Corrosion Engineering

14. Design and Evaluation of Paints and Coatings in Dhahran-Dammam Area

(Typical of Sea-Coastal Environment)

Objective	The factors affecting the design are shown in the objective tree. One critical factor in designing is the environment to which the coating would be subjected.
Climatic Data	Information on climatic data is important in designing a coating system.
	The following parameters are included in the climatic data.
	Dry bulb temperature Humidity Wind speed Average rainfall Pollution Summary of climatic data of Dhahran Average dry bulb temperature, maximum. 44.29⁰ C, minimum 22.80⁰ C Average relative humidity, maximum. 82.24%, minimum 18.4% Average wind speed 4 m/sec The above average is for the month of August which is one of the hottest and humid month, the average is base on ten years data)

Coating Selection	A coating suitable for Dhahran typical of sea coastal environment was to be selected and evaluated.
Sample Preparation	Six samples of size 21 cms (L), 11 cms (W) were prepared. Two diagonal scratches were made on the samples.
Sample Selection	The following samples were selected.
	Sample # 1: A sample coated with solvent free amine cured epoxy.
		1^st coat: 7785 SIGMAGUARD CSF 85 300 MIC Appearance: Light blue
	Sample # 2: A two layer coating comprising of high build polyamine adduct cured coal tar epoxy coating ( both layer with same constituents).
		1^st coat: 7472 SIGMA TCN 300 150 MIC 2^nd coat: 7472 SIGMA TCN 300 150 MIC Appearance: Black
	Sample #3: A three layer coating of polyamide cured epoxy primer.
		1^st coat: 7413 SIGMA COVER PRIMER 150 MIC 2^nd coat: 7682 SIGMA CAP COATING EP 125 MIC 3^rd coat: 7690 SIGMA CAP FINISHES PU 75 MIC Appearance: Milky White
	Sample # 4: A three layer coating comprising of polyamide cured epoxy primer.
		1^st coat: 7413 SIGMA COVER PRIMER 75 MIC 2nd coat: 7682 SIGMA CAP COATING EP 125 MIC 3^rd coat: 7690 SIGMA CAP COATING EP 100 MIC Appearance: White
	Sample # 5: A three layer coating with high build amine adduct cured phenolic epoxy primer.
		1^st coat: 7409 SIGMA PHEGUARD PRIMER 100 MIC 2nd coat: 7435 SIGMA PHENGUARD COATING EP 100 MIC 3^rd coat: 7436 SIGMA PHENGUARD FINISH 100 MIC Appearance: Grey
	Sample # 6: A three layer coating based on modified alkyd resin and pigmented with red oxide.
		1^st coat: 0809 SIGMA REDOXIDE QC 35 MIC 2nd coat: 0811 SIGMA COLOR UNDEROCAT 35 MIC 3^rd coat: 0818 SIGMA COLOR GLOSS 35 MIC Appearance: Pink
Sample Evaluation	All samples were evaluated for their resistance to corrosion in a salt spray cabinet. The arrangements of the samples are shown below.
Experimental Parameters	Experimental parameters according to specification B 117-97 (ASTM)
Apparatus	Salt spray (fog) equipment containing a 3.5 wt% salt solution reservoir, compressed air, atomizing nozzle, specimen supports, provision for heating.
Support	The specimen were placed on supports so as not to contact any metallic surface and allowing free settling of fog.
pH, Temperature and Exposure	The pH of the solution was maintained in the range 6.5 -7.0, the temperature in the chamber was maintained at 35^o C + 1.1-1.5^oC. All specimens were exposed for one week.
Inspection Results	Based on the visual inspection and the metallographic examination the extent of rust which developed was assessed.
Conclusion	As shown in the following figures, the best resistance was offered by Sample # 3 (three layered polyamide coating) followed by Sample # 2 ( high build polyamide adduct cured coal tar epoxy coating).