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    Created on SEPTEMBER 2002

    Quiz no 1

1. list 5 duties of a paint inspector.

    ; To conform and secure that corrosion protection by protective coatings are carried out according

    to the specification and relevant standards;

    ; To check and observe;

    ; To monitor;

    ; To report;

    ; To act safety and keep up with developments within the field of corrosion;

    ; Generally to carry out all duties specified in the contract or specification.

    2. what is the difference between steel preparation and surface preparation?

    ; Steel preparation = comprise all necessary works in order to remove all steel structure defects:

    laminations; pittings; sharp edges; slags; welds defects (pores, undercuts) prior to surface


    ; Surface preparation = comprise all necessary methods, mechanical or by hand, to obtain a sound

    area to apply paints on.

    3. various types of surface contamination are frequently found on

     surface to be painted.

    A. Please list a minimum five of these types of contamination.

    ; Oil/grease; mill scale;rust;old paint and water soluble substances. B. How would you check a surface to be blasted in order to determine if The surface is contaminated with oil?

    ; By “water on the goose” method which consist in sprinkling

    Water on the surface suspected and if water forms small droplets

    It is highly certain that is contaminated with oil.

4. an abrasive blast cleaned steel surface to be immersed in sea water is contaminated with sodium chloride

    in excess of 200 mg/sqm. The surface is overcoated with an epoxy mastic system (3x100 mic). Upon

    immersion in water, blistering will start after a period of time. A. Would you assume that the size of the blisters would be greater in fresh water than sea water, or would

    you assume the opposite? Please state your reasons?

    ; The size of blistering will be greater due to the fact that fresh water has low salt content and in time will permeates the lining system placed in immersion and will disolve the nacl forming a solution with high salt to water ratio.the high the purity of the water the greater the tendency for osmotic blistering .this difference in salt concentration leads to what is called “osmotic driving force” which increases the rate of water permeation from bulk liquid side to the entrapped solution side in order to create an equilibrium accomplished when sufficient moisture from the bulk side permeates the lining system such that the salt concentration on either side of lining system (semipermeable membrane) is equalised. In practice, this never occurs due to the rapid drop off of osmotic driving force after innitial permeation occurs and the inelasticity of the lining material.

    B. What do we call this type of blistering?

    ; Osmotic blistering.

    5. blasting abrasives are commonly classified in four main groups. A. Please name at least three of these four main classification groups.

    ; Minerals-natural;

    ; Minerals-artificial;

    ; Metallic;

    ; Organic.

    B. Please name at least two examples of abrasives from each of the classification groups listed under a.


    ; Sands=silica ;garnet; olivine

    ; Slags = copper; iron; aluminium;silicon carbides;

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    Created on SEPTEMBER 2002

    ; Steel = grit ; shots; wire chops; bronze shots;

    ; Nylon pearls; polyestirene; coconut or walnut shells (ground).

    6. blasting abrasives may sometimes be contaminated, and the two most common contaminants are oil/fat and sodium chloride. Please describe the procedure for checking blasting abrasives for determination of contamination with:

    A. Oil/fats.

    ; Using some of the facilities listed below and visualizing the changes into solution. B. Water soluble salts.

    ; It is a mandatory procedure for testing the abrasives and must be carried out both in nb or m&r before

    blasting commence.for the test to be performed it needs the following: a conductivity meter;two glasses or

    plastic beakers (1=400 ml and 1=100 ml); a gradueted measuring cylinder of 250 ml; a supply of distilled

    water with conductivity of less than 2 ms/cm-1; a supply of calibration solution, consisting of 0.5 grammes of

    nacl in 1000 ml of distilled water maded in laborratory;rubber gloves; stirring rod; a funnel; filter papers;

    plastic bags; a stop watch; quantab chloride test papers ( to verifythat the high reading, when the abrasive test

    sample exceeds 300 ms/cm-1,is caused mainly by nacl rather than sodium sulphate. It will measure only the

    nacl) 1. fill the graduated measuring cylinder with 200 mg of abrasive sample and transfer into 400ml

    beaker; 2.fill the same cylinder with 200 ml distilled water and transfer to the 400 ml beaker; 3.stirr the

    abrasive and water with the rod one minute and allow the mixture to stand for eight minutes and stir again for

    one minute.these ten minutes are very important because it ensures the soluble salts have time to dissolve; 4.

    filter the liquid into the 100 ml beaker through the funnel discarding the first 10 ml. 50 ml should be collected

    for the test; 5. to take the conductivity reading immerse the probe in the test solution and note the reading

    displayed.the gage should be adjusted in the mode of microsiemens per centimetre. Less than 50 ms/cm-1 =

    accepted; less than 150 = accepted; less than 300 =acceptable but should be tested with quantab chloride

    paper; more than 300 = rejected without using any further testing. More than 2.8 units=rejected less than 2.8


     the compressed air used for blasting may also be contaminated with oil and or water. C. Please describe the method by which the compressed air may be checked for content of oil or water.

    ; Performing the blotter test. For one minute a white blotter or cloth is held withiin 60 cm of the end

    of an operating air line. If will be observed dark spots or condensation means that the oil/water is

    carried in the blasting air. And oil/moisture trap should be installed at the output line.

    7. abrasive blast cleaning of steel surfaces are carried out in accordance to internationally accepted standards. Please name (by designation and number) the standards used for:

    A. Determination of metal cleanliness

    ; Nace = no1 (white metal); no2 (near white metal); no3 (commercial).

    ; Iso 8501-1 = sa 3 ; sa2 ? ; sa 2.

    ; Sspc = sspc 5; sspc 10; sspc 6.

    B. Determination of metal roughness

    ; Iso 8503 -1. roughness comparators.choose comparator according to abrasive type. G = grit; s =

    shots and place the comparator on the steel surface and observe through the center hole.take the

    readings. Ry = fine(25-50 mic) segm 1-2 ;medium (50-85 mic) segm 2-3 and coarse(85-130mic)

    segm 3-4.

    8. various types of abrasives are used for different purposes. Name the abrasive types most suited for: A. Blast cleaning of stainless steel

    ; Garnet = non-metallic and organic = tomoid metal dust

    B. Centrifugal blast cleaning of steel profiles.

    ; Steel shots; steel grit; steel wire chops.

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Created on SEPTEMBER 2002

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