The Optimal Corrosion Prevention Strategy for Your Plant

Improving Lifespan of Pipes and Vessels in Industrial Applications

Download the Form to receive the white paper in pdf format.INTRODUCTION

Corrosion of pipes and vessels poses constant headaches for plant managers and engineers in a number of our most important industries. A handful of specialists now offer a variety of techniques and technologies intended to solve this problem. For the plant manager or engineer who faces a corrosion problem, the choice of the best prevention method can be daunting.

However, many engineers in the chemical processing, oil & gas, and mining industries have already made the choice to use advanced polymer rotational lining. Engineers in these industries work hard to protect plant workers, eliminate unnecessary down time, prevent environmental contamination reduce costs and generally relieve a lot of headaches.

Rotational Lining PipesOne of the more effective strategies for protecting pipes, fittings and vessels in industrial plants is the use of what is today called rotational lining. While there are viable options to rotational lining with an advanced polymer, it is an excellent approach to corrosion prevention. This paper will explore rotational lining as well as its alternatives such as sheet lining, powder coating, dual laminate lining, epoxy coating, glass lining and the use of exotic alloys.

A decision tree can be very helpful for making this type of choice.

DECISION TREE FOR CORROSION PREVENTION CHOICES

Every plant engineer is driven to reduce downtime, particularly unscheduled interruptions. While many plants accept corrosion-related downtime as routine or unavoidable, it can in fact be easily avoided by using the appropriate corrosion-prevention technology. Of the available corrosion prevention strategies, advanced polymer rotational lining in plain carbon steel piping and vessels are the most effective strategies.

The process of deciding how to prevent corrosion in your plant begins by fully evaluating the nature and significance of the problem. The following considerations describe the main factors that drive corrosion control solutions:

  • Are the chemicals being handled acidic, abrasive, saline or otherwise corrosive?
  • Are the chemicals being handled at high pressures or temperatures?
  • Do the chemicals have a long dwell times in pipes or vessels?
  • Are the pipes and vessels generally configured in straight lines with smooth surfaces, or do they include turns, t-shapes and other complex geometries?
  • Is the culture at your company one that invests in preventative anti-corrosion measures, or do they prefer to solve corrosion-related problems as they arise?
  • What corrosion inhibitors are currently used? How effective are they?
  • What would be the financial impact of improving corrosion control? Would reducing corrosion-related costs be minimal or significant?
  • Are corrosible pipes and vessels located in areas where a leak would pose a significant risk to employees or the environment?

Let’s explore the ways that answers to these questions could determine whether rotational lining is a viable corrosion-control strategy for your facility.

COST EFFICACY

Cost

Decisions about corrosion control typically begin, as do most engineering decisions, by exploring cost-efficacy equations. While the cost of prevention is often a fixed cost, the cost of repair can be wildly unpredictable. This cost can depend, for instance, on the pervasiveness of corrosion within the plant, the accessibility of the equipment and infrastructure where corrosion is occurring, and the value of the equipment or the cost of its replacement.

Engineers and executives generally abhor variable costs. If a corrosion problem precipitates environmental contamination, for instance, the company can be liable for a slew of variable costs. The costs to the company in terms of fines, loss of public and investor confidence, and continuing monitoring and oversight by EPA authorities can be astronomical, and of course are additional to the costs of repairing and replacing damaged components of the plant infrastructure.

An important variable cost that is frequently incurred is the use of corrosion inhibitors. If a plant depends on corrosible piping, such as that made from carbon steel or iron, it may also depend on the use of corrosion inhibitors in the media that flow through those pipes.

Rotolined VesselIn addition to this cost, engineers know that chemical corrosion inhibitors are not 100% effective, so even if inhibitors are used, the piping will require replacement at some point. For most facilities that have significant corrosion risk, even those that are adding new construction or are under construction, rotation lining with an advanced polymer is the more costeffective choice.

While the use of exotic alloy piping and vessels can offer some of the same advantages of rotational lining but the high cost and interrupted availability of these alloys make their use prohibitive in most cases. In the rare case that a plant processes a highly abrasive medium, then a very hard exotic alloy might be appropriate. However, the cost, market and technical complexities of using such a metal will relegate it to a very few situations.

