Graham Nelson and Andrew MacDonald, Clariant Oil Services
Use of chemical inhibitors is an effective method of corrosion control in the oil and gas industry. As well as corrosion inhibitor performance, a number of additional parameters such as emulsion tendency, foaming tendency and environmental profile are important.
Meeting and exceeding evolving and ever-more-stringent environmental regulations continues to be a challenge for chemical service companies. Historically, there has often been a reduction in performance when the corrosion inhibitor bases have been “greened” by the introduction of more biodegradable components. The challenge has been to develop products that provide high biodegradability and low toxicity but also provide corrosion inhibition performance comparable to traditional inhibitors.
All countries providing operating licenses in the North Sea (the UK, Norway, Denmark and the Netherlands) have regulatory bodies that demand environmental testing and registration of all production chemicals used offshore, including corrosion inhibitors. A number of tests must be performed on the inhibitor raw materials to evaluate biodegradability, toxicity and bioaccumulation. However, the regulatory bodies have different interpretations of the test results and, therefore, different ranking tools. Development of new products must take into consideration legislative controls from all the countries to ensure that products have wide application opportunities. In addition to governmental regulations, operators may have their own requirements for products.
Another major area of focus with all new and existing chemicals is the European Commission’s REACH (registration, evaluation, authorization and restriction of chemicals) regulation. The main aims of the regulation are protection of human health and of the environment from the risks that can be posed by chemicals, promotion of alternative test methods, free circulation of substances on the internal market, and enhancing competitiveness and innovation.
The regulation makes industries responsible for assessing and managing the risks posed by chemicals and for providing appropriate safety information to their users. The regulation affects all substances introduced to the EU market as such or in preparation. Non-EU companies are also affected when exporting substances or preparations to the EU or when buying chemicals from distributors sourcing in the EU. Clariant supports the targets and implementation of the regulation.
This article describes the development of new, environmentally-friendly corrosion inhibitors formulated with a novel amino acid corrosion inhibitor base. These new products have been extensively evaluated and have demonstrated comparable performance to a previous-generation environmentally acceptable product and to an established product successfully used for more than 17 years in the North Sea.
MATERIALS AND METHODS
Four chemicals were evaluated in the study. Two products (A and B) are classed as Gold with no substitution warning and as Yellow under UK/Dutch and Norwegian/Danish regulations, respectively, based on the countries’ current regulations. A third product tested for comparison (C) is classed Red under Norwegian/Danish regulations and Gold with substitution warning under UK/Dutch regulations. This product represents a previous generation of “green” corrosion inhibitors that only recently received a substitution warning due to changes in the UK regulations. The fourth product tested (D) is a traditional corrosion inhibitor formulation that has been in use in the North Sea for more than 17 years. The product is classed as Red in Norway and Silver with substitution warning in the UK. In addition, according to a North Sea operator internal classification, Products A and B will be classified Yellow (Y1) and Yellow (no Y classification), respectively. Product B represents the best categorization possible for complex blends under this system.
PERFORMANCE EVALUATION
The corrosion inhibitor packages were evaluated using a number of electrochemical laboratory performance tests: aqueous linear polarization resistance (LPR), partitioned LPR, pre-partitioned high-shear rotating cylinder electrode (RCE) and pre-partitioned weld tests. Tests were performed at about 80°C with all products being dosed at 50 ppm. Partitioning tests were carried out with a 50/50 (water/oil) pre-partitioning ratio.
Aqueous LPR testing. The LPR method is frequently used to screen and rank corrosion inhibitors. For this evaluation, brine-only tests were performed initially to assess the general performance of all the inhibitors. Results show that the new, environmentally acceptable Products A and B demonstrated comparable performance to Products C and D with all products providing more than 98% inhibition, Table 1.
| TABLE 1. Results of three electro-chemical tests |
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Partitioned LPR testing. Partitioned LPR tests assess the ability of inhibitors to partition from the oil into the water phase in low-turbulence, low-velocity pipelines such as export pipelines. Test protocols are the same as for brine LPR tests, but a layer of oil is added on top of the test and the inhibitor is dosed into this oil phase. The new environmentally acceptable inhibitors (Products A and B) outperformed Product C. Product A provided corrosion protection very close to that of the traditional inhibitor (Product D). Overall, performance can be ranked as D > A > B > C.
Pre-partitioned RCE testing. The RCE test simulates high-shear flowrates typically found in the field and provides information on the persistency of the corrosion inhibitor film. The tests performed for this study were pre-partitioned tests in which water and oil are shaken vigorously and the water phase is drawn off from the oil phase with the brine used in the RCE test. Again, Product A demonstrated comparable performance to Product D. Product B provided comparable performance to the previous-generation green corrosion inhibitor. In summary, performance in RCE testing was A = D > B = C.
Pre-partitioned weld performance testing. Weld performance tests measure LPR corrosion rates and galvanic current densities between segments of a weld electrode. A key observation in these tests is relative polarity of the galvanic coupling currents, especially the weld galvanic current. If the weld/heat-affected zone (HAZ) segments adopt a cathodic coupling current or if the coupling current is small, risk of weld corrosion is low.
In these tests, a 1% Ni weld material was used to prepare the weld electrode. The tests were again pre-partitioned so oil and water were shaken with corrosion inhibitor prior to running the test with only the water phase. Again, this allows evaluation of the inhibitors’ ability to partition between the oil and water phases. All inhibitors markedly reduced the galvanic component measured across the weld material compared to the blank, Table 2. Products A and B both out-performed Product C with Product A again performing comparably to Product D.
| TABLE 2. Weld performance test results |
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CONCLUSIONS
Clariant Oil Services has developed new, environmentally acceptable corrosion inhibitor products based on a novel amino acid corrosion inhibitor base with a significantly improved environmental profile. In aqueous and pre-partitioned LPR tests, both new-generation “green” products out-performed the old-generation green product. In more extensive and harsher RCE and weld tests, Product A provided comparable performance to the traditional corrosion inhibitor.
The two new products are both classified Gold (no sub) for UK/Netherlands and Yellow for Norway/Denmark. Product A, in particular, provides a clearly viable high-performance, environmentally acceptable alternative to traditional corrosion inhibitors. The new inhibitor bases are manufactured by Clariant and will have full REACH and regulatory support. 
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THE AUTHORS
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Andrew MacDonald has worked for Clariant for more than 13 years in a variety of roles. Upon completing a BSc degree with honors in Aberdeen, he joined TR Oil Services as a chemist working in the hydrates laboratory. Mr. MacDonald later moved into a sales role managing production chemicals for a major UK North Sea oil company. He now manages the Integrity and Hydrocarbons group at Clariant’s Application Development lab in Aberdeen.
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Graham Nelson has worked for Clariant for more than four years. Upon completing a BSc degree with honors in Aberdeen, he joined a regulatory affairs consultancy before joining Clariant Oil Services in 2006. Mr. Nelson currently works as a Senior Chemist group at Clariant’s Application Development laboratory in Aberdeen.
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