vyv_cox
Well-known member
This subject comes up from time to tiime and I have posted a few times on it. This case history came up today in my company's internal communications. Thought it might answer some questions.
"As a result of condition monitoring of the protective coating system at two onshore gas plants in the Netherlands, coating damage and severe localized external corrosion has been observed and reported.
The reported severe corrosion and heavy material losses was striking because one of these plants is located in the east part of the Netherlands which may be considered as a very low corrosive environment.
An investigation has been carried out by an independent third party.
Although a surface cleanliness of SA 2, 5 was required prior to coating, the investigation of this third party shows remainders of mill scale on the steel surface and under the present coating system. This indicates that the steel work has not been properly blast cleaned during construction and most probably been cleaned by automatic blasting in the shop.
This case shows that comparison by visual inspection of surface cleanliness as has been specified in industrial standards such as ISO 8501-1, in particular for automatic shop blasting, was not effective enough to ensure a good quality surface cleaning. Good quality surface cleaning is required as the basis for long term corrosion protection.
For future blast cleaning operations, we shall specify requirements such as use of magnifying glasses, a ferroxyl test in accordance with ASTM-A380 etc., in addition to ISO 8501-1, to ensure the required surface cleanliness, in particular for shop blasted steel.
It should be noted that the costs for renovation of the protective coating system applied on steelwork showing remainders of mill scale will far exceed the costs required for normal maintenance because of the need to blast back to bare metal and fully recoat."
<hr width=100% size=1>
"As a result of condition monitoring of the protective coating system at two onshore gas plants in the Netherlands, coating damage and severe localized external corrosion has been observed and reported.
The reported severe corrosion and heavy material losses was striking because one of these plants is located in the east part of the Netherlands which may be considered as a very low corrosive environment.
An investigation has been carried out by an independent third party.
Although a surface cleanliness of SA 2, 5 was required prior to coating, the investigation of this third party shows remainders of mill scale on the steel surface and under the present coating system. This indicates that the steel work has not been properly blast cleaned during construction and most probably been cleaned by automatic blasting in the shop.
This case shows that comparison by visual inspection of surface cleanliness as has been specified in industrial standards such as ISO 8501-1, in particular for automatic shop blasting, was not effective enough to ensure a good quality surface cleaning. Good quality surface cleaning is required as the basis for long term corrosion protection.
For future blast cleaning operations, we shall specify requirements such as use of magnifying glasses, a ferroxyl test in accordance with ASTM-A380 etc., in addition to ISO 8501-1, to ensure the required surface cleanliness, in particular for shop blasted steel.
It should be noted that the costs for renovation of the protective coating system applied on steelwork showing remainders of mill scale will far exceed the costs required for normal maintenance because of the need to blast back to bare metal and fully recoat."
<hr width=100% size=1>