In the majority of cases where corrosive media are processed, from fresh water to salt water to a mildly corrosive slurry, to a highly corrosive acid, a rotational lining will protect the facility infrastructure for many years at a reasonable cost.

Efficacy

Efficacy is obviously an essential factor in figuring cost efficacy. A variety of polymers have been used with excellent results in preventing corrosion in pipes and vessels. Epoxies are also used, as is powder coating, sheet lining, glass lining, and fiberglass reinforced plastic lining. Some engineers eschew liners entirely and instead use exotic alloys in pipes, fittings and vessels.

Pipe with Corrosion Prevetive Rotolining ResinsFrom the perspective of efficacy only, rotational lining with an advanced polymer is among the one or two most effective strategies Exotic alloys are in the same conversation – as unsurpassed – as is rotational lining, the alloy lose their luster when cost is considered. Both can be used to prevent corrosion in complex geometries. Both are highly resistant to a wide variety of industrial corrosives. Both are abrasion-, heat-, and impact-resistant and can be repaired.

When cost is considered, exotic alloys become less appealing. Alloys such as 316 stainless steel, Super Duplex, Tantalum or Hastelloy can be prohibitively expensive and can, at times, be difficult to obtain due to variable supply. When cost-efficacy is considered as the essential quality that is desired in an anti-corrosive, then rotational lining becomes the obvious choice.

Efficacy considerations are compared across available corrosion-prevention solutions in the table.

  Rotolining Sheet Lining Powder Coating FRP Epoxy Coating Glass Lining Exotic Alloy
Seamless Liner Yes - Yes - Yes Yes -
Mechanically-bonded Liner Yes - Yes - Yes Yes -
Complex Shapes Yes - - - - - Yes
Thick Liner (>0.188") Yes - - - - - -
Resists Abrasion Yes - - - - Yes Yes
Easily Repaired Yes Yes - - - - Yes
Impact-resistant Yes Yes - Yes - - Yes
No direct internal access req'd Yes - - - - - Yes
Reuse Existing Structures Yes Yes Yes - Yes - -

Table. Technologies currently available for corrosion control in industrial processes.

FLOW MEDIA

The characteristics of the flow media—the material that is carried through the piping and fittings, and contained in the plant vessels—are among the most important factors in choosing a corrosion prevention strategy.

The chemical composition of the flow media must be studied for any possible incompatibilities with potential lining materials. For instance, materials containing aromatic hydrocarbons such as styrene will quickly destroy pipes and vessels made from high-density polyethylene. Conversely, a Teflon liner can withstand prolonged contact with styrene. This is one of the main advantages of rotational lining—it can be done with a wide range of advanced polymers. When Teflon is most effective, then Teflon can be applied. When ETFE will be most effective, then that is the polymer that will be used, and so on. With RMB’s expertise in the use of advanced polymers, the choices are virtually limitless. The temperature range of the flow media must also be considered. Material incompatibilities can vary as the media and liner become hotter. Hot salt water, for example, is more corrosive than cold. Also, the adhesives used to apply some liners can fail at elevated temperatures. Advanced alloys and polymers can be significantly resistant to heat-related corrosion.

Besides chemical incompatibilities between the flow media and the liner material, the potential for mechanical abrasion must be considered as well. Advanced alloys and polymers will be highly abrasion-resistant; however, polymers are not appropriate in cases where significant abrasion by sand or grit is present. In contrast, fusion-bonded epoxy and powder-coated surfaces can also be rapidly eroded by solids and particulates. Corrosion can set in rapidly in elbow and tee fittings if an abrasive medium is piped over powder-coated surfaces.

