Spray balls are used in the pharmaceutical and food industries to facilitate the regular cleaning of tank and piping. They allow the tanks to be cleaned by dousing the interior surfaces with high-velocity jets of hot water and/or chemicals. This process is called Clean-In-Place or CIP.
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Spray balls come in many shapes and sizes and have various functions. One type, a fixed-spherical spray ball design, is pictured in Figure 1. This particular spray ball is a permanent static mount, designed to direct multiple high-velocity jets against the tank wall. Some spray balls are thick-walled to allow each drilled hole to become a very efficient cleaning jet. Another design is thin-walled to allow each hole to act as a divergent spray. There are mushroom-shaped balls that provide room for more holes to be directed upward to clean overhead surfaces like those illustrated in Figure 2. Spray balls may be fixed or detachable. Some are dynamic so they rotate; others just spray the cleaning solutions where they are designed to spray. The hole pattern and diameter are usually specific for the system being cleaned. The hole pattern allows 360-degree coverage, 180-degree upward spray, 180-degree downward spray or 270-degree spray. Type 316L stainless steel is the most common material of construction. Most have an electropolished surface that is smoother than 20 Ra (0.5 μ).
What is Clean-In-Place or, as more commonly called, CIP? It is the use of special disinfectants, hot water and/or steam to kill bacterial organisms that may affect the product. Use of steam usually is referred to as Sterilize or Sanitization-In-Place or SIP. Both are highly efficient processes that can be automated and designed to provide maximum coverage. Spray balls make this possible. There are five factors to be considered in the cleaning process: temperature, time, required chemicals, pressure, and the coverage by the spray balls. Once the cleaning cycle parameters are defined the entire process can be automated.
The process must be designed to clean thoroughly and in a timeframe that allows optimum production. Therefore, the cleaning cycle is usually designed to be more efficient than is perhaps necessary with greater volumes of solution at higher velocities.
Pharmaceutical plants use huge quantities of pure water. Two basic grades of water are used: Purified Water and Water for Injection. Purified Water is used for non-injectable applications and products that do not contact blood. It must be biologically and chemically pure so neither undesirable chemicals nor harmful bacteria are introduced into or onto the body. Water for Injection, or WFI, is the next step up in product purity. It must meet the same chemical requirements as Purified Water, but in addition must meet the highest requirements for being free from bacterial contamination. WFI is used wherever the water directly enters the bloodstream. This water quality must meet the requirements of the United States Pharmacopeial Convention (USP), which defines the purity levels that the industry must meet. Superimposed on this is FDA guidelines and requirements.
Figure 3. High-contrast view of a tank dome showing the spray ball and the impingement erosion on the interior of a polished stainless steel tank. The eroded areas are a source of Class 1 rouge in the entire water system.This standard results in water with a specific conductivity of less than 1.25 μS/cm, making water almost completely devoid of any ions whatsoever. Since water is nearly a universal solvent it is extremely reactive. This sets the stage for rouging to occur. Figure 2 shows the interior of a tank with mushroom head spray balls. Rouge streaks are visible along the walls and on the spray ball stems. The streaks appear to originate from the tank head.
Rouge is iron oxide. It is usually red, but it can be yellow, reddish-brown, brown, blue or black. The color depends on the valence of the iron and the water of hydration in the oxide. (For a more detailed explanation see "Rouging of Stainless Steel: Why Good Stainless Steel Turns Red," Flow Control, March , Page 181,2. An in-depth analysis is available in "Rouging of Stainless Steel in High Purity Water," ASM Handbook, Volume 13C, Page 15, .)
Rouge may be categorized in three classes:
It is important to remember that Type 316L stainless steel is 70 percent iron. (For a better understanding of stainless steel and how it corrodes see the "Stainless Steel Primer" series that appeared in Flow Control, August, September, October 4, 5, 6.) Any condition that destroys the passive layer on the stainless steel will result in oxidation of the iron according to the following equation:
2Fe0 + 4H2O → 2FeO(OH) + 3H2
2FeO(OH) → Fe2O3 + H2O
The Fe2O3 is the common red rust that is known as hematite. The passive layer is what gives stainless steel its corrosion resistance. It can be destroyed chemically or mechanically. Acid chlorides or other aggressive acids usually are responsible for the chemical destruction of the passive layer. This can result in red rust deposits. One common source of rouge is the residual polishing debris left inside the striations from mechanically polishing the interior of the tanks or tubing. Electropolishing dissolves this grinding dust so it cannot oxidize and redeposit as Class 1 red rouge.
