This is the most common protective measure applied to equipment susceptible to PTA SCC.
This method involves keeping the system free of moisture and oxygen.
Indirect Inspection
“Before standards like SP0170 existed, we saw unexplained cracking in units that had just come offline for maintenance,” says a senior metallurgical consultant. “It was counterintuitive. The equipment was fine while running, but broke while sitting still.”
) is often added to the wash to minimize the risk of chloride stress corrosion cracking, which can be triggered by standard wash water. nace sp0170 pdf 2021
As equipment ages and operating conditions become more severe, the 2021 update—often referenced via the AMPP (Association for Materials Protection and Performance) store—maintains crucial, updated guidelines for mitigating this silent killer of refinery equipment.
: Maintaining a dry air environment to prevent the liquid water formation necessary for PTA to develop. ANSI Webstore Standard Structure General scope and application Selection of materials and fabrication practices Dry nitrogen purging to exclude oxygen Alkaline washing of equipment surfaces Use of dry air to prevent water formation Special considerations for reactors Appendix A Background information on the PTA SCC mechanism Accessing the PDF As NACE is now part of This is the most common protective measure applied
If the vessel must be opened to the air for maintenance or internal inspection, the internal surfaces must be treated with an alkaline solution before oxygen can react with the sulfides.
Before the equipment cools down completely, it is purged with dry air or nitrogen. “It was counterintuitive