparation?
Dry Abrasive Blast Cleaning
Water Blasting
Hand and Power Tool Cleaning
Flame Cleaning
Pickling ( Chemical Cleaning )
Vapour Degreasing
Weathering
2. What equipment are needed for Blasting?
Compressor
Blast Pot - for abrasives
Vapour Traps ( knock out pot )
Hose
Nozzles
Safety to 1GE SR 21 – Maintain operating pressure at 100 psi.
Hose should be carbon impregnated.
External couplings.
dead mans handle should be under direct control of the operator
should be kept as straight and as short as possible to avoid kinks, and
blowouts.
PPE (leather aprons and gloves, boots and ear protectors, including
direct air fed helmet, with adequate visors.
3. What speed do the particles exit a Venturi blast nozzle?
450 mph ( 720 kmph )
4. What speed do the particles exit a Straight bore nozzle?
220 mph
5. Describe how you would carry out a check on air pressure of a blasting?
Alert the Operator
Shutdown the abrasive
Insert the Hypodermic needle gauge into the reinforced hose as possible to the nozzle at 45°
toward the nozzle Take direct reading from the gauge
6. What are the advantages and disadvantage of Venturi?
Venturi
Advantages Disadvantage
Very high speed (450mph) Safety
Faster operation Maintenance
Large area coverage less accurate
Large blast pattern
Suitable for large area
7. What are the advantages and disadvantage of Straight bore?
Straight bore
Greater accuracy Low speed ( 220 mph )
less area coverage
1

8. What is used to determine the presence of Hygroscopic salts, in industrial situation?
Potassium Ferricyanide test will determine the presence of Hygroscopic salts, in industrial
situation?
9. Which test is carried out for soluble salts in a marine environment?
Silver Nitrate Test is carried out for soluble salts in a marine environment
10. Give another common name for Copper slag?
Iron Sillica
11. How many photographs of Flame clean standards are in BS 7079?
There are 4 photographs of Flame clean standards are in BS 7079
12. Name the system for pickling followed by passivation?
Duplex process system is pickling followed by passivation using phosphoric or chromic acid
13. Describe how rouge peaks are caused?
Girt, which cuts the profile.
14. How many times can garnet be used for site blasting? Why?
One time only, because after blasting the garnet fall on the ground & it gets contaminated. And
we can’t use contaminated abrasives for blasting.
15. List the equipment required for an abrasive blasting operations site?
A compressor
A pot containing the abrasives.
Vapour Traps for oil and water (knock out pots).
A hose, usually carbon impregnated to discharge static electric
External couplings
A nozzle
A dead mans handle for operator safety.
16. When power brushes are authorised for use BGas/Transco site, the wire is made from which non-
sparking producing materials ?
Phosphor bronze and Beryllium bronze
17. What are the advantages and disadvantages of wet blasting ?
Wet Blasting
Useful for removal of toxic materials Need large amount of water
Environmentally friendly Disposal of resulting slurry
Spark free Does not cut profile
Ideal for removal of soluble salts & chlorides Substrate inhibitors to be added
18. What profile range can be measured using coarse Testex?
20 – 50 um profile range can be measured using coarse Testex
19. What profile range can be measured using X coarse Testex?
37 – 115 um profile range can be measured using X coarse Testex
2

20. What are the two principles of the theory of Adhesion?
Molecular Interference ( PHYSICAL )
Molecular Attraction ( CHEMICAL )
21. Briefly Describe the mechanisms of the two theories of adhesion.
Molecular Interference : The surface is rough & uneven the paint wets & lock into profile
analogy Velcro, PHYSICAL
Molecular Attraction : Negatively charged particles attracts to positive areas& vice versa.
Analogy magnet ( also called as Ionic Bonding ). CHEMICAL
22. How many microns are in 1thou?
1thou = 25.4 um
23. Give three different names for the cross section of a blast.
Anchor pattern.
Surface profile
Key
Peak to trough height
Amplitude
24. What is the most common cause of flash rusting on a blasted substrate?
Rouge peaks
25. What would be considered to be an ideal shot grit mix?
What is the purpose of mixing shot and grit?
To get uniform profile, because grit cuts the profile & shot controls the rouge peaks.
26. Which abrasive would have the effect of work hardening a substrate?
Metallic Shot
27. Name three methods of measuring or assessing a profile.?
1- By using surface profile Needle Gauge
2 - Using Testex tape & Dial micrometer
3 - Comparators
28. What is the most common cause of rogue peaks on a substrate?
Grit, which cuts the profile
29. In what situation would it be better to use steel grit in preference to copper slag abrasives?
Copper slag can be used only once, because it shatters into small pieces on impact. So Grit it can
be used many times
30. If cracks or laminations are found on a substrate after blasting what steps should be taken?
Cracks or laminations must be referred to the Engineer
31. Using comparators to ISO 8503, what are the three main profile assessments?
1- Fine
2 - Medium
3 - Coarse
3