The other source is erosion of the stainless steel surface by high-velocity water. This also results in Class 1 rouge. Two common sources are: centrifugal pumps and impingement areas from spray balls. Centrifugal pump erosion can come from the impeller tips exceeding the critical erosion velocity and cavitation. Cavitation erosion is common in hot water systems. Sometimes pumps will turn red from the hematite that is carried in the water and is plated out on the pump surfaces.
Figure 5. The same tank after grinding and electropolishing. The pumps were changed and the velocity of the water reduced so the spray balls wouldn’t erode the stainless steel.Spray-ball erosion is more subtle. First, the CIP cleaning systems usually are complex with many spray balls, numerous valves and lots of piping so people tend not to question the calculations. Second, the drilled holes, their pattern and the type of spray ball are the domain of the design engineer. Design of these systems is no easy task, especially calculating the impingement velocity for each jet. Some spray balls can have over 100 holes. This must be matched to the fluid balance determined by the hydraulic engineer. Because of the interdependency of so many variables and designers, and the fact that this has not been identified as a critical item, high velocities can slip by unnoticed — that is, until someone notes the impingement spots on the interior of tanks such as seen in Figures 3 and 4.
Measuring the depth of the eroded spots shown in Figure 3 gave an average value of 0.010 inch and the average diameter of 1 inch. Fifty spots were identified on the dome of the vessel in Figure 3. The volume of metal eroded was calculated to be 0.375 in3. Because there were two spray balls in the tank the total volume of stainless steel removed was 0.75 in3. Keep in mind that this may not be the only system that sees these velocities. Since Type 316L stainless steel is 70 percent iron and Fe2O3 is 70 percent iron, there will be 0.75 in3 of rouge from these two spray balls. If the rouge thickness is 0.001-inch thick it will uniformly cover 5 square feet. The iron would be deposited as red rouge, but the chromium, nickel and molybdenum that are in the removed metal are soluble and may conceivably contaminate the product being produced, although in very minute amounts.
Figure 6. Rouge removal, if done incorrectly, can ruin the surface finish of the vessel and all associated piping. This tank required complete field mechanical grinding and electropolishing. All piping and associated hardware had to be replaced.In this example the flow into the spray ball was 60 GPM or 0.134 ft3/sec. The spray ball had 110 holes 1 mm (0.039-in) diameter for a total of 0. ft2. The tank had two spray balls so the hole area was 0.ft2. The velocity calculated by using the expression Q=AV resulted in an average water velocity of 75.7 ft/sec. The resulting spots are stripped of their passive layer and will continue to corrode until the system is repassivated.
The ASME Feedwater Heater Power Code (asme.org) cites a maximum velocity for hot water in stainless steel of 20 ft/sec. Based on the ASME values for safe operation, these spray balls are operating at nearly four times the maximum velocity.
If the spray ball holes were drilled to 2.0 mm (0.079 in) the velocity would be reduced to 18 ft/sec. This would be a safe velocity and should be more than adequate to clean the system.
In addition, this tank needs to be refinished. This involves grinding the eroded spots to remove all disturbed metal and polishing to a surface finish of 20 Ra (0.5 μ) and electropolishing the ground spots. Then the entire system must be de-rouged, followed by repassivation using citric acid with EDTA (ethylenediamine tetra acetic acid), an iron chelating agent. A word of caution concerning de-rouging: always use a reputable contractor; otherwise your tank may look like the one in Figure 5. In this example, the corrective action involved grinding the entire tank, electropolishing in situ, and replacing all piping, spray balls, valves, and pumps.
