A leak or a rupture is the end of the story. The corrosion morphology — pitting, crevice, galvanic, microbial — tells you how it began and who is responsible.
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Corrosion rarely proceeds evenly, and that is what makes it a forensic problem rather than just a maintenance one. A pipe wall that thins uniformly at a predictable rate is a design and inspection question; a pit that penetrates the same wall in a fraction of the time is usually the result of a specific, identifiable local condition — a coating holiday, a stagnant crevice, a biofilm, a dissimilar-metal connection, or a process upset that changed the chemistry at one spot. The morphology of the attack is diagnostic: pit shape and distribution, crevice geometry, corrosion-product composition, and the presence of tubercles or biofilm each point toward a specific mechanism and, often, toward whoever specified the material, the coating, or the water treatment.
Corrosion is electrochemical, but the mechanisms that turn a passive surface into a leak differ enough in their evidence to be told apart.
Localized breakdown of a passive film — often chloride-driven — creating a self-accelerating occluded cell that acidifies and penetrates rapidly at a single point.
Oxygen depletion under gaskets, deposits, or lap joints creating the same acidifying occluded-cell chemistry as pitting, but governed by geometry rather than surface condition.
Dissimilar metals in electrical contact within an electrolyte driving accelerated attack on the less noble metal, concentrated near the junction.
Flow turbulence, impingement, or bubble collapse stripping the protective film faster than it can re-form, concentrating loss at elbows, tees, and orifices.
Biofilms and sulfate-reducing bacteria creating localized under-deposit chemistry that drives aggressive, often tuberculated pitting.
Broadly distributed metal loss from an aggressive environment or a failed coating or lining, thinning the wall toward a predictable end of life.
Corrosion investigations combine the physical morphology of the attack with the chemistry that produced it.
Localized corrosion rarely announces itself until it has already gone through the wall:
Pit morphology, corrosion products, and deposits are the evidence. Cleaning, sandblasting, or re-coating a failed section before it is documented and sampled destroys what identifies the mechanism.
MIC typically produces characteristic tuberculated deposits over the pits, and the corrosion products and biofilm beneath them have a distinct chemical and biological signature — sulfide-rich corrosion products under sulfate-reducing bacteria activity, for example. We sample the deposit and the pit interior separately, examine them under SEM/EDS, and where warranted test for microbial activity. Pit shape alone is rarely enough to make the call; the deposit chemistry usually is.
Yes, in most cases. A coating or lining failure typically shows localized attack concentrated at a specific holiday, disbondment, or damaged area, with the surrounding coated surface undamaged. Attack distributed broadly regardless of coating condition points more toward the environment or the coating specification itself being inadequate for the service. Cross-sectioning through the coating at the corrosion site is usually decisive.
Within limits, yes. Pit depth combined with the known or estimated exposure time gives an average penetration rate, and that rate can be compared against published corrosion-rate data for the alloy and environment to judge whether it is consistent with normal service or an upset condition. Layered corrosion products and any available inspection history — prior thickness surveys, in particular — sharpen the estimate considerably.
Because remaining-life and fitness-for-service calculations built on average wall thickness can dramatically overstate the safety margin at a pit or crevice that has penetrated far faster than the surrounding metal. A vessel can have generous average remaining wall and still be one pit away from a through-wall leak. API 570 and API 579 fitness-for-service assessments are built around this distinction for a reason.
The corroded section itself, with corrosion products and deposits left undisturbed and, ideally, stabilized to prevent further oxidation before analysis. Preserve any coating or lining remnants, samples of the process fluid or surrounding soil/water, and the inspection and maintenance history. Photograph everything in place before any cutting, cleaning, or sampling.
Technical briefings from our work in this area.
In a corrosion failure the scale and deposits are not debris covering the evidence. They are the evidence. Blasting, brushing or acid descaling before examination removes the record of the mechanism.
readGalvanic couples, area ratios, coating breaches, deposits and biofilms all accelerate corrosion locally. Each points at a different decision — material selection, coating spec, or how the asset was run.
readGeneral corrosion is an allowance and inspection question. Pitting and crevice attack perforate a wall the average calls healthy — and the two are measured, rated and reported by different rules.
readTell us what you are seeing. We will triage it and connect you with the right expert — usually within one business day.