32. What are the other two assessments when the above three are not appropriate?
1 - Finer than Fine
2 - Coarser than Coarse
33. What would be size of copper slag needed to give a profile of 50 to 75 um?
G – 16 would be size of copper slag needed to give a profile of 50 to 75 um
34. What is the title of the BS 7079?
The title of the BS 7079 is Preparation of the Steel substrates before application of paint
35. Describe the four Blasting grade ?
Sa1 : Light Blast Cleaning
Sa2 : Thorough Blast Cleaning.
Sa2 ½ : Very Thorough Blast Cleaning.
Sa3 : Blast Cleaning to Visually Clean Steel.
36. What are the four characteristics of an abrasive?
Size
Shape
Hardness
Density
37. Why are blast hoses carbon impregnated?
To discharge static electricity
38. Name the gauge used for measuring pressure at the blast nozzle?
Hypodermic Needle Gauge
39. Name four advantages of centrifugal blasting over open blasting.
1 - Operator Safety
2 - System is more productive
3 - Quality can be adjusted
4 - Efficient use of Abrasives
40. According to BS 7079 is it possible to blast clean to an A Sa1?
Not Possible ( According to BS 7079 is it possible to blast clean to an A Sa1? )
41. Is there any difference between an A Sa1 and B Sa1?
A Sa1 – Not achievable
B Sa1 – Can be achievable
42. Could you tell the difference between rust grades A and B blasted to Sa3?
No Difference
43. Could you tell the difference between rust grades C and D blasted to Sa3?
C – Slight pitting
D – Heavily Pitted
44. What would be a typical speed of abrasives leaving a wheel abrator?
220 mph
4

45. What is considered to be the most efficient blasting pressure?
100 psi is the most efficient blasting pressure
46. What is meant by the term “burnishing”?
Burnishing means Polishing
47. What would be the equivalent to St2 in the Sa grades?
St2 is equivalent to Sa 2 ½ grades
48. What is the neutral figure on the pH scale?
7 is the neutral figure on the pH scale
49. How is pH measured?
pH measured using indicator strips
50. Why are inhibitors sometimes added to water in wet blasting?
Sometimes inhibitors are added to water in wet blasting, because to retard corrosion
51. Name two typical areas where needle guns might not be used?
Rivets & bolts, Weld end preparations
52. What is the Duplex Process of surface preparation?
Duplex process system is pickling followed by passivation using Phosphoric acid or chromic
acid.
53. Why is it considered essential to remove millscale prior to painting?
Millscale being cathodic to steel and more noble than steel.
54. Which British standard would be used in determining the size of copper slag abrasive?
BS 410 (specification for test sieves)
55. Which British standard would be used in determining the size of metallic abrasive?
BS 410 (specification for test sieves?
56. Why it is important to have a good surface preparation?
Because good surface preparation provide area available for adhesion and for coating life.
57. What is meant by the term grade, relating to a blast finish?
Degree of cleanliness, Degree of roughness (surface profile)
58. What are the main factor governing the grade of a blast finish?
Time, Velocity of particles.
59. Name four advantages of centrifugal blasting over open blasting?
60. Operator safety, more productive, efficient use of abrasives, quality obtained.
61. which solvent are commonly used for degreasing?
Xylene.
62. How is abrasive cleansed in a wheel abrator system?
By Air wash separator.
5

