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INSPECTION LOGBOOK

Coating Inspections - Inspection of Steel Surface Preparation, Part 1 Massimo Cornago NACE International Certified Coating Inspector, NACE CIP PEER Reviewer

I

cornago@ipcm.it

n our previous article, “Basic Inspection Practice”1, we analysed

1. Soluble salt contamination

the responsibilities of a Certified Coating Inspector (CI) during the

The CI must check that the surface is free from contamination to

preliminary inspection phase (Preliminary Inspection Responsibilities,

the extent specified, especially in terms of chlorides, sulphates,

paragraph 1), with ample space devoted to the necessary work

iron ions, and dust. Chloride salt contamination, in particular, can

planning activities. We will now delve into the inspections to

be tied to different sources, such as airborne industrial chemicals,

be carried out during the surface preparation phase (Surface

salt contained in a marine atmosphere (in areas near or on the

Preparation Inspection, paragraph 2), particularly those relating to

sea), direct contact with sea water, defrosting of bridges and/or

surface contamination. Although often project specifications do not

highways on which salt has been thrown to prevent freezing, or

mention this, it is good practice that, during the pre-job meeting, the

even already contaminated abrasives. The latter are often invisible

CI requires two steps to be carried out. These include contaminant

to an inexperienced eye and they are generally not removable by

removal, as contaminating agents can affect the adhesion of coatings

abrasive blast cleaning.

thus leading to the system’s premature failure due to corrosion, and

Although exact standards of acceptability have not been established

the achievement of proper roughness of the metal surface to be

in terms of allowable amounts of contamination that may remain

treated, in order to guarantee good adhesion.

and not affect coating performance – of course, each paint product

There are many ways to obtain proper surface preparation, including

has a specific value – there are some “conventional” parameters of

solvent cleaning, water cleaning, hand tool cleaning, power tool

reference for both new construction and maintenance works. In

cleaning, abrasive blast cleaning, and centrifugal blast cleaning;

general, research and experience show that removing any chemical

all the inspection procedures required for each of these methods

contamination helps extend the service life of coatings over time.

are governed by international standards, such as NACE, SSPC, ISO,

The standard NACE5/SSPC-SP12 is a valid help for this purpose. In

etc. Surface preparation is preceded by a control phase on the

fact, it is almost always mentioned in project specifications as the

surface itself (steel preparation). Here, the CI assesses all aspects

official reference document. Alternatively, a specifier drawing on

of the metal surface to be prepared to coating, including welding,

personal experience and/ or the support of the paint manufacturer

cutting, grinding of welds and sharps edges, weld spatters, etc., in

can give some directions and decide which are the minimum values

compliance with the reference standard regulations. Moreover, in

of acceptability.

case chemicals are used, which are generally very alkaline and/or

With the exception of acid/basic contaminants, which can be easily

contain thickeners, before surface preparation the CI must check

identified by measuring the surface pH, all other contaminants can

that the operation is carried out in full compliance with the project

only be determined through extraction, by swabbing or deionised

specifications and, above all, with the instructions issued by the

water-based cleaning with an aqueous solution. The latter can be

paint manufacturer. Indeed, if they are not properly removed, these

then analysed with different certified methods, such as indicator

products will remain on the surfaces long enough to alkalise and

strips (ASTM-D4262), conductivity meters, or other tools that can

attack the coatings.

determine a sample’s chloride ion content.

We will now describe in detail the tests to be carried out before the

The standard NACE5/SSPC-SP12 includes a table defining three

surface preparation phase.

levels of soluble salt contamination: 1. SC-1 – Surface free of all detectable levels of contaminants

M. Cornago, Coating Inspections – Basic Inspection Practice, in ipcm® Protective Coatings no. 35 (October 2020), pages 40-41.

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40

N.36 - 2020 DECEMBER - ipcm® Protective Coatings

(water-soluble chlorides, iron-soluble salts, and sulphates), as determined using available field test equipment.

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ipcm® Protective Coatings n. 36 - December 2020  

Read the latest edition of the magazine dedicated to corrosion prevention and control technologies in the heavy industry.

ipcm® Protective Coatings n. 36 - December 2020  

Read the latest edition of the magazine dedicated to corrosion prevention and control technologies in the heavy industry.

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