COATING MELTING TEMP OPERATIONAL TEMPERATURE RAGE

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1 Temperature Range When a fastener is installed, torquing forces generate heat that can cause its coating to break out or burn away, leaving the bolt vulnerable to corrosion. When we designed Doxsteel Fasteners, we knew that our coating had to be able to take the heat if it was going to resist seizing. Every Doxsteel Fastener can operate in temperatures ranging from -328 F to 1300 F without compromising its coating. ASTM specifications state that coatings working in temperatures higher than one half its melting point are in danger of producing liquid and solid metal embrittlement in the fastener. When compared to other leading coatings with much lower melting points, the difference is clear. In the extreme temperatures that come from torquing, Doxsteel Fasteners keep working. COATING MELTING TEMP OPERATIONAL TEMPERATURE RAGE Cadmium Plating 600 F F Hot Dip Zinc 780 F F Zinc Plating 780 F F Zinc Plating + PTFE 300 F F Ceramic + PTFE 300 F F Zn-Ni Plating 1472 F F 2642 F F info@doxsteel.com doxsteel.com 1544 Sawdust Rd #301 TX 77380

2 Service temperature of DOX studs. This document aims to provide references to the use of the DOX-Steel alloy, under low and high service temperatures, as an anticorrosive plating for studs and nuts under ASTM standards such as A193, A194 and PEMEX standards as NRE-027 and NRF-032. Base material Base materials which mainly dox Steel alloy is deposited cover threaded rods, bolts and nuts generally manufactured under ASTM different denominations of which some examples are given in Table 1, these steels also are detailed in the standard NRF-027 PEMEX-2009 and NRF-032-PEMEX Examples: Service temperatures Material Minimum Maximus C F C F ASTM A193 B7 steel ASTM A194 2H steel Table 1. Service temperatures for steel manufacture under ASTM. However, DOX-Steel plating can be used on any carbon steel substrate. DOX- Steel plating. Dox Steel Coating is a nickel-based alloy with high resistance to corrosion, which by its metallic character (noble metals) is also resistant to low and high temperatures without suffering changes in its structure, in addition to not affect its adhesion to the substrate. The following information details the working temperatures DOX-Steel alloy.

3 - Ni-Co phase diagram (Nickel-Cobalt). T. Nishizawa and K. Ishida, Figure 1 illustrates the nickel and cobalt phase diagram, the DOX-Steel alloy is indicated in blue. Considering the magnetic transition line (magnetic-non magnetic), the alloy use is limited to a temperature of 750 C, which is 300 C above the maximum recommended temperature for a B7 grade steel. Figure 1. Ni-Co phase diagram, a diferentes temperaturas y concentraciones de Ni. - Potential/pH diagram (Pourbaix [E vs ph]). The following diagrams show the thermodynamic stability zones for the DOX-Steel alloy to extreme service temperatures -200 C Figure 2. Potential/pH diagram (Pourbaix) of DOX-Steel alloy at -200 C.

4 25 C Figure 2. Potential/pH diagram (Pourbaix) of DOX-Steel alloy at 25 C. 700 C Figure 2. Potential/pH diagram (Pourbaix) of DOX-Steel alloy at 700 C. Figures 2-4 illustrate the Porbaix diagrams where the stability of the DOX-Steel alloy at the ph (0-14) and potential (-0.5 to -2.0 V) range where Ni, Co and their borides do not present changes in stability. Therefore, the DOX alloy could be used in a wide range of temperature, from low to high without presenting changes in its corrosion resistance. The diagrams were constructed for the indicated temperatures and an aqueous system.

5 DOX-Steel vs other coatings Table 2 presents a brief comparison of service temperatures for the most used coatings in the industry. Coating Melting temperature ( C) Service temperature ( C) Zinc 409 C -25 C to 125 C Cadmium 321 C Above 100 C, highly toxic cadmium oxides are formed. Fluoropolymer 250 C -40 C to 233 C DOX-Steel 1450 C -200 C a 700 C Table 2. Comparison between DOX-Steel plating and other highly used coatings. The fluoropolymer can work at its maximum temperature intermittently. Conclusion. The DOX-Steel plating presents service temperatures ranging from -200 C to 700 C for long periods of time given that the are no phase changes in its microstructure and thermodinamically speaking, the alloy keeps its stability at ph 0-14 and potential from -0.5 to -2.0 V at these temperature values. The DOX-Steel alloy by not presenting changes in its microstructure nor in the conforming elements, it does not present changes in its high anticorrosive properties or in its adherence to the substrate. DOX-Steel plating can be used in an environment with severe temperature changes o under hich temperature ambient conditions. Table 3 presents the chemical composition and service condition of the DOX-Steel plating. Bibliography DOX-Steel plating Chemical composition % Ni % Co % B Service temperature Minimal Maximal C F C F Table 3. Chemical composition and service temperature for DOX-Steel plating. - ASM Metals HandBook Volume 3 - Alloy Phase Diagrams, 1992, USA. - ASTM 2004 Volume Steel--Piping, Tubing, Fittings, 2004, USA. - Normas de NRF-027-PEMEX-2009 y NRF-032-PEMEX-2005 de PEMEX