63. What would be the typical temperature and concentration of sulphuric acid in the pickling
process
70C, 5-10% concentrated sulphuric acid, 5-25 min.
64. Describe the “Duplex Process”?
Clean surface by solvent (xylene)
immerse the component is sulphuric acid 5-10% concentration, 60-70C temp, 5-25 min.
rinse with clean warm water to remove layer of soluble salts formed.
immerse in bath of phosphoric / chromic acid 2% at 80 C temp., 1-2 min with iron filling (0.5%)
rinse in clean water and check PH value.
65. What would be considered to be advantages of wet blasting over dry blasting?
Wet blasting removes toxic materials, more environmentally friendly, spark free and ideal for
removal of soluble salts etc.
66. Why is the phosphating or chromating of a steel done?
It forms a rust inhibitive layer which protect the underlying surface and increase the adhesion
properties & prevent embrittlement.
67. Name a third type of paint other solvent free and solvent borne?
Powder paint.
68. Name four or more advantages of chlorinated rubber paint?
Resistance to mould growth.
Non-flammable after solvent release.
Very high resistance to acid & alkalies
Material is non-toxic & provides a very durable film.
69. What are the three main disadvantages of chlorinated rubber paint?
Low resistance to solvent.
Low temperature tolerance, 65C maximum.
Spray application resulted in ‘cobwebs’
70. Would it be good practice to apply chlorinated rubber over alkyd resin?
No.
71. What is meant by opaque?
Hiding power, covering power (opacity)
72. What is another name for an un-pigmented paint?
Varnish
73. What are the natural properties of a resin?
Brittle by nature and fast drying, mix with oil to modify some properties.
74. What are the natural properties of an oil?
Slow drying properties, mixed with resin to modify the film properties.
75. How does the paint using the barrier principle work?
The material form a thick impermeable layer of a high electrical resistance.
76. How does the paint using the passivation principle work?
6

Chemical reaction between the paint constituents and the substrate.
7

77. How does paint using cathodic protection principle work?
Bi-metallic principle by using less noble metal.
78. Give another name for solvent free two packs?
MCL - Multi compound liquid
79. Name six properties of binder?
Viscosity
Adhesion to the substrate for the expected life of coating.
Resistance to chemical attack.
Dialectric strength.
Resistance to passage of water.
Cohesive strength.
Resistance to abrasion.
80. Name three natural resin used in paints?
Copals, Dammers & Coumarones.
81. Name five natural oil used in paints?
Linseed Oil, Tung Oil, Soya Oil, Tall Oil & Safflower Oil.
82. Name an Inorganic high temperature service binder?
Ethyl & Methyl silicate (silicone)
83. Name two pigments likely to be used for high temperature service?
Aluminium & Carbon.
84. By what name would you call the basic unit of a polymer?
monomer (mer).
85. what is polymerization?
Joining together of a string or structure of repeated units.
86. What would be the characteristics of a short oil paints?
less than 45% oil to resin, brittle and fast drying material.
87. What would be the characteristics of a long oil paints?
More than 60% oil to resin, slow drying properties, decorative material.
88. What is meant by the term opaque pigment?
Inert particle with excellent light scattering properties in order to give covering power (opacity).
89. What is the typical size of a pigment particle?
1/10 micron.
90. Briefly describe the difference between saturated and unsaturated when referring to oil or
polymers?
Saturated oil are oil which cannot combine with oxygen to form a film and unsaturated oil combine
with oxygen and solidify by polymerization to form film.
91. What is the main difference between a dye and a pigment?
Pigment used in paints must remain as solid particles within the vehicle (solvent + binder), and
not dissolve, if is dissolves it is known as a dye.
8

92. Name three rust inhibitive pigments considered to be toxic?
Red lead, Calcium plumbate, coal tar & zinc chromate.
93. Name four commonly occurring minerals used as extender pigments?
Clays, chalk, talcum & slate flour.
94. If pigments was added way below the CPVC, how would it affect the film?
Good gloss properties but poor covering power (opacity), low cohesive strength.
99. The abbreviation CPVC means what?
Critical pigment volume concentration.
100. Why are thixotropes added to a paint formulations?
To stop settlement and allow higher film thickness.
101. Describe how a basic inhibitor works?
Causing a chemical reaction between the paint constituent and substrates.
102. Which of the common extenders could not be used in whites and pastels?
Slate flour (black colour).
103. How would the film affected if pigment was added above the CPVC?
Film would be porous, low in cohesive strength and adhesion.
104. Which of the rust inhibitive pigments is the most common?
Zinc phosphate.
105. Why are extenders used in paint formulation?
Provide adhesion, cohesion, film strength and durability.
106. If chromium was used as a pigment, what colour would the paint be?
Green, yellows & Oranges.
107. Why are plasticizers added to paint?
Flexibility, reduce brittleness, compatible with binder
108. Two metals are commonly used as galvanic pigmentation, name them?
Zinc & Aluminium
109. Why are driers added to oil based paint?
To allow even thorough drying of the film.
110.What is meant by the term thixotropic?
Thixotropic is an anti settling agent, a thickener, allows a higher film thickness eg bentones &
waxes.
111. What is meant by the term aggregate when referring to paint?
Degree of dispersion of fineness of grind.
112. If antioxidant was added to paint, what would it do?
Antioxidant retard the formation of a skin on the surface of the paint eg. Methy ethyl ketoxime.
10

