A New Formulation Addressing Base Resin Challenges and Carcinogenic Concerns for Water Pipeline Cathodic Protection

Traditional epoxy coatings used for water pipeline cathodic protection have several shortcomings, including limited availability, high cost, and carcinogenic concerns. To address these challenges, a new, food-grade epoxy coating that is affordable, meets all technical requirements, and is free of carcinogenic substances was developed.The study involved testing various kinds of reinforcing fillers, non-reinforcing pigments, red pigment, and BYK additives to formulate the epoxy-based coating. Curing experiments were then conducted by formulating the coating with a fixed ratio of curing agent and spraying the resins onto mild steel panels for testing.The results demonstrated that the new formulation has good compressive strength, adequate impact resistance, and Shore D hardness in the range of 60-70, which is expected for this type of application. The abrasion resistance of the coatings increased with increasing hardness.Overall, the new food-grade epoxy coating is a promising alternative to traditional epoxy coatings for water pipeline cathodic protection. It is affordable, meets all technical requirements, and is free of carcinogenic substances.Key words: Epoxy Resin, Coating, Food Grade, TETA


Introduction
Coatings are used on buried pipelines to protect them from corrosion [1].Cathodic protection is also used for this purpose, but it is considered the second line of defence in the gas/oil storage, transmission, and distribution sectors [2].Therefore, today's coatings must provide better protection than their predecessors, be able to function under severe operating conditions, and be easy to apply even when conditions are less than ideal.Additionally, they must be a cost-effective solution for maintaining pipeline integrity.The important parameters for corrosion protection are the adhesion of the coating to the pipeline surface and the resistance of the coating to the permeation of water, oxygen, and/or ions [3].The major factors that affect the performance of protective coatings, according to NACE Standard RP0169-96 Section 5, are: a) surface preparation, b) wetting, c) bonding, and d) adhesion-cohesion phenomena [4].Pipeline coatings are typically applied in three ways: • Fusion bonded epoxy powder coating • Application of multilayer coatings, such as three-layer polyethylene/propylene • Thermoplastic polymer coating [5] Epoxy coating is a preventative treatment that improves the quality of water in pipes and can serve as a frontline defence against corrosion, erosion, leaks, mold growth, and premature failure of metal pipes [6].The rate of corrosion is inversely proportional to the resistivity of the electrolyte and directly proportional to the electron flux.Applying a high-resistive polymeric solution (such as epoxy, vinyl, or chlorinated rubber) and increasing its thickness on a still surface can improve resistance and, consequently, corrosion protection.Similarly, using inhibitive pigments in coatings, such as zinc chromate, red lead, and zinc phosphate, can further improve corrosion resistance of pipeline surfaces [7].The spray-on-lining procedure for epoxy-resin coatings typically involves steps as drying the pipes, cleaning the pipes with pressure and sandblasting, applying the epoxy mass with pressure, and drying the coating.The pipes are ready to be flushed and used within 12-24 hours after the coating procedure is complete.This process is less expensive and non-invasive than traditional pipe replacement, which is why it became popular in Europe and the USA in the 1980s and 1990s [8][9][10][11][12][13].However, there were several challenges associated with the spray-on-lining process, including:

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Proper cleaning of the inner surface of the pipe • Finding a formula with a suitable curing time

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Efficiently spreading the lining materials All these factors are essential for ensuring that the resin adheres properly to the pipe and does not leach into the oil or water.Epoxy coatings used in pipeline applications are typically two-part liquid epoxy systems, consisting of an epoxy resin component and a hardener component.Due to the presence of several toxic leaching ingredients, such as bisphenol A (BPA), diglyceryl ether (BADGE), and other organic compounds, epoxy-based coatings are not allowed in Germany and are not recommended in Sweden [14][15][16].Additionally, epoxy coatings are subject to strict countryspecific regulations and procedures.Recently, the price of food-grade epoxy resin has increased dramatically due to limited availability and rising base epoxy resin prices.This has caused the profit margin for food-grade epoxy coatings to decrease.Other manufacturers offer less expensive epoxy coatings, but these are not food-grade and contain Triethylenetetramine (TETA), which is a carcinogen [17][18][19][20].In response to these challenges, in this paper, development of a fully food-grade epoxy resin is discussed that does not contain TETA or any related materials.

