4 Jan 2022
Avoid Substrate Contamination Inspection Failures by Switching to RZG Hard Rock Garnet Abrasives
The link between premature coatings failure and non-visible soluble salt contamination after blasting is well known. If salts remain on the surface after cleaning, they can attract moisture that can permeate the coating and may result in formation of blisters (osmotic blistering) as the water vapour finds its way to the salt crystals. Salts may also accelerate the corrosion reaction and the formation of under film corrosion.
You cannot see this contamination – you can only test for it.
The industry standard for testing residual salt contamination after blasting is according to ISO 8502-6 (Bresle patch method) and ISO 8502-9 (water-soluble salts by conductivity). The maximum accepted level of salt contamination is typically 20 mg/ m2 for new fabrication, and from 35-50 mg/ m2 for maintenance.
Furthermore, the generally accepted method for testing abrasive soluble salt contamination is according to method ASTM D4940 (Test for Abrasive Contamination Standard Test Method for Conductimetric Analysis of Water Soluble Ionic Contamination of Blast Cleaning Abrasives), and the typical maximum in the oil and gas industry is set at 150 µS/cm.
The International Association of Oil and Gas Producers (IOGP) Joint Industry Program (JIP33), Standardised Procurement Specifications calls out as follows:
- Less than 150µS/cm abrasive soluble salt contamination (ASTM D4940); and
- Less than 20 mg/ m2 substrate contamination (ISO 8502-6 and 8502-9).
IOGP members include Aramco, ADNOC, PETRONAS, ExxonMobil, Shell, Chevron, Qatar Gas, in total 78 members.
RZG hard rock garnet abrasives naturally contain soluble salt contamination well below the standard, certainly less than 100µS/cm, and often in the range of 75-85 µS/cm. Unlike alluvial ‘beach garnet’, RZG hard rock garnet were never exposed to exceptionally high chloride contamination from the sea.
Accordingly, after blasting with RZG hard rock garnet abrasives, the typical Bresle result is less than 20 mg/ m2, whereas the Bresle result after using alluvial ‘beach garnet’ is typically twice that.
Take the stress out of complying with the very strict residual sat contamination specifications – by switching across to RZG’s line of high quality hard rock garnet abrasives.