Changing the material of construction to an alloy with less iron, such as AL-6XN, 25-6Mo, C-22 or C-276, will result in less red rouge. These alloys are not more resistant to impingement erosion, but the particles will not form Class 1 red rouge.
Spray balls are an essential part of CIP systems. They can be a source of Class 1 rouge if the fluid velocity through the holes exceeds 20 ft/sec. If any areas of impingement erosion are discovered during examination of the vessels then it is an indication that the velocity is too high and remedial action must be taken.
1. "Rouging of Stainless Steel: Why Good Stainless Steel Turns Red," Flow Control, March , Vol. IX, No. 3, Pages 18–24
2. "Get the Red Out – Stop Corrosion in Your Parts Washing Systems," CleanTech, April , Volume 4, Number 4, Pages 22–26
3. "Rouging of Stainless Steel in High-Purity Water," Metals Handbook, Volume 13C, Corrosion, October , American Society For Materials, Materials Park, Ohio
4. "A Stainless Steel Primer, Part 1: The Types of Stainless Steel," Flow Control, August
5. "A Stainless Steel Primer, Part 2: Corrosion Mechanisms,” Flow Control, September
6. "A Stainless Steel Primer, Part 3: Selection of the Proper Alloy," Flow Control, October 200
John Tverberg, principal in the firm Metals and Materials Consulting Engineers, holds bachelor’s and master’s degrees in Metallurgical Engineering and a minor in physical chemistry from the University of Arizona. He was an exchange scientist with EURATOM at Metallgesellschaft, Frankfurt, Germany. Mr. Tverberg is a licensed professional engineer, a Fellow of the ASME, and a member of ASME, ASM International, NACE, and ISPE. He may be contacted at 717 244- or [ protected].
Kermetico HVAF equipment is very efficient in depositing WCCoCr, CrC, Co-based coatings onto ball and gate valve‘s surfaces.
Kermetico HVAF thermal spray systems deposit ductile, high-bond, corrosion-resistant valve coating harder than 1,600 HV300.
We make gas-tight tungsten carbide coatings, impermeable to gas and liquid for pressure ratings of 10,000 psi (690 bar); 15,000 psi ( bar); 20,000 psi (1,380 bar) and 30,000 psi (2,070 bar) without a sealing.
This page shares our experience in wear and corrosion protection of metal-to-metal-seated ball and gate valves.
Ball and gate valves with metal seats provide sealing by metal to metal contact between the gate (ball) and seats.
Sliding of unprotected metals of similar hardness against each other leads to galling. Microscopic bulges on the valve surfaces catch on each other, resulting in high surface friction, heat buildup and plastic deformation. Typically the damage gets worse as the valve cycles until it becomes inoperable.
If no coatings are applied to the trim, galling will be visible almost immediately as the valve is cycled on the test bench. The real service media would increase the wear rate exponentially.
Appropriately selected coatings reduce the friction between the ball (gate) and seats allowing for smooth sliding operation over many cycles, minimizing wear due to galling, abrasion, erosion, particle impact and thermal shocks.
Reduced trim friction lowers the valve’s operating torque. Lower valve torque allows using a smaller, more economical actuator which results in smaller envelope dimensions of the assembly, improves signal response in control service and simplifies selection of accessories to meet cycle speed targets.
Tungsten Carbide is resistant to wear from high cycle operations and erosion from abrasive catalysts, muds, slurries and powders. It is ideal for valves in cryogenic applications, oxygen service and non-lubricative dry gas services. WC-CoCr performs well in hydrocarbon gases and liquids. Carbide coatings offer a low coefficient of friction for ease of valve operation.
Chromium Carbide (CrC) coatings are well suited to very high temperature gas or liquid applications and have excellent resistance to wear, erosion and corrosive media. It performs well in sour (H2S) hydrocarbon gas, high chloride waters, coal liquefaction, catalyst handling and geothermal brine.
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Cobalt-Based alloys often referred as Stellites® (Kennametal Stellite). Particular materials of the class are applied based on their individual properties and suitability for use on different types of parts such as seats, plugs, shafts and bearings.
