Screening Tests for Corrosion Inhibitors
By Joseph Itodo Emmanuel
Meet the Author
Dr. Joseph Itodo Emmanuel
Joseph Itodo Emmanuel is a corrosion specialist with core expertise in corrosion and integrity management in the upstream, mid-stream and downstream sectors of the oil and gas industry.
He is Chartered Engineer registered as a European Engineer with FEANI (Europe), 
and also a Fellow with Institute of Corrosion (UK).
Joseph obtained his Bachelors in Chemical Engineering from FUT Minna, Nigeria, Masters in Science (MSc) from Heriot-Watt University, Edinburgh, UK, Masters in Business Administration (MBA) from University of South Wales, UK and Postgraduate Certificate in Education (International) from Liverpool John Moore’s University, Liverpool, UK. He is a certified Corrosion Specialist, Chemical Treatment Specialist and Cathodic Protection Specialist. and also a member of SPE (USA), AMPP USA), EI (UK), IET (UK), COREN (NIG), NSChE (NIG), COREN (NIG) and NSBE (USA).
Joseph is a trainer, scholar, mentor, STEM facilitator, and author of books and peer 
reviewed journal publications to his credit.
- How do we best screen for Corrosion Inhibitors?
There has been a growing call by stakeholders in academia, industry, and government for a switch from conventional chemical inhibitors due to their high toxicity and harmful impact on human, environment, and aquatic life to organic green corrosion inhibitors (OGCI) developed from nanomaterials and plant extracts through green synthesis. The preference for OGCI developed from nanomaterials and plant extracts has led to renewed global interest, with a focus on sourcing OGCI materials from plant extracts. OGCI from plant extracts have strong adsorption, eco-friendliness, non-toxicity, non-bioaccumulation, biodegradability, extraction ease, availability, and cost effectiveness.
Laboratory Screening Test for Candidates OGCI
After the initial laboratory static testing of the proposed candidate OGCIs, those with good performance (high efficiencies) above 80% are then subjected to a four-phase test programme. These tests are aimed at ensuring the candidate OGCI meets the stringent industry requirements by functioning with similar efficiencies under field-simulated conditions.
- 
The first phase involves the testing of the physical and chemical properties of the candidates OGCI and a robust verification process by assessing the quality assurance and control (QA/QC) parameters.
- 
The second phase, involves bubble tests at near-field operating temperatures and pressures to screen the performance of OGCI for field application before field trials. The test temperatures can vary between 37 to 40 oC (this is a very low temperature range v industrial applications), and the test pressure is simulated to be close to the operating pressure of the pipeline to be inhibited and for OGCI to be deployed for sub-surface facilities, higher test bubble pressures and temperatures are technically recommended considering the higher operating temperature downhole and the need to simulate near-field conditions. These tests can be conducted in the brine phase or in a in a crude oil and brine mixture. The bubble test can also be divided into three subsets: the first simulating a sweet corrosion environment using carbon (IV) oxide (CO2), the second simulating a sour conditionusing hydrogen sulphide (H2S), and the third simulating a sweet and sour condition using a mix of carbon (IV) oxide (CO2) and hydrogen sulphide (H2S).
- 
The third phase involves conducting a dynamic test using a rotating cylinder electrode (RCE) to replicate (duplicate) the real-field operating pressure, temperature, and flow effects. During this phase, if the candidate inhibitor is tested for gas systems and not oil or water systems, it is also tested for the likelihood of hydrogen-induced cracking (HIC).
- 
During the fourth phase, the OGCI candidates are subjected to a supplementary test, viz., a pitting test, to confirm the presence or absence of pitting using test coupons (strip coupons).
Field Trial for Candidates OGCI
After the candidates OGCI have passed the laboratory screening test, they are further subjected to laboratory field trials as a final test to determine OGCI efficiency in the live system and to assess and evaluate secondary effects, viz., compatibility, physical (fouling), and functionality with other oilfield chemicals, process fluids, chemical injection pump parts, and materials (seals, etc.).
The effects of the dosed OGCI further downstream from the injection location include the likelihood of forming emulsions, the secondary effects of oil on the quality of the produced water, the stability of the formed foams, and general effects on people and the environment in the event that the product is accidentally discharged or spilled. In addition, a range of process stream parameters should be considered as they have effects on the corrosivity of the test system, viz., operating pressure, operating temperature, water cut, flow rate (flow regime), CO2, H2S, dissolved oxygen, organic acids, free sulphur, SRB (bacteria), water chemistry, organic acids, scaling tendency, total dissolved acids, pH, and gas oil ratio (GOR) (59, 60). The four most commonly used laboratory methodologies and standards for evaluating corrosion inhibitors in general for oilfield and refinery applications are presented in Table 1 on the next page.
Secondary Effects Associated with Testing OGCI
During the field trial of the screened OGCI, the secondary effects are closely monitored by implementing the required procedures, checks and test protocol to ensure OGCI is compatible with system fluids at recommended injection rate (dose rate), water cuts, other production chemicals (emulsifier, oxygen scavengers, flow assurance chemicals, biocides etc.), storage and pump materials, wetted materials within the system, and process stream. The secondary effects, performance check and test protocol carried out are summarised in Table 2 below.
Prospects, and Challenges
Empirical studies have revealed good inhibition efficiency for OGCI developed from nano sized plant extracts and nanomaterials. However, the reported inhibition efficiency from gravity (weight loss) and electrochemical methods would not qualify when subjected to stringent industrial screening tests, viz., kettle (bubble) tests, rotating cylinder electrode (RCE) tests or cylinder electrode rotating cages, jet impingement, high-pressure loop tests, wheel tests, localised corrosion tests, and autoclave tests. To validate the reported performance data, the same product should be tested under industrial conditions. In addition, there is the need for the chemical and physical properties of the developed OGCI to be further investigated under field operating conditions to evaluate their solubility in produced fluid, their emulsion forming tendency, their foaming characteristics, thermal and hydraulic (pressure stability), compatibility, film persistence in in-service conditions, and optimum protection at optimum inhibition efficiency. Also, more studies of OGCI made from nano sized plant material extracts and nanomaterials need to be undertaken to investigate the complex corrosion inhibition mechanism of plants-based extracts on carbon steels and other alloys.
Table 1:Laboratory Methodologies Standards for Evaluating Corrosion Inhibitors.
Table 2: Secondary Effects, Performance Check and Test Protocol.