6 Abstract Field test report for in a E3404 reboiler in Coatzacoalcos, Veracruz It has been demonstrated through field testing of in high temperature-systems installations, that the Ni-Co alloy: Does not present seizing problems between the nuts and the studs at high temperature, F and a corrosive environment level C5. Even with the use of a lubricant which might generate problems at high temperature, such as the generation of molybdenum oxides, the nut turned without interference. There are no changes on the fasteners functionality. There are no changes on the anticorrosion properties of the plating Does not present a risk for liquid metal embrittlement, contrary to other coatings with low melting point such as zinc and cadmium. There are no cutting, grinding, drilling or nut splitting related expenses. There is no downtime related to removing seized bolts, all nuts turn on studs. Test conditions: Test specimen ASTM A193 GRADE B7 ALLOY STEEL STUD, STANDARD THREAD ASME B1.1 CLASS 2A AND 2B, WITH TWO ASTM A 194 GRADE 2H HEX CARBON STEEL NUTS, WITH NICKEL-COBALT ALLOY CORROSION RESISTANCE PLATING ASTM B994 SC18 CLASS 1 SR-0, ER-9. Dimensions 1 1/8-8 X 17 1/4 Operating conditions High temperature C (660 0 F) Corrosion environment level C5 Exposure Location time 2 years Gulf of Mexico The aim of this work was to test and compare the effectiveness of nickel-cobalt alloy anticorrosion plating on fasteners under high temperature and corrosive level conditions, as those presented in a distillation reboiler system. 1

7 1. Background Reboilers are heat exchangers typically used to provide heat to the bottom of industrial distillation columns. Proper operation of the reboiler is vital for effective distillation. Due to all operating conditions this equipment suffer from corrosion at high temperatures. The City of Coatzacoalcos, Veracruz, presents one of the most corrosive atmospheres of the Gulf of Mexico, based on studies carried out by different institutes, and taking as a reference the classification of international standards, the corrosiveness of the atmosphere presents levels of C5, i.e. presents very high corrosion by the presence of aggressive agents, such as CO 2, SO 2, Cl -, S 2-, etc. High temperature corrosion occurs when a metal is subjected to elevated temperatures normally above 100 C, except for very exceptional cases, it is not possible to form a conductive liquid film (electrolyte) on the surface, so a mechanism of electrochemical corrosion cannot take place, instead a chemical reaction takes place between the metal and the aggressive gaseous environment, usually oxygen. The main corrosion products are metal oxides, this oxide is generated directly on the metal surface, with the circulation of electrons and ions happening through the oxide layer. At present there are a number of alloys that have a high resistance to oxidation, up to about 1250 C, these alloys are iron, nickel, cobalt, chromium, sometimes accompanied by silicon and aluminum. The presence of lubricants to benefit torqueing of studs to ensure the adjustment of flanges presents risks at high temperatures, since the components undergo reactions that produce metal oxides, like those of molybdenum. Such oxides, due to their physical characteristics, can generate erosion on the surfaces of the coatings, possible detachment and stop the protection that these infer to the steel. 2. Description of the field test October 2014, The following Stud and Nuts where installed: 1 1/8-8 X 17 1/4 under the following specification: ASTM A193 GRADE B7 ALLOY STEEL STUD, STD THREAD ASME B1.1 CLASS 2A AND 2B, WITH TWO ASTM A 194 GRADE 2H HEX CARBON STEEL NUTS, WITH NICKEL-COBALT ALLOY CORROSION RESISTANCE PLATING ASTM B994 SC18 CLASS 1 SR-0, ER-9. 2

8 The installation was on the E-3404 Reboiler of IDESA Petrochemical Group facility in Coatzacoalcos, Veracruz. Hytork equipment was used for the application of torque according to the information given by the manufacturer. The flange used Doxsteel Fasteners with nickel cobalt and standard studs and nuts with no plating for control and comparison with the following specification: ASTM A193 GRADE B7 ALLOY STEEL STUD, STD THREAD ASME B1.1 CLASS 2A AND 2B, WITH TWO ASTM A 194 GRADE 2H HEX CARBON STEEL NUTS, WITHOUT PLATING. The test parameters are presented below. Test specimens ASTM A193 GRADE B7 ALLOY STEEL STUD, STD THREAD ASME B1.1 CLASS 2A AND 2B, WITH TWO ASTM A 194 GRADE 2H HEX CARBON STEEL NUTS, WITH NICKEL- COBALT ALLOY CORROSION RESISTANCE PLATING ASTM B994 SC18 CLASS 1 SR-0, ER-9. Dimensions 1 1/8-8 X 17 1/4 Operating conditions High Temperature C (660 0 F) Corrosion environment level C5 Exposure time 2 years Facility location Gulf of Mexico Coatzacoalcos, Veracruz Mexico 3