We use our Kermetico HVAF equipment and technology to deposit WC-CoCr, Cr3C2 and Stellite-type coatings. Even 100 microns (0.004”) of our coating is gas-tight, protecting a valve or seat base metal from corrosive agents as a barrier coating.
Since we have sprayed numerous different ball and gate valves, seats and shafts for both new and repair work in our job shop and none of them have ever been returned to us. They are still in service.
Slurry erosion test, courtesy of Schlumberger.
In this test an Economy mode, Kermetico HVAF WCCoCr coating was compared to a coating of the same material deposited by industry-leading HVOF and detonation systems.
The two following charts are courtesy of the Central Power Research Institute of India.
In these two charts, 5O means the Kermetico AK6 system in HVAF Ultra mode, 5E – AK6 in Balanced mode and 5L – AK6 in Economy mode.
Could the reason for this result be that we are comparing ourselves to less than the best available coating equipment?
You may also be interested in a comparison of a Kermetico HVAF tungsten carbide coating with one of the most advanced HVOF systems on the market.
Are you interested in how our HVAF Balanced and Ultra modes provide such superior results?
As Prof. Wang has shown in his article “Wear and corrosion performance of WC-10Co-4Cr coatings deposited by different HVOF and HVAF spraying processes”:
“Three WC-10Co4Cr coatings were deposited by HVOF and HVAF processes, and their microstructure and properties were investigated in this study. The following conclusions were drawn as a result.
(1) The WC-10Co4Cr coating deposited by the HVAF spraying process exhibited nearly the same phase composition as its initial feedstock powder, which included mainly the WC and some Co3W3C and crystal Co phases with nearly no decarburisation. The JK coating sprayed with Jet Kote III-HVOF equipment exhibited the most severe decarburisation with high-intensity W2C and even metallic W phase. The phase composition of the JP coating deposited by the JP-HVOF system was composed of main WC and minor W2C peaks and exhibited a light degree of decarburisation.
(2) The wear resistance and mechanism of the HVOF/HVAF-sprayed coatings were influenced not only by their hardness but also by their fracture toughness. The high hardness of carbide coating could effectively hinder the cuts caused by the abrasives, and their high toughness could make the binder absorb some of the energy caused by abrasive attacks with some degree of plastic deformation.
(3) The WC-10Co4Cr coatings, which had different degrees of decarburisation, exhibited different dominant wear mechanisms.
(4) The electrochemical corrosion resistances and mechanisms of HVAF- and HVOF-sprayed WC-10Co4Cr coatings were influenced by their phase compositions and microstructures.”
The list price of Kermetico HVAF equipment is lower than the price of a good HVOF system.
With Kermetico HVAF thermal spray systems we are not limited to the “best coating possible.”
We can choose how to spray a tungsten carbide coating:
In addition to coating newly manufactured valve gates and balls to increase their wear and corrosion resistance, Kermetico HVAF coatings on the surfaces of damaged ball or gate valves and seats can be used to return them to their original condition eliminating the need to purchase new parts.
But that’s not the end of the story.
Usually, we deposit coatings using robotic blast and spray operations.
We blast a surface with a Kermetico HVAF gun (it is extremely fast and uniform) and spray with the same gun after switching the powder feed hose and perhaps changing the nozzle
It is much faster, more accurate and consumes much less grit than manual blasting.
It also provides very even surface preparation and induces less stress into the base metal.
Kermetico designs and manufactures three families of HVAF thermal spray equipment.
We create equipment that helps material scientists, engineers and business managers achieve their goals.
We have installed more than 60 Kermetico HVAF systems in the USA, Europe, Japan and China.
Some of the systems are at work in Universities and National Labs, but most of them are used in production thermal spray shops.
We proudly design and produce our HVAF thermal spray equipment in California and install it all over the world.
You can visit our R&D center in Benicia to meet our designers and see our HVAF and HVOF equipment in action.
We also deposit HVAF and HVOF thermal spray coatings onto ball valves for customers in California, USA.
Contact us to discuss your requirements of Electroless Nickel Plate (ENP) Valve Balls. Our experienced sales team can help you identify the options that best suit your needs.