113. Give names of two plasticizers?
Castor oil, coconut oil and palm oil.
114. What is meant by the term dispersion?
A paint consist of solid particles suspended in the vehicle, where there is no solubility, so a paint is a
dispersion.
115. There are two types of dispersion, what are they?
A dispersion can be either a solid or liquid dispersed within another liquid, where there is no
solubility.
116. If paint cures by chemical reaction is it reversible or convertible?
Convertible or non reversible.
117. What type of polymerization occurs in chemically curing paint?
Cross linked polymers.
118. Name a paint, which dries solely by solvent evaporation?
Chlorinated rubber, vinyls, acrylics, cellulosic and laquers.
119. What is meant by non-convertible?
Dries solely by solvent evaporation, no chemical reaction.
120. What is meant by non-reversible?
Cures by oxidation and Chemical reaction.
121. Name four drying mechanisms?
Solvent evaporation, oxidation, chemical curing and coalescence.
122. In a coating, which dries by solvent evaporation, what type of polymerization occurs?
Linear polymers.
123. What is another name for fineness of grind?
Degree of dispersion.
124. Which generic types of paint dry by solvent evaporation followed by oxidation?
Alkyds, phenolics, natural oil and resins.
125. What type of polymers forms during oxidation?
Cross linked polymers.
126. What term applies to paint drying at ambient temperatures?
Air drying.
127. What is meant by the term coalescence?
Physically join together.
128. What is meant by the term pot life?
Pot life is the period of time after mixing in which the paint must be used.
129. Name three curing agents used in epoxies?
Amides, Amines and Isocyanates.
11

130. Is paint a solution or dispersion, qualify?
Dispersion, pigment particle remain in as solid in a vehicle.
131. What is an exothermic reaction?
heat off from the container.
132. What is meant by the term induction period?
The length of time after mixing which the paint should stand before use.
133. What is the difference between thermoplastic and thermosetting?
Thermosplastic material soften with the application of heat, therefore reversible or non convertible
Eg. Polyethylene and polypropalene
Themosetting means the material will cure with the application of heat, therefore are convertible or
non-reversible eg. Epoxy and urethane.
134. Two other terms relate to induction period, what are they?
Stand time and lead time.
135. Does a phenolic resin have an induction period?
No.
136. Name some reversible binders?
Chlorinated rubber, vinyls, cellulose etc.
137. Is an epoxy powder paint thermoplastic or thermosetting?
Thermosetting
138. If a coating is permeable, what does it mean?
Allow water to penetrate to the substrate.
139. What is meant by cross-linking, give two binders as an example?
Cross linking or chemical curing is a three dimensional polymerization process eg. Epoxy &
urethane.
140. What is the opposite to exothermic?
Endothermic.
141. What is the term used for paints needing temperature in excess of 65C to cure?
Stoving.
142. Name a material used as a driers in paint formulation?
Octoates, manganese and zirconium.
143. Why would bentones or wax be used in paint formulation?
Used as anti settling agents.
144. What generic type of paints would use anti-oxidants?
Alkyd, natural oil, resin
145. How does a single pack, epoxy ester paint dry?
Oxidation.
12

146. How is dew point defined?
The temperature at which water vapour in the air will condense.
147. When using a whirling hygrometer which bulb should be read first and why?
Wet bulb, the water in the wet bulb uses heat energy from the air to change into water vapour.
148. At what speed should the thermometer bulbs pass through the air?
4m/sec.
149. By what other name can we refer to a whirling hygrometer?
Aspirated hygrometer or psychrometer.
150. What is the stated criteria for acceptance, prior to calculations on a whirling hygrometer?
On two consecutive spin the reading should be within 0.2C, wet bulb to wet bulb and dry bulb to dry
bulb.
151. Name two pieces of equipment used for taking steel temperature?
Magnetic and digital.
152. Define viscosity?
Viscosity is defined as being a fluid resistance to flow.
153. Approximately, what is the viscosity of water?
One centi poise
154. Name the cgs and SI units of dynamic viscosity?
Poise, centi poise, dyne, N. s/m2.
155. Name three different flow cups?
Zahn, Frikmar, Ford, ISO and DIN
156. When using a flow cup which unit of viscosity would be used?
Second.
157. In ford flow cup no 4 what does 4 relate to ?
Hole size in mm.
158. Give the names of three different rotational viscometers?
Rotothinner, Kerbs Stormer Viscometer and Flow viscometer.
159. Give a reason for performing a viscosity test on site?
To obtain the percentage of thinner used.
160. Which viscometer would not be used on thixotropic paint?
Flow viscometer.
161. Why is temperature very important when doing viscosity tests?
Increase or decrease in temperature will effect the viscosity.
13

