Critical Pitting Temperature (CPT) Testing
Ferric chloride immersion testing determining the critical pitting temperature at which the specimen begins to exhibit pitting attack, per ASTM G48 Method A or E depending on specimen and grade.
ASTM G48 Standard Method
Ferric Chloride Immersion Test
CPT / CCT Temperature Result
Quantitative Alloy Resistance Metric
Stainless & Duplex Grade Focus
Not a General Coating Screening Test
Chloride Service Qualification
Marine, Offshore & Process Environments
A Targeted Test for a Specific Corrosion Mechanism, Not a General Exposure Screen
Salt spray testing, which we also offer, is a general accelerated atmospheric exposure test primarily suited to evaluating coating corrosion protection — it rates hours to first visible corrosion under continuous salt fog exposure. ASTM G48 addresses a genuinely different question with a genuinely different method: rather than screening a coating's general corrosion resistance, it quantifies a specific alloy's inherent resistance to two localized, particularly aggressive corrosion mechanisms — pitting and crevice corrosion — that stainless and duplex stainless steel grades can be susceptible to in chloride-containing environments, especially where a low-oxygen crevice geometry (a gasket interface, a bolted joint, a threaded connection) exists. The test method immerses the specimen in a ferric chloride solution, a chemically aggressive environment specifically chosen because it reliably initiates pitting and crevice attack in susceptible alloys, and the result is reported as a specific temperature value — the critical pitting temperature (CPT) or critical crevice temperature (CCT) — the temperature at which the alloy specimen begins to exhibit measurable pitting or crevice attack under the test's standardized conditions. This is a quantitative alloy-performance metric directly comparable against a specification's minimum required CPT or CCT, distinct from salt spray's hours-to-corrosion coating rating, and it is specifically the test method used to verify that a given stainless or duplex grade's actual corrosion resistance in chloride service meets what its alloy designation promises, particularly relevant for materials destined for marine, offshore, or chloride-process environments.
Pitting & Crevice Corrosion Testing Services
Critical Crevice Temperature (CCT) Testing
Ferric chloride immersion testing with crevice-forming devices applied to the specimen, determining the critical crevice temperature at which crevice corrosion initiates under the test's standardized low-oxygen crevice geometry.
Duplex and Super-Duplex Stainless Grade Testing
G48 testing supporting duplex and super-duplex stainless steel grade qualification, verifying the alloy's actual pitting and crevice resistance meets the performance level its designation implies.
Weld and Heat-Affected Zone Testing
G48 testing extended to weld metal and heat-affected zone specimens, verifying that welding hasn't locally degraded the base material's pitting and crevice corrosion resistance.
Standards, Reporting and Application for G48 Testing
ASTM G48 Method Selection
Test method (A, B, C, D, or E per ASTM G48) selected based on specimen type and whether pitting or crevice resistance is the specific property being evaluated.
Weight Loss and Visual Attack Assessment
Post-test specimen evaluation combining visual examination for pitting or crevice attack with weight loss measurement, supporting the CPT or CCT determination per the standard's criteria.
PREN Correlation and Grade Verification
G48 results considered alongside a grade's calculated pitting resistance equivalent number (PREN) as part of confirming actual measured performance aligns with the alloy's expected chloride resistance.
Test Report Documentation
Complete test reports documenting method used, test temperature series, and determined CPT or CCT result, supporting material qualification and customer quality records.
A Targeted Test for a Specific Corrosion Mechanism, Not a General Exposure Screen
Stainless and duplex stainless steel grades derive much of their practical value from resistance to general corrosion, but general corrosion resistance and localized corrosion resistance are genuinely distinct properties, and a grade with excellent general corrosion performance can still be vulnerable to pitting or crevice attack under specific chloride-containing conditions — a meaningfully more insidious failure mode, since pitting and crevice corrosion concentrate material loss at small, localized sites rather than distributing it across a surface, and can progress to through-wall penetration while the surrounding material remains largely unaffected and the overall component appears superficially sound.
