White Paper Effective February 2016

Laser cladding protection of hydraulic cylinders Author name: Umar Farooq Eaton

Introduction

When hydraulic cylinders are exposed to harsh operating environments, corrosion protection plays a crucial role in the reliability and durability of the equipment. Without proper protection, hydraulic equipment can suffer pitting, crevice development, and other forms of corrosion, leading to inefficient operations, equipment failures, unwanted down times, and sometimes catastrophic consequences. Eatonite® Anti-Corrosion Laser Cladding, a high-performance, field-repairable coating, has proven highly effective in protecting hydraulic cylinders in demanding applications and environments.

Why protection is crucial

Hydraulic cylinders are often called upon to do heavy lifting in harsh environments. In off-shore oil rigs, saltwater environments often subject equipment to corrosive conditions [1, 2].

Other marine applications, such as drilling and dredging, also face corrosive conditions. Land-based hydraulic cylinder applications, such as construction, manufacturing, and power plant equipment, may operate in less corrosive conditions, but encounter dust, dirt, and other elements, necessitating coating protection of cylinder rods and other equipment. Laser cladding provides protection for a variety of applications, including:• Energy (oil, power stations, windmills)• Marine (cranes, drilling, dredging)• Industry (process machinery, milling, mining)

Depending on the application, hydraulic equipment can encounter various environmental factors, as summarized in Table 1.

Table 1: Environmental factors per EN-ISO 12944-2 [3]

EnvironmentIndustrial atmosphere

Potable and fresh water

Brackish and saltwater Marine atmosphere

SoilSplash zone Submerged Open Sheltered

Corrosivity Very low - very high Low – medium Very high High Very high High - very high Low

Category C1, C2, C3, C4, C5-I Im1 C5-M / Im2 Im2 C5-M C5-M Im3 Environmental characteristic

Industrial condition (e.g. SO2, salinity)

Rain water and treated water

Seawater (estuaries and coastal areas)

Seawater in the open oceans

Seawater salts and varying humidity levels

Local seawater salts and varying humidity levels

Salinity 1 - 300 ppm 1.5-3.5% 2.5 - 3.5% 2.5 - 7% 2.5 - 15% 2.5-3.5%

pH 6-9 7.5 - 8.5 7.5 - 8.5 6-9 3-9 7-9

Temperature(degrees C) 1-3 -2 to 30 -2 to 30 -20 to 50 -20 to 50 -2 to 30

Humidity, RH ----------- 100% ---------- 30 -100 % 10 -100 % -------

Pollution Low Low Low Low to high Low to high Low to medium

* Categories defined as follows:C1: Very low Im1: Immersion in fresh water

C2: Low Im2: Immersion in sea or brackish water

C3: Medium Im3: Buried in soil

C4: High C5-I: Very high (industrial) C5-M: Very high (marine)

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White paper February 2016

Laser cladding protection of hydraulic cylinders

Hydraulic equipment can also incur damage from material handling. Impacts from swinging chains and cables, falling debris, or dropped equipment can produce unwanted nicks, dents, and cracks, leading to corrosion and leakage. By coating cylinder rods and other equipment with Eatonite laser cladding, damage from material handling can be minimized, and even repaired in the field .

Laser cladding can have both short-term and long-term economic benefits. As a field-repairable technique, laser cladding can reduce repair cost and down time. The increased durability of properly coated equipment can improve reliability, reducing operating expenses and total cost of equipment ownership over the life of the equipment. For example, a day rate in oil production (the amount a drilling contractor gets paid for a day of operating a drilling rig) can range from $200,000 to $600,000 for a floating rig[4]. For each day of down time, costs can quickly skyrocket, emphasizing the importance of equipment reliability.

How it works

Laser cladding[5] produces a metallic coating with a strong metallurgical bond between the coating layer and a substrate material such as carbon steel in case of cylinder rods. Using precise, state-of-the-art lasers such as the high power diode laser (HPDL) as a controllable heat source, metallic powder is injected into the system by nozzles. Energy from the laser beam produces a shallow, molten cladding pool. Filler material powder is injected into the beam and the pool. As the laser beam passes through the area, the cladding pool solidifies rapidly, leaving the desired build-up of cladding material with minimal dilution of the base material. Care must be taken to keep the heat-affected zone (HAZ) soft enough to avoid brittleness and potential delamination with the substrate.