162. What is the main difference between the rotathinner and krebs stomer?
Rotothinner measures dynamic viscosity and kerbs stomer measures kinematic viscosity.
163. Describe how to use a ford flow cup?
Level the stand and cup. Place another cup under the flow cup to catch the paint, fill the cup with
paint ensuring it is full whilst covering the 4mm hole in the bottom. Run a straight edge over the lip
of the cup to ensure it is full simultaneously remove finger from bottom and start stop watch. Time
until 1st
break in flow. The time recorded is the viscosity in seconds at the temperature.
164. Give another name for a fineness of grind guage?
Hegman grind gauge
165. How and for what is a hegman grind gauge used?
Paint is added to the deepest point of the scale and drawn along to totally fill the groove using a
specially profiled scraper bar. Within 3mm band, five to ten aggregates break through the surface of
the paint, this is the point where surface will change from gloss to matt, thus measuring the degree of
dispersion of paint.
166. Briefly describe how to do the volatile, non-volatile test to BS 3900 Pt B2?
A dry glass stirring rod and watchglass along with 2gm of paint is weighted, watchglass containing
paint is place into a hot air oven, stir to drive away volatile content, take a final weight of the glass,
rod, and dry paint and simple calculation will give volatile / non volatile ratio by weight.
167. Name the equipment used to determine the flash point of a solvent?
Abel cup.
168. What colour should the flame be at the flash point?
Blue colour.
169. What formula is used to calculate the density?
Density = Weight / volume
170. What formula is used to calculate specific gravity?
Specific gravity =Density / Density of water
171. What is relative density?
Weight of material divided by of volume of water
172. What are the other names for a density cup?
Relative density cup, specific gravity cup, weight per liter cup, weight per gallon cup and
pyknometer.
173. What is a stoke, the unit for ?
A viscosity unit frequently used for kinematic viscosity is the stoke. (kerbs units or poise).
174. Which test is used to determine Abrasion resistance?
Taber rotary abraser.
175. Which equipment would be used to determine flexibility?
Cylindrical mandrels.
14

176. Which equipment would be used to measure impact resistance?
Tubular impact testers.
177. For what reason would the Koeing albert apparatus be used?
To test the hardness of a film.
178. For which two reason could a density cup be used on site?
To calculate the density of the solvent.
To calculate the 2 pack are mixed in correct proportion.
179. Name four accelerated test boxes?
Humidity cabinets, salt spray cabinets, water soak tests, temperature cycling and prohesion testing.
180. Why would a tropical box be used?
For testing tropical conditions.
181. Would a paint be higher or lower density than water?
Higher
182. How would the density be affected if solvent was added to paint?
The density of paint decrease
183. What is the capacity of a density cup?
100 cc.
184. What difference is there between SG and Density?
185. What information could be obtained from a water soak test?
Painted panels submerged to test for water absorption.
186. What information could be obtained from temperature cycling test?
Maximum and minimum temperature can be set and cycle time, over a running period to 1000 hrs.
187. What information could be obtained from a cold check test?
188. Name four drying and curing tests?
Mechanical thumb test, Pencil scratch test, mechanical scratch test and gold leaf test.
189. What stage of the BK test would be recorded as the drying time?
Solvent Evaporation time, the solgel transition, surface drying time and final dry time.
190. Name three methods of determining opacity?
Trough type, black and white fused plate and cryptometer.
191. What effects the opacity of a paint film?
Pigment volume concentration.
192. Why would a Pfund cryptometer be used?
To measure Opacity.
193. Give one reason why an inspector would use a PIG gauge?
To measure MIO.
15

194. Why are wet paint film thicknesses needed?
To ensure that the DFT would be ok.
195. Name two methods of measuring WFTs?
Eccentric wheel and comb gauge.
196. What is the reason for taking WFT immediately after application?
To obtain true readings (solvent start evaporating as it exits the spray tip).
197. Can a banana gauge be used on non-ferromagnetic substrate?
No.
198. Could an eddy current gauge be used on ferromagnetic substrates?
No.
199. Can a horseshoe gauge be used on non-ferromagnetic substrates?
No.
200. As part of which test would a bar applicator be used?
Opacity.
201. Which instruments would be used to measure reflectivity?
Gloss meter.
202. How does a gloss meter work?
A light source direct a beam of light onto the surface under test and a photo cell, set at the same
angle, collect the reflected light and quantifies it and convert it digitally into a percentage of the
incident light. A high percentage of reflection will be gloss and a low percentage will be matt.
203. Which factors in paint govern the degree of gloss?
Degree of dispersion, resin type and PVC
204. In a primer/mid coat what would be the expected degree of grind?
40-45.
205. In a gloss paint what would be a typical degree of grind?
20.
206. What percent reading would be expected when measuring gloss on a glass panel?
Near 100%
207. Using a gloss meter a reading of 25% would signify what?
Matt.
208. If an aggregate size of 35 um was present in a paint of 30 um DFT what would be a likely
result when using a gloss meter?
Matt.
209. Name three common tests for determining adhesion of a paint film?
V cut test, cross cut and dolly test.
16