ASTM G48 exists specifically to quantify this localized corrosion resistance rather than screening general or coating-related corrosion behavior, which is precisely where it differs from a test like salt spray: the specimen is immersed in a ferric chloride solution, an environment chosen specifically because it reliably and aggressively initiates pitting and crevice attack in susceptible stainless alloys, and testing is performed across a series of temperatures to determine the specific critical temperature — critical pitting temperature (CPT) for general surface exposure, or critical crevice temperature (CCT) when an artificial crevice-forming device is attached to the specimen — at which that specific corrosion mechanism begins to occur under the test's standardized conditions.
The result this testing produces is a genuinely quantitative, alloy-specific performance metric, directly comparable against a specification's minimum required CPT or CCT value, in contrast to salt spray's hours-to-visible-corrosion rating which is oriented toward coating protection performance rather than base alloy localized corrosion resistance. This distinction matters practically because the failure mechanisms differ fundamentally: a coating failure exposes the underlying base metal to general corrosion, while pitting or crevice corrosion attacks the base alloy itself at specific vulnerable sites regardless of coating, meaning G48 testing addresses a performance question salt spray testing simply isn't designed to answer, and vice versa.
For customers specifying stainless or duplex stainless steel forgings for marine, offshore, or chloride-process service where localized corrosion resistance is a genuine performance requirement, Shivam Forge provides ASTM G48 pitting and crevice corrosion testing with full test report documentation. Contact our quality engineering team at +91-9265772827 or sales@shivamforge.com with your component and material specification to discuss scope and quotation.
Frequently Asked Questions
How is ASTM G48 different from salt spray testing?
Salt spray testing is a general accelerated atmospheric exposure test primarily used to rate coating corrosion protection performance in hours-to-corrosion terms. ASTM G48 is a targeted, quantitative test evaluating a specific alloy's inherent resistance to localized pitting and crevice corrosion using ferric chloride immersion, reporting a specific critical temperature result rather than an exposure-duration rating. The two tests answer genuinely different questions about genuinely different corrosion mechanisms.
What is the difference between critical pitting temperature and critical crevice temperature?
Critical pitting temperature (CPT) is the temperature at which general pitting attack initiates on an exposed specimen surface. Critical crevice temperature (CCT) is determined using a specimen with an artificial crevice-forming device attached, simulating the low-oxygen crevice geometry found at gasket interfaces or bolted joints, and is typically lower than CPT for a given alloy since crevice conditions are more aggressive to corrosion initiation than open surface exposure.
Which materials require G48 testing?
G48 testing is most commonly applied to austenitic stainless steel grades with enhanced chloride resistance claims, and to duplex and super-duplex stainless steel grades, particularly for components destined for marine, offshore, or chloride-containing process service where localized corrosion resistance is a genuine performance requirement rather than a nominal one.
Can you test weld areas, not just base material?
Yes. G48 testing can be performed on weld metal and heat-affected zone specimens specifically, verifying that welding hasn't locally reduced the base material's pitting and crevice corrosion resistance — a genuinely important check since welding thermal cycles can alter local microstructure in ways that affect corrosion performance.
What documentation do you provide for G48 testing?
Test reports documenting the method used, the test temperature series evaluated, and the determined critical pitting or crevice temperature result, supporting material qualification records and specification compliance documentation.
Why Choose Shivam Forge
Trusted forging manufacturer — Rajkot, Gujarat
Shivam Forge delivers precision hot-forged components from our integrated Shapar, Rajkot facility — covering forging, CNC machining, heat treatment, and quality inspection under one roof.
- Hot forging from quality alloy steel billets (42CrMo4, C45, EN8, SS316L)
- In-house CNC/VMC machining to drawing — ±0.05mm tolerances
- Heat treatment — normalizing, hardening, tempering, annealing
- CMM inspection and full EN 10204 3.1 material certification
- Custom OEM forging from customer drawings — PPAP/ISIR available
- Fast export from Mundra Port — CIF worldwide, FOB India
- Export expertise — Europe, Middle East, Americas, Asia-Pacific