The result is a protective coating with high ductility, resistance to bending, high strength, and numerous other characteristics, as shown in Figure 1. When compared with other types of coatings, Eatonite laser cladding offers the following: • Optimized corrosion, wear, scratch, and impact resistance• Consistent coating depth• Strong adhesion due to the metallurgical bond• Hardness throughout depth and length without cracking• Optimized ductility and toughness• Optimized surface characteristics designed for longer seal life• Certified production welds tested both destructively and

non-destructively before and after the weld to verify superior quality

Resisting cracks, wear, and other failures

Prevention of cracks, wear, and fatigue in hydraulic equipment is critical in many fields. With a typical hydraulic cylinder, a piston connected to a piston rod moves back and forth in a cylindrical barrel. A hydraulic pump brings in a fixed or regulated flow of hydraulic fluid, typically oil, to the hydraulic cylinder, to move the piston. Wear and corrosion resistance are particularly crucial on the outer diameter of the piston rod.

Different operating conditions present different challenges to hydraulic cylinder equipment. Corrosion, impact from debris, bending, high temperatures, and various combinations of these conditions may be encountered.

With a surface hardness approaching 450 HV (Vickers Hardness Number), Eatonite laser cladding is highly resistant to wear and scratches. A comparison of Eatonite laser cladding hardness with other coating technologies is shown in Figure 2. The microhardness chart shows how Eatonite laser cladding is hard at the outer surface but follows a smooth transition curve to become soft at the HAZ. Other coatings may be either soft at the surface, indicating low wear resistance, or reach a plateau just below the surface, indicating possible issues with disbonding/delamination.

Laser cladding microhardness summary

0.000200

250

300

350

400

450

500

550

0.010 0.020 0.030 0.040 0.050

Competitor I

Competitor U

Competitor C

Eatonite

Competitor S

20 HRC

Depth (inches)

Mic

roh

ard

nes

s (H

V)

30 HRC

40 HRC

35 HRC

50 HRC

45 HRC

Figure 1: Eatonite cladding exhibits excellent quality! No cracks or pores, smooth substrate adhesion, uniform coating thickness, zero dilution.

Micro-hardness indentations not cracks

1350 µm

Eatonite cladded on S355J2 carbon steel base material 100X

0.01 Inch

Figure 2: Comparison of Eatonite laser cladding with other coating technologies.

Eatonite laser cladding also provides high impact resistance — up to 24 foot-pounds of energy without cracking. Spray-type coatings, such as high-velocity oxygen fuel (HVOF) coatings typically top out at only 8 foot-pounds of impact energy without cracking. In non-technical terms, when struck with a ballpeen hammer, Eatonite laser cladding may dent, but will not crack. With a bond strength exceeding the strength of the steel base metal (>50,000 psi), Eatonite laser cladding will also not spall or chip. In comparison, if an HVOF thermal spray coating is struck with the same ballpeen hammer, the HVOF or hard chrome plating or plasma sprayed ceramics will crack and spall.

Eatonite laser cladding’s ductility provides high flexibility without cracking. The product can be applied to cylinder rods up to 21 meters long without cracking and can withstand up to 180-degree bends, as shown in Figure 3.

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White paper February 2016

Laser cladding protection of hydraulic cylinders

Figure 3: Eatonite laser cladding’s ductility provides flexibility without cracking.

Combining strength, high ductility, and minimal porosity, Eatonite laser cladding can help avoid fatigue cracks and limit the propagation of other flaws like solidification or shrink cracks, as shown in Figure 4.

Cylinder rod

Rod coatingDiscontinuitiesin coating Impact damage Cracks Water ingress into the discontinuities

Water reaches the bondlineinitiating corrosion

Corrosion causes the bondto fail, the coating falls off

Figure 4: Cross sectional view of the rod coating indicating large cracks (red arrows), porosity (blue arrows) and corrosion in scalloped bond line (black circle)

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Laser cladding protection of hydraulic cylinders

Field repairable

A key distinguishing trait of Eatonite laser cladding is its field repairability. Using common welding processes, Eatonite laser cladding can be repaired on site, saving significant time and money. Depending on whether the damage is impact or linear, as shown in Figure 5, different tools and techniques can be used. In general, an in-line die grinder with carbide burs, a right angle die grinder, a cleaning solvent to remove oil and grease, and appropriate welding tools are the key tools. Proper training is required prior to conducting any field repairs of laser cladding.