210. Which adhesion test are quantitative?
Dolly test and hydraulic adhesion test.
211. Inter coat adhesion and primer to substrate adhesion are two adhesion faults name the third?
Cohesive failure.
212. What chemical solution is used to conduct a cathodic disbondment test?
Sodium chloride.
213. What criteria is used when assessing a cathodic disbondment test panel?
214. Name the methods of applying cathodic protection?
Sacrificial anodes system and impressed current system.
215. What is used to determine the potential of a pipeline?
Copper sulphate half –cell electrode.
216. Would it be advisable to refill a pipe trench with carbonaceous backfill?
217. Does a cathodic protection system eliminate corrosion?
It controls where corrosion occurs.
218. Can the external surface of a tank be protected?
No, In order for cathodic protection to be applied, an electrolyte must be present.
219. What voltage would be used on a 250 um thick paint using a sponge pinhole detector?
9V.
220. What voltage would be used on a 450 um thick coating with sponge pinhole detector?
90V.
221. What function does the above additive perform?
Surface tension.
222. Would it be advisable to do wet sponge detection on galvanizing?
No.
223. Does a sponge detector work on AC or DC?
DC.
224. Other than the wet sponge which other equipment could be used to determine the presence of
pinhole/holidays?
Spark detector (high voltage)
225. Name two categories of paint mill?
Ball mill and attritor mill.
226. What is the main reason for processing paint in a mill?
Dispersing or Grinding or milling aggregates and agglomerates down to a suitable size for the paint.
17

227. Briefly describe how a ball mill works?
Mill base is added to the drum until the balls are covered, about 50% capacity of the drum. The hatch
is then sealed off and the drum started rotating at such speed so that the balls cascade down and do
not stick on the drum due to centrifugal forces. Shear forces are applied to the mill base as the balls
cascade between the balls and vessel walls. A typical dispersion time would be overnight.
228. Briefly describe how a attritor mill works?
The attritor mill is a vertical version of the ball mill, but more efficient and also static. The balls are
driven by paddles. The mill base is continually circulated by pump from bottom to top and gives
adequate dispersion in less time.
229. A bead mill is sometimes called by which other names?
Sand mill or pearl mill.
230. How does a colloid mill work?
Using grinding discs containing carborundum, approx. 10” diameter. The top stone is stationary and
the lower stone is rotating fast at a speed up to 3600 revs per/min. Gravity fed low viscosity slurry
enters the centre of the top stone and is passed between the two stones by centrifugal force, where it
is subjected to extreme turbulence and shear forces to affect the dispersion.
231. What do you understand from the term halogenated hydrocarbon?
232. How can we determine the viscosity of a high viscosity paint?
233. Briefly describe the principle of CP?
A metal less noble than steel is included in the film and an electrolyte eg. Water passes through the
film contacting substrate and pigment particle, then a circuit can engaged whereby the pigment
particles will receive the hydroxyl iron and thus suffer corrosion in preference to the steel substrate.
234. What function does a primer have in a paint system?
Primer is normally low volume solid material, wets out substrate and provide excellent adhesion and
also provide a key for any subsequent layer.
235. In a mordant primer what is the main working constituent?
Mordant means of a corrosive nature or will bite into and as suggested contains an acid, phosphoric
acid.
236. What advantages do electrostatic application methods provide?
The coating material is positively charged and is attracted to the component when using powder
coatings, wastage is significally reduce and it produces a more uniform coating.
237. Define exothermic?
Giving off heat, the container will warm up.
238. Define endothermic?
Taking in heat, the container will cool, forming condensation.
239. What is cohesive failure in paint give the main cause?
Over thickness of a layer can entrap solvent during drying process and stop formation of film,
reducing cohesive strength. The main reason for cohesive failure is solvent entrapment and incorrect
ratio mix to two pack.
18