Materials
Liquid epoxy base resin with an epoxy equivalent weight of 185-194 g/eq (grams per equivalent) and a viscosity of 11,000-14,000 cps at 25°C was sourced from Aditya Birla Chemicals.Diluents (reactive/non-reactive), cashew nutshell liquid, and reaction products with 1-chloro-2,3epoxypropane were procured from Ark Golden India Pvt Ltd.The hardener used was an amine-based hardener, specifically a Mannich adduct of cardanol, formaldehyde, and amine from Ark Golden India Pvt Ltd.Namlon T 206, a thixotropic agent, was purchased from Unique Enterprises, Mumbai.Fumed silica (anti-sag agent and anti-settling agent) was obtained from Evonik, Germany.The preparation of coating: • Various kinds of reinforcing and non-reinforcing fillers were purchased from local sources.

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Red pigment, namely inorganic red pigment, was supplied by Cathay Industries Asia Pacific Limited, Hong Kong.

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The curing experiments of the prepared resins were formulated as liquid epoxy coatings with a fixed ratio of curing agent (3:1 volume of Resin: Hardener).

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The resin part was heated to 60-70°C before mixing for ease of application without sagging.

Testing of the coatings
These resins were sprayed (by using an air spray gun) with wet film thickness, WFT, 400 µ.It is common to use mild steel panels (15 cm×l0 cm) to evaluate the different properties of coatings.The other side of panels were coated against corrosion environments by using coal tar epoxy primer.The tested side was blasted and afterward cleaned to apply the coating materials.Then the panels were subjected to different testing procedures to assess the mechanical properties as well as durability.

Results and Discussion
The Viscosity and Sag test is done for all the samples in the similar conditions mentioned below.The viscosity value of tested samples having different compositions is provided in Table 1 as well as in Figure 1.To compare the viscosity of standard sample with a prepared sample at different temperature, the composition F3 was chosen, and they are comparative results are summarized in   Engineering Chemistry Vol. 6 13 For the testing of Sag properties, the epoxy was heated up to 60 o C temperature and hardener was heated up to 40 o C and then mixed thoroughly and then with the help of an 800-micron applicator the mixed epoxy was applied on a 40 o C heated metal panel to observe the sag.The sag test carried out at different location had given promising results and as per the norms, it passed the test [15].