Figure 5: Deep linear discontinuities like cracks and gouges require weld repair as shown above in a linear impact.

Seal compatibility of coating

The tribological interaction between rod surface, seals, and various fluids used in hydraulic systems can present challenges. System requirements such as pressure, temperature, velocity, friction, lubricity, fluid media, and frequency of operation all play vital roles in determining the seal choices. One seal system may work well in a certain application, but not in another. For that reason, proper seal selection with rod coating surface finish parameters is key to ensuring long-term satisfactory performance [6].

As technologies such as laser cladding have advanced, expectations for surface finish and seal life have risen. Various seal manufacturers establish product-specific surface finish requirements, but most specify additional parameters such as Rp (peak height), Tp (material bearing ratio), and Rz (average of largest peak to valley sums).

To design the optimized parameters for Eatonite laser cladding surface finish, a detailed testing program was established. The program has run millions of cycles of testing (each run is 2 million cycles) with various fluids to establish optimized parameters for various applications. Surface finish requirements include the key surface finish parameters tailored to the application needs. Due to these extensive research efforts, no cylinders using Eatonite laser-cladded rods have ever been returned to the factory due to leakages.

Certifications

Eatonite laser cladding has been certified by international organizations such as the Norwegian Det Norske Veritas (DNV) [7], as shown in Figure 6.

Eatonite L1 Laser Cladding became the first DNV-certified laser clad coating certified by passing all testing requirements outlined by the Joint Industry Project (JIP) in the “Guideline for Qualification of Wear and Corrosion Protection Surface Materials for Piston Rods.” Established by international oil and gas manufacturers, operators, contractors, and suppliers, this standard established recommended practices for documenting requirements for major subsea components.

Figure 6: Eatonite laser cladding was the first DNV-certified laser clad coating.

The specific tests performed included:

• Saline Droplet Test (DNV-C1)• Electrochemical Porosity Test (DNV-C2)• Resistance to Rapid Deformation (DNV-M1)• Hardness testing (DNV-M2) - Hardness & HAZ• Dynamic Bend test (DNV-M3)• Metallographic examination (composition, cracks, thickness,

microstructure, porosity, content and slag-oxide content)• Surface roughness, surface finish and optical imaging dye

penetrant• Wear Abrasion Testing • Anodic polarization, critical pitting temperature and critical crevice

temperature tests

The successful results can be attributed to tight process control, along with high powder quality and laser cladding.

Comparison of coating technologies

A summary of laser cladding properties compared with other coating technologies is shown in Table 2. Plasma sprays and HVOF type coatings are generally harder but exhibit high porosity, low bond strength, low impact resistance, and brittleness. To minimize porosity in these coatings, an additional operation such as chemical sealant is often applied, but this can lead to inconsistent pore sealing and evaporation of sealants at high temperatures. When Eatonite laser cladding was certified by DNV, the DNV rods exhibited less than 0.02 percent porosity. In contrast, the best HVOF has porosity ranging from 0.3 to 1 percent, with most HVOF coatings containing 2 to 5 percent porosity. Also, chrome plating is often cracked as manufactured. The low bond strength and low impact resistance can lead to delamination and spall offs. Plasma Transferred Arc (PTA) is a process similar to laser cladding but with moderately high porosity content and higher dilution. Dilution is defined as the amount of mixing of the clad and the base/substrate materials. A low dilution value is preferred to obtain a surface that is similar to that of clad

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White paper February 2016

Laser cladding protection of hydraulic cylinders

material, and the clad material properties are fully preserved [8].

Laser cladding is categorized as a “low hydrogen” welding process. The cladding pool (melt zone) is protected by a shielding of the inert gas Argon. The powder flow lines feeding the laser cladding torch also deliver Argon. In some applications, the coaxial flow of Argon is augmented with an additional trailing gas shield. In this manner there is no pumping of elemental Hydrogen into the heat affected zone of the steel base metal. With Eatonite laser cladding, post-

cladding baking of the finished hydraulic cylinder rod is not needed. As such, hydrogen embrittlement common with chrome plating is a non-issue with Eatonite laser cladding.