240. Why does a zinc rich paint need a strong binder?
241. Why are etch primers not spray applied?
242. What do you understand by the term over spray?
243. Name four methods of determining DFTs?
Test panels, Calculations, Destructive test gauges & non-destructive test gauges.
244. What is a psychrometer used for?
Psychrometer or whirling hygrometer used to determine wet and dry bulb temperature from which
relative humidity and dew point is calculated.
245. What colour should a galvanized surface be after application of ‘T’ wash?
246. How soon can ‘T’ washed substrate be coated?
247. Other than pigment, base and curing agent name two other constituents fo FBE powder paint?
248. Give the main differences between airless and conventional spray.?
Conventional spray Airless spray
Slow application Excellent application rate
Low air pressure 40-75 psi Can need 100 psi to operate pump
Delivery pressure greater than 20 psi Delivery pressure greater than 6000 psi
Need special paint container use manufacture container
Low maintenance high maintenance
Easy to clean need flushing to remove traces of paint.
249. Brush application has advantages over spray application, what are they?
Environmentally friendly, less waste of material, any dust or detritus on the substrate present worked
in to the film.
250. What is the main consideration when selecting a metallic pigment for a sacrificial paint?
The metallic pigment must be less noble (more electronegative)
251. What is mean by sheredizing?
Nuts, bolts or any fasteners rely on tension are tumble in the powdered zinc, the tem used is
sheredizing.
252. Name three types of paint feed for a conventional spray?
Suction Feed, Gravity feed & remote pressure pot.
253. What is calorising process?
Calorising is coating with aluminium, one way of calorising a component is to dip it into molten
aluminium.
254. What is the BS 2015 term for skipped or missed areas?
Holidays.
255. A colour has three properties, what are they?
Hue, Brightness & Saturation.
20

256. Why would be paint applied by hot spray?
When paint is heated it reduce in viscosity and cure or drying starts quicker and reduces the need for
solvent addition.
257. On an airless spray tip how are blockage cleared?
By turning the tip through 180o
, triggering to ground or a container to clear the blockage.
258. How is atomization achieved using conventional sprays?
Approximately 25mm in front of the aperture two channels blow air to converge at the paint stream.
At this convergence the paint is atomised into vary minute droplets and conduted onto the workpiece
259. How is atomisation achieved using airless sprays?
Atomisation occurs by forcing the paint at extremely high pressure usually 2000 to 2500 psi, through
a very small aperture 12 to 23 thou diameter into a volume of air offering resistance to paint flow as
the air & paint meet the paint atomized.
260. What is dip coating?
A component is dipped into a paint and hung to dry.
261. What do you understand from the term ropiness?
Brush marks.
262. What is efflorescence and how does it occur?
A whitish crystalline formation on bricks, mortar, plaster etc.
263. What is flocculation?
The development of loosely cohesive pigments agglomerates in coating material.
264. What could be the cause of bittiness in a paint film?
Inculsion of foreign matter or within paint itself.
265. What are the hazard signs for Toxic, very toxic, harmful and corrosive?
Black symbol of skull and crossbones on orange square for toxic, very toxic.
Black diagonal cross on an orange square for harmful.
Black symbol showing a tilted test tube dripping onto a hand for corrosive.
266. What is saponification?
The formation of a soap by the reaction of a fatty acid ester and an alkali?
267. What units are used for measuring toxicity?
PPM.
268. Which material would have to be used on a perpetually damp surface?
Moisture curing polyurethane.
269. What is padding?
Pads of mohair or foam are used to apply brush paint.
270. What causes lifting of a paint film?
Strong solvent over a coating using weak solvent.
22

271. Why would a paint inspector use potassium hexacyonoferrate?
To detect iron soluble salt.
272. What would be an average thickness for galvanizing?
100 um.
273. How can you tell the difference between blooming and chalking?
Blooming – under surface , chalking – over surface
274. What could be the reason for inter coat adhesive failure?
Oil , Grease etc.
275. Why are manufacturer developing solvent free, water borne and powders?
Environment protection act requirement.
276. How can bleeding be avoided?
By applying sealer first.
277. In less than 30 words explain the duties of a painting inspector?
Activities such as measuring, examining, testing, gauging, storage of materials, quality plan, site
plan and relevant local requirements.
278. What is meant by the term stripe coats?
Paint applied by brush to welds and edges.
279. How many cm3
are there in 4.5 litres?
4500 cm3
.
280. Name two types of mill & describe their work?
Direct charge mill and pre-mix mill.
Direct charge mill – which takes and mill all the raw ingredients together eg. Ball mill, attritor mill
& high speed dispenser.
Premix mill – Take the ingredients which have been premixed to a rough consistency and refine this
mixture to a high quality paint. This system is used for large production runs. Eg. Sand mill, colloid
mill, single row mill & triple row mill.
281. What is compliant coating ?
A coating which complies with the requirement of environment protection Act. 1990.
282. What is damp surface?
Surface on which water is not readily detectable but of which the temperature is below the dew
point.
283. What is fully weathered galvanizing?
A galvanized steel surface on which a cohesive oxide layer has formed by natural weathering. The
surface will normally be dull and lacking in metallic sheen.
284. What is hot duty surface ?
Metal surfaces on the assembly that will attain a temperature of 100o
C or above during use.
23