Mechanical Testing:
In past two years, various coating systems (different formulations) have been tested to investigate their potential use as an internal pipeline coating.In this paper, we will deliberately introduce three coating systems that were subjected to mechanical tests.Results of the mechanical testing are presented in Table 3 which is given below.All three coatings (A, B, and C) showed pull-off adhesion strength in the 80-900 psi range, which is typical for good coating systems.All coatings failed primarily adhesively, indicating that the pull-off strength obtained is near the maximum value for the coating.All coatings showed good abrasion resistance, but coating C had the lowest compressive strength at 130 psi.
In various applications, cured epoxy is subjected to axial loads or forces.In these applications, an epoxy with a high compressive strength is the best choice to resist these forces continuously without being crushed.All the coatings in this study have good compressive strength.The coatings showed slightly lower hardness (Shore D) values than the standard coating (all in the range of 60-70).This is expected for these types of coatings.However, a coating used for an internal pipeline should have adequate impact resistance to withstand accidental or unavoidable impact during placement and compaction.All the coatings in this study have adequate impact resistance.
Hardness is proportional to the abrasion resistance properties of a coating.As expected, the abrasion resistance of the coatings increased with increasing hardness.Hardness also indirectly proves the degree of cure of a coating, and it is important for comparative purposes or determining the degree of cure.The prepared coating showed comparatively less hardness and impact resistance properties in comparison to the standard coating system, but this does not have a significant impact on the coating's performance in its intended application.Dielectric strength depends on the thickness of the specimen and the test temperature [16].It provides an idea about the insulating strength of the materials.According to Sauni Yojna, the dielectric strength should be at least 250 V/mil.All the coatings in this study had dielectric strength values of at least 400 V/mil (Table 4).Electrical continuity is defined as the ability to conduct electric current.This test was performed on all the coatings, and no holidays (film discontinuities) were observed (Table 4).This test method provides an idea of whether the protective system can be used for a specific application without showing any film discontinuities that are not readily visible to the naked eye.No Holiday observed Chemical immersion studies were conducted according to the ASTM D 543 standard on formulations cured for 7 days at 25°C.One inch by three-inch (1" x 3") samples of 1/8" thick castings were prepared and fully immersed in reagents, specifically H2SO4, NaOH, and deionized water.Two samples of the standard formulation and one of the prepared solutions were immersed in each reagent, and the physical appearance of each immersion was observed after 28 days.By simply comparing the 28-day immersion test results, all the prepared solutions did not change much except for a shade variation/colour change, as shown in Figure 2, Figure 3 and Figure 4, in terms of physical appearance compared to the standard solution used for pipeline coating.
Similarly, cathodic disbonding studies were also conducted.Various parameters play a significant role in cathodic disbonding, such as electrolyte composition, the presence of hypochlorite in the electrolyte, dry film thickness, oxygen concentration in the electrolyte, and applied potential [17].Samples for cathodic disbonding studies were given a circular holiday in the middle (6 mm in diameter) and polarization was done with a potentiostat.Table 5 shows that the new formulation did not have any serious impact.When the hardener is added, the resin will become more viscous and eventually lose its ability to flow, which is called the gel point of the resin system [16].The gel time of both the standard and prepared resin formulations at room temperature and at a higher temperature of 40°C were measured.The gel time of the standard resin at room temperature was observed to be around 27 minutes, while all the new formulations had gel times in the range of 25-27 minutes.Similarly, at a higher temperature (e.g., 40°C), the gel time of the newly prepared solutions was slightly lower than that of the standard solution (e.g., 7 minutes for the standard solution and 6.2 minutes for recipe B).  [19][20].However, the resin may crystallize, or the hardener may darken, but this does not affect the performance of the epoxy resin.This is especially useful for warehouses where the materials are stored for prolonged periods of time.In this study, shelf life as measured is shown in Table 6.Samples were kept for 2 years and used it for coating.It was found that the gel time has increased with issues with surface adherence.

Conclusions
In conclusion, the new food-grade epoxy coating has good compressive strength (≥ 30 MPa), adequate impact resistance (≥ 10 J/m), and Shore D hardness in the range of 60-70.While the new formulation has slightly lower hardness and impact resistance than the standard coating system, this does not significantly impact its performance in its intended application.Overall, the new food-grade epoxy coating is a promising alternative to traditional epoxy coatings for water pipeline cathodic protection, with comparable technical properties and without the associated health concerns.

Fig. 1 .
Fig. 1.Viscosity against temperature of different composition used for preparation of Epoxy coting system

Sample 5 :
LHS Panel: Unexposed, RHS Panel-Exposed Sample 6: LHS Panel: Unexposed, RHS Panel-Exposed 16 Engineering Chemistry Vol. 6 All variants were cast on 150 mm X 150 mm tin plates, using a 200-1000 µm sag index applicator.The viscosity of the variants was measured by a Brookfield Viscometer (using mostly Spindle 04 at 60 rpm) at 25 °C.

Table 2 .
The viscosity test was done at approx.67 o C, 63 o C and near 60 o C temperature i.e., the application the temperature of the FGE material and the sag test was done with the mixture of 1:0.2 weight ratio of epoxy and hardener (ark 185) respectively.

Table 1 .
Viscosity and mixing ratio of different composition used for preparation of Epoxy coating formulation

Table 2 .
Effect of temperature on viscosity of standard and single composition

Table 2
provides the comparison of the viscosity test done at both the labs.As per the data given above, viscosity test results were quite similar in both the labs and within the application range at elevated temperatures of over 60 o C.

Table 3 .
Mechanical Testing of Various Formulations for Internal Pipeline Coatings a a All properties were measured a per the applicable test standard methods; therefore, reported values are average of multiple trails.

Table 4 .
Electrical Testing of Various Formulations Used for Internal Pipeline Coatings a

Table 5 .
Gel time value for Sample A and Sample B Epoxy resin without solvent does not change its shelf life much if it is stored in a sealed container in the appropriate environmental conditions

Table 6 .
Shelf life of new formulation