Eatonite laser cladding provides outstanding resistance to stress corrosion cracking (SCC). In this regard, laser clad Eatonite laser cladding resists SCC better than other products such as cobalt-based or nickel-based coatings

Table 2: Comparison of laser cladding with other coating technologies

Compare coating Plasma spraying HVOF PTA Laser cladding

Heat sourceNontransferred electric arc Combustion flame Transferred

electric arc Focused laser beam

Coating thickness0.05 to 0.50 mm (0.002 to 0.020 inch)

0.12 to 0.70 mm (0.005 to 0.028 inch)

0.64 to 1.90 mm (0.025 to 0.075 inch)

0.40 to 1.90 mm (0.015 to 0.075 inch)

Bond type Mechanical Mechanical Fusion weld Fusion weld

Bond strength2,500 PS typical (17.2 Mpa)

< 13,000 psi (89.6 MPa)

> 50,000 psi (> 344.7 Mpa)

> 50,000 psi (> 344.7 Mpa)

Behavior Brittle, easily cracked Brittle, easily cracked Ductile, no cracks Ductile, no cracksPorosity content 3% to 10% 0.5% to 5 % 0.5% to 2 % 0.05% to 0.5 %Dilution None None 3% to 12% 0.5% to 2%Topcoat materials Ceramics

• Chromia-Titania• Alumina-Titania• Zirconia

CoCrWCNiCrBSiNiCr-CrC

Inconel 625UltimetStellite (all)

Inconel 625EatoniteUltimetStellite (all)

Bond coat materials

Metals• NiCr80/20• NiAl• MCrAlY

None None None

Laser cladding is essentially free of constituents deemed harmful to the environment. Conventional rod coatings such as hard chrome plating (HCP) often include toxic chemicals such as hexavalent chromium. Regulations such as the European Union Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) include measures to eventually phase HCP out.

Conclusion

Laser cladding provides a high-performance, environmentally friendly coating solution in protecting hydraulic cylinders. Eatonite laser cladding provides a fully proven, field-repairable, coating with all the necessary ingredients to replace the traditional coatings and successfully meet customer needs in the harshest of operating environments.

References

1. “Premature Failure of Riser Tensioner Piston Rods Exposed to Offshore Splash Zone Operation – Status and Review of Critical Multi-degradation Factors,” by C. Ohe, R. Johnsen, and N. Espallargas, paper 09199 in 2009 NACE Corrosion Conference and Expo.

2. “The piston rod — simple, yet critical,” http://hydraulicspneumatics.com, October 13, 2010.

3. “Guideline for Qualification of Wear and Corrosion Protection Surface Materials for Piston Rods” DNV Report No. 2009-3295.

4. http://www.rigzone.com/data/dayrates/, November 20, 2015. 5. Laser Cladding by Ehsan Toyserkani, Amir Khajepour, Stephen F.

Corbin, CRC Press, New York, 2005.6. “How piston-rod coatings affect hydraulic seals,”

http://machinedesign.com. 7. https://www.dnvgl.com/8. “FEM modeling and experimental verification for dilution control

in laser cladding,” by J.T. Hofman, D.F. de Lange, B. Pathiraj, and J. Meijer in Journal of Materials Processing Technology, pp 187- 196, Vol 211, Issue 2, Feb 2011.

About Eaton

Eaton is a power management company with 2014 sales of $22.6 billion. Eaton provides energy-efficient solutions that help customers effectively manage electrical, hydraulic, and mechanical power more efficiently, safely, and sustainably. Eaton has approximately 102,000 employees and sells products to customers in more than 175 countries. For more information on Eatonite Anti-Corrosion Laser Cladding, visit www.eaton.com/Eatonite.

About the author

Umar Farooq is global engineering manager for cylinder business at Eaton Hydraulics. He holds a Ph.D. degree in mechanical engineering and has experience in control and vibration systems. In his present role, he has been involved in developing and implementing surface technologies to hydraulic systems, particularly on cylinder rod surface coating technologies.

Acknowledgements

The author wishes to thank Mike Killian, principal engineer in Eaton’s corporate research and technology group, for his guidance on various aspects of coating technologies. Any opinions, findings, conclusions, or recommendations expressed in this material are those of the author and may not necessarily reflect the position of Eaton.

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© 2016 EatonAll Rights ReservedPrinted in USAFebruary 2016

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