285. What is moist surface?
Surface from which standing water and droplets have been removed but on which there is a
noticeable film of water.
286. What is T-wash?
A non-proprietary material used as a primer or pretreatment for zinc metal surfaces.
287. What has to be considered for maintenance or repainting?
Based on a survey of the item or plant which would determine :
The existing paint system.
The extent of breakdown and corrosion.
The in service environment conditions.
The nature and extent of any surface contamination.
288. Why & What Equipment to be protected and masked before preparation and painting?
Prior to any cleaning, surface preparation or painting, the contractor shall protect and mask
equipment and areas in need of protection, with masking material. Eg. Fire protection equipment,
weld end preparation, lubrication paints and nameplates.
289. What is the name of the mill used to produce mastics, fillers and putties?
Tripple roll mill.
290. What special surface preparation are required for coating on concrete ?
Scrabbling.
291. Give the reason why different surface require different paint systems?
Painting always depends on the nature of surface (rusted, pitted, or new), type of surface (ferrous or
non-ferrous) condition (industrial or marine) cost, temp. etc.
292. What additional information would you record when maintenance painting a pipeline without
removing the previous coats?
What the existing painting is ?, The extent of breakdown and corrosion, the in service environmental
conditions, the nature and extent of any surface contamination.
293. If you worked on a contract where frequent stoppage occurred for poor weather, what
additional information would you record?
what the weather conditions were, how long stoppage lasted, progress of work to stoppage,
assessment of damage caused by weather to wet painted areas, loss of material due to stoppage.
294. Name an equipment used to test for opacity?
Pfund cryptometer, hiding power chart with applicator.
295. What is another name for a sand mill and describe its operation?
Pearl or bead mill, rotation disc attached with vertical shaft aid to shear as paint, slurry, forced
through steel ball which present between the disc. The degree of dispersion is high. Suitable for long
production run of popular paints.
24

296. Briefly state the preferred paints system ( and DFT) for new and maintenance painting at
works and site for above ground pipeline and plant installations?
High build aluminium primer - 75 um.
MIO - 75 um
High build epoxy - 75 um
Epoxy or polyurethane acrylic - 40 um
Total - 265 um
297. List ten duties of paint inspector ?
Learn the specification, get to know the plant, ensure all concerned understand the specification,
keep the engineer informed at all times of any departure from the specification, make written reports
at an agreed frequency, conduct and attend site meetings, before commencing the work, check
environment, equipment, materials, check previous days work, agree the day work programme with
contractor’s senior personnel. On the completion of the each stage, ensure that, system meets the
specification by carrying out witness tests and check for application faults. On completion of the
work, make the final check and the summary reports.
298. Describe contractors mall practice, which you are aware?
Use of unskilled labours, unsafe scaffolding, use of unsuitable equipment, leaking compressor,
brushes, damaged ladders, etc. Insufficient blasting or paint in difficult areas likes underneath of the
pipe etc. painting and preparing the surface during in inclement weather conditions, painting before
inspection of substrate or previous coats. Reusing of expandable abrasives, use wrong solvent or an
excessive solvent, use diesel in the paint as a solvent or plasticizer, use of incorrect paint or different
manufactures paint. Applying of low thickness etc.
299. What is the procedure to remove algae and mould growth?
Algae and mould growth shall be removed by scrubbing with stiff bristle brush, using clean water,
after the removal of a boicidal wash to be acceptable to prevent contamination of the new paint
system. All surfaces shall be dry before painting commences.
300. What particular problems relate to the splash zone?
Possibility of surface contamination (salt, water), damage (from service & work coats), mould and
algae growth high salt contamination, restricted areas etc.
25

Docfoc.com bgas question and answer

More Related Content

What's hot (20)

Viewers also liked (20)

Similar to Docfoc.com bgas question and answer (20)

Recently uploaded (20)

Docfoc.com bgas question and answer