ASTM G48 Pitting & Crevice Corrosion

Scope

ASTM G48 covers the evaluation of pitting and crevice corrosion resistance of stainless steels and related alloys by exposure to ferric chloride solution. The standard provides several methods to address different objectives:

• Method A – ferric chloride pitting test, evaluating resistance to pitting by mass loss and pit examination after exposure
• Method B – ferric chloride crevice test, using a crevice-forming device to evaluate crevice corrosion resistance
• Methods C and D – determination of the critical pitting temperature (CPT) and critical crevice temperature (CCT), the minimum temperatures at which pitting or crevice attack initiates
• Methods E and F – additional procedures for critical temperature determination on specific product forms
• Evaluation basis – mass loss, presence and depth of pits, crevice attack, and/or critical temperature, depending on the method
• Applicable materials – stainless steels, duplex and super-duplex stainless steels, nickel-based alloys, and related alloys (including welds)
• Test environment – acidified ferric chloride solution under controlled temperature and exposure time

Applications

• Stainless steel and alloy ranking – comparing the localized corrosion resistance of different stainless steels and nickel alloys to support material selection for chloride environments
• Duplex and super-duplex stainless steel qualification – confirming the pitting/crevice resistance of duplex grades, which are widely used precisely for their localized corrosion resistance
• Weldment qualification – evaluating welds and heat-affected zones, where the localized corrosion resistance is often lower than the base metal, a common concern in fabricated stainless components
• Oil and gas / marine / chemical processing – qualifying alloys for service in chloride-rich environments where pitting and crevice corrosion are primary degradation risks
• Material acceptance testing – verifying that a heat or product form meets a specified pitting/crevice resistance requirement (often referenced via critical pitting/crevice temperature)
• Process and metallurgical verification – confirming that processing (such as solution annealing of duplex stainless steel) achieved the intended corrosion resistance
• Failure investigation – assessing whether inadequate localized corrosion resistance contributed to a pitting or crevice corrosion failure

Benefits

• Directly evaluates localized corrosion, the real risk for stainless – uniform corrosion is rarely what fails stainless steel in chloride service; pitting and crevice attack are, and G48 targets exactly these mechanisms
• Aggressive ferric chloride gives a discriminating challenge – the severe test environment effectively separates alloys by their localized corrosion resistance, making it a strong tool for ranking and qualification
• Critical temperature methods give a comparative ranking number – CPT and CCT provide a single comparative temperature that ranks alloys and is widely used in material specifications
• Reveals weldment weaknesses – because it can test welds and heat-affected zones, G48 catches cases where fabrication has reduced the localized corrosion resistance below that of the base metal
• Widely recognized for specification and acceptance – as a standard, well-established corrosion test, G48 results are accepted across the metals supply chain for material qualification in chloride environments