9 1544 Sawdust Road, Figure 1 General view of the test s installation site, IDESA, Coatzacoalcos, Veracruz The conditions to which the studs were exposed correspond both to the site itself and to the installation; the temperature outside the reboiler is 100 C after the insulation layer, which indicates that the temperature at which the stud was subjected was about 350 C (660 F). The installation time was 2 years. Molybdenum base lubricant was used in the installation to observe the effect of oxides produced by high temperature on the Ni-Co alloy. 4

10 3. Follow-up after 2 years in service In January 2017, a follow up visit to the IDESA Coatzacoalcos Group facility for the inspection and removal of the Doxsteel Fastener studs, with the following findings: After two years of service at high temperature, the Doxsteel Fasteners (pointed with the arrows in the images) do not present corrosion by effect of the high temperature. The studs maintain the brightness, there is no oxidation reaction on the surface that affects the appearance. The removal of the studs was performed with Hytork equipment using the same pressure in the pump with which they were installed. The remaining studs with no coating that where installed at the same time, show a brown color throughout the surface, which is indicative of corrosion products of the steel due to high temperature. Figure 2 Location of Doxsteel Fasteners studs in the high temperature equipment 5

11 Figure 3 Stud from Doxsteel Fasteners without corrosion damages Under conditions of high temperature the formation of dry oxides and/or carburized particles begin to produce a galling process, i.e. seizing of parts between the surface of the nut and the face of the flange. During the dismantle, the uncoated studs required twice the pressure in the hytork equipment for the nut to turn. This is indicative that the corrosion products are preventing the nut to turn and eventually will seize the nut and the bolt. As part of the observations given by the operators, it was found that the disassembly time for the nickel cobalt alloy plating stud was reduced up to 60%, they all turned with ease. In this test there were no seized bolts. The operators are very familiar with nut splitting, drilling, cutting and some times metal disintegration of studs. Their experience is that seizing occurs after the third year, in about 10 to 20% of the bolts, this number increases to 40 to 50% after the fourth year. 6

12 4. Evaluation of the Doxsteel Fasteners after removal The stud was evaluated to detect in detail the possible faults by a visual analysis using focal amplification of the areas with apparent damage. There was no damage found in any of the threads, nor loss of the plating. Figure 6 shows the wrenching flat of the nut with damage caused during installation by a torque tool; however, the plating remains without change and there is no indication of penetration of corrosion products. The stability of the plating is indicative that it has not undergone any type of alteration. Many platings with low melting points, such as Zn, present a high risk of embrittlement due to liquid metal, HDG (Hot Deep Galvanized) platings are very susceptible to this, this kind of embrittlement induces loss of ductility in the steel, generating a risk of fracture by the stress to which they are subjected. The removed stud (Figure 6) show some small stains from the lubricants used during installation, the plating did not suffer any changes, only a color change can be observed, neither oxides nor possible erosion to the surface of the plating was presented. Figure 4 The studs from Doxsteel Fasteners without corrosion damages 7

13 Figure 5 Stud after removal, all the stud and both nuts are shown, no section of the fastener shows peeling or loss of the coating. Figure 6 Stud and nut after removal, the interior thread of the nut shows no damage, the stains are residues of materials used during the installation. 8

14 Figure 7 Inferred damage to the surface of the nut by the installation tool; however, no advance of corrosion products is observed. 5. Conclusions and recomendations The Doxsteel Fasteners that were installed in the Reboiler E-3404 in January 2015 and removed from the field test on January 2017, do not present corrosion damage at the time of the removal as shown in the images above. The ease of dismantle and visual examination of the interior threads of the nut, show that there is no formation of corrosion that will eventually seize the nut and the bolt. The test was indicative for 2 years, but we can conclude that the fasteners will not seize in this same condition in several years. Doxsteel Fasteners has a written warranty that the fasteners will no seize in 5 years in any condition. Due to the high temperature conditions under which these reboilers operate and their importance in the industry, it is necessary to provide preventive and corrective maintenance in a way that the least possible production time is lost; therefore, materials that facilitate periodical replacement are of great importance due to the cost that this operation represents. As a result of this field test, it is recommended to use nickel cobalt alloy plating on studs and nuts to eliminate seizing in high temperature applications. 9

15 6. References Electrochemistry and corrosion science, Nestor Perez Kluwer Academic Publishers Handbook of Corrosion Engineering. Pierre R Roberge. MCGraw-Hill, 2000 La corrosión atmosférica y su impacto en la economía veracruzana, José Luis Ramírez Reyes, Domitilo Pereyra Díaz, Norma García Navarro, Leticia Valencia Argüelles y Victorino Juárez Rivera. Effect of Zinc Galvanization on the Microstructure and Fracture Behavior of Low and Medium Carbon Structural Steels, Engineering, 2013, 5, , Ignatius C. Okafor, Ronald J. O Malley, Kaushal R. Prayakarao, Heshmat A. Aglan. Corrosion of metals and alloys Corrosivity of atmospheres Classification, determination and estimation, INTERNATIONAL STANDARD, ISO Author Oscar García Delgado Corrosion and Materials Manager Approved by Jose Hernandez Espinoza VP 10