End User Interview
• When the part arrives to the lab , any contents , or deposits inside are scraped out and preserved for chemical or microbiological examination .
• The sample is then subjected to non-destructive examination , mechanical property testing , macroscopic and microscopic examinations .
• Sample sections are identified for metallographic analysis .
Final interpretative stage
The second stage entails the analysis ; the engineers work with technicians and field personnel to establish potential causes for the failure . For example , gas pipelines most likely experience failure when water condenses allowing it to react with contaminants such as carbon dioxide or hydrogen sulfide to cause corrosion . Pipelines carrying liquids , such as crude oil , can experience internal corrosion when water or solids drop out . The analysis stage involves the following :
• The metallographic sections are mounted in an epoxy mould , polished and etched to help document microstructural features and the damage mechanism . Carbon steel requires different etchants compared to those used for stainless steel .
• Chemical and microbiological analyses , as required .
• Occasionally , materials are tested under simulated service conditions to gather information that may be otherwise not available .
• Once images and mechanical property databanks are collated , personnel begin creating a report and conclude relevant findings .
Corrosion Management : Prevention and Reduction
When looking at corrosion through the lens of metallurgy and material science , the focus is on the chemical reactions occurring on the metal leading to its oxidation . Within these chemical reactions , it is also important to consider the electrochemical reactions taking place as the metal begins to corrode . This in turn , helps determine corrosion rates which can be used to effectively monitor and control corrosion .
“ When stainless steel was invented , its original intention was for use in applications that required material that would not stain or rust . As stainless steel does not corrode the way carbon steel would , it was implemented across several industries . On the other hand , carbon steel corrosion is predictable enough to allow maintenance personnel to follow a scheduled routine . Stainless steel does not offer this predictability ,” said Dr . Mahajanam .
Stainless steels can undergo catastrophic cracking , which occurs without forewarning and can lead to disastrous consequences . Environmental factors often play a role for these cracking failures ; such as chlorides in marine environments , or the harsher conditions observed in the refining sector and chemical plants .
Metals and alloys are typically manufactured by extracting them from their oxide ores . Metal oxidation or corrosion is inevitable ; the job of operations personnel is to prevent or reduce this oxidization process . A large part of corrosion management is to ensure that corrosion occurs at a slower controllable rate , through use of stainless steels and other corrosion resistant alloys or controlling the service environment by adding chemicals or corrosion inhibitors to protect the asset ' s integrity .
Corrosion is an interdisciplinary subject that involves chemistry / electrochemistry , electrical engineering , and material science . Corrosion management is vital to most industries , and the research behind it is critical , especially for future engineers .
Current Projects
As an example of the benefit of failure analysis , Dr . Mahajanam discussed one of the most recent projects he worked on . “ The client provided us two sets of 304 stainless steel pipes that had leaked during hydrostatic testing . The 12-inch diameter pipe ran both above and underground , and had not yet been placed in service .. However , there were lapses in the project and standing water had been allowed to sit in the pipes for many months .”
For the above-ground pipe , the damage was observed on the body of the pipe , which is not a typical place for damage . The part of the pipe installed below ground had leaked at the welds , which is a common region for observing corrosion , damage , and failure . " After performing radiography to identify corrosion pits that had not broken through wall and analyzing them , my team and I concluded that the leaks occurred as result of internal microbiological corrosion . This damage is unique and can occur in 304 stainless steels . We utilized metallography , chemical analysis and microbiological testing to arrive at this conclusion .”
Microbiological damage had started on the inside surface of the pipe and made its way to the outside surface . Standing water inside the pipe in the month leading up to hydrotesting had allowed the microbes to eat into the metal . " We suggested using a biocide or inhibitor in the pipe , to repel the bugs and “ mothball ” the pipes prior to hydrostatic testing ." says Dr . Mahajanam .
Looking Forward
“ Corrosion management is a whole field of its own . There is metal that wants to corrode , and an environment that allows for corrosion . There is an anode , a cathode and an electrolyte , the three basic
PIPE , FITTINGS AND FLANGES
Leading the way with solutions for specialty alloy piping requirements .
legs that form the basis for corrosion , and the challenge is trying to control one of the legs in order to prevent corrosion . ”
Although he has a Ph . D ., Dr . Mahajanam ’ s most favoured aspect of the role is the commitment to on-going learning . " It is a two-way process . You read more and you get more passionate about it ; I think you need to have the passion for surviving in any industry . Stainless steel and its use in various applications are not going anywhere . There are still so many things to learn and discover given the vast number of alloys and materials ,” stated Dr . Mahajanam . “ An important part of this discipline is the number of core engineering jobs that will continue to become available . Corrosion is essentially extractive metallurgy in reverse , and I am truly excited to keep abreast of the innovations in corrosion prevention / protection ,” he concluded .
Determining Damage
For stainless steel materials , non-destructive damage examination involves a liquid penetrant test . If the sample is carbon steel , which is more often the case , either a magnetic particle inspection or wet fluorescent magnetic particle inspection is in order . “ Magnetic particle inspections induce magnetic fields to the component being tested . When the magnetic flux encounters a defect or crack , it is deflected . The particles are then attracted to the region containing the flux leakage , indicating the presence of the flaw and allowing personnel to identify its location in the sample ,” explained Dr . Mahajanam . “ Liquid or dye penetrant testing requires using a penetrant chemical applied directly to the region containing the failure . After a few minutes , the excess penetrant is removed and the developer is applied which helps bring out the indication or crack .” www . PAInc . com
Stainless Steel World Americas - August 2022 | www . ssw-americas . com 7