In some industrial processes, solid particles are a normal component of the flow medium. This type of solid will wear quickly through a fusion-bonded epoxy coating, for example, or a powder coating. This limitation is exacerbated in curved sections of the piping system or sections with nonconstant cross-sectional area, such as an elbow, tee or reducer. These geometries cause turbulence in the flow media, which accelerates wear on exposed internal surfaces. Either rotational lining or advanced alloys are the appropriate solution if a heavily abrasive flow medium is present. Rotationally lined pipes, fittings and vessels can be used for processing the following chemicals and chemical types:

  • Chemical corrosives
  • Acidic materials
  • Acidic processes
  • Brine
  • Chloralkaline material
  • Chromic acid
  • PVC production
  • Sour hydrocarbons
  • Vinyl production
  • Water
  • Mildly corrosive slurry

CONSIDER ALL YOUR MATERIAL OPTIONS

Rotational Lining with an Advanced Polymer

Rotational lining or roto-lining is the most effective way to apply an advanced polymer to a surface where corrosion prevention is the goal. Enlisting the use of roto-molding technology, roto-lining of pipes provides an optimal level of long-lasting protection from corrosive materials for vessels, fittings, flanges and other process equipment. With permanently bonded, seamless coating Pipe Lined for Corrosion Protectionthicknesses of up to 0.45” available in materials such as High-Density Polyethylene (HDPE), Nylon 12, PFA (Teflon), and ETFE (Tefzel), the performance of these systems is hard to match. These heavier liners provide the most durable and longest lasting protection on the market today.

Rotational lining is ideally suited to protect parts with unconventional sizes or shapes. A uniform, seamless polymer layer is bonded to the interior of the metal structure, producing a monolithic, corrosion-and chemical-resistant lining that conforms to complex shapes and is virtually free of stresses.

Fusion Bonded Epoxy Coating

Fusion bonded epoxy coating (FBE) is applied by heating the part and then applying a powdered thermoset resin and hardener to the heated surface. The heated powder melts and flows over the surface, providing a protective coating. When cured, the coating is capable of withstanding high temperatures. However, coating thickness is limited to approximately 0.04”, which limits abrasion and impact resistance and overall durability.

The thin layer of epoxy provides a degree of corrosion prevention when used as a liner in a pipe fitting but its durability is compromised by its minimal thickness. Solid particles in flow media, such as sand, will wear out FBE liners rapidly. This limitation is exacerbated in sections of the piping system that are not straight line and constant cross-sectional area, such as an elbow, tee, or throat. These geometries cause turbulence in the flow media, which accelerates wear on these internal surfaces.

Powder Coating

Similar in application to FBE, powder coating employs a granulated thermoset or thermoplastic powder that is applied electrostatically to the protected surface. The part is then heated in an oven to a temperature that causes the powder to melt and flow over the surface uniformly. Again, coating thicknesses are limited to approximately 0.04”. Powder coating is not a viable approach to complex shapes and geometries, nor is it abrasion or impact resistant.

Sheet Lining and Dual Laminate Lining

These three corrosion prevention strategies share a majority of characteristics. They are useful in limited industrial contexts and share a number of weaknesses that prevent them from being used more universally. For sheet lining polymeric sheets of plastic are applied to the internal walls of a vessel with an adhesive. The sheets typically come in a standard size and must be cut and tailored to the specific dimensions of the part to be lined. Seams between the sheets are then plastic welded together after they have been mounted in place. The costs associated with sheet lining can vary greatly, as it is labor intensive, with costs increasing with the complexity of the part geometry. Maintaining adhesion of the sheets to the protected surface can be an issue, especially at higher working temperatures.

Sheet lining is not limited to steel applications. It can also be used to line fiberglass vessels. The benefit of dual laminate lining is that it can be of use in some limited low-pressure applications. The general limitations enumerated above for sheet lining metal parts apply for fiberglass parts as well. With sheet linings, adhesion to the substrate can be an issue. Joints between sheets have to be bonded, which is time-consuming and makes them prone to leakage.

Loose Lining

Loose lining uses a Teflon or other polymer sleeve that is slid into a pipe or vessel. The liner is flared on the flange faces to hold it in place. These liners can be quite permeable and the voids that typically form behind the liner can allow for chemistry to pool and corrode. This method can be the least costly way to line a smaller diameter pipe, but costs increase significantly as pipe diameters increase.

Glass Lining

Glass lining provides a seamless, mechanically bonded liner that also provides good resistance at higher temperatures. As the name implies, a vessel is coated with ground glass powder and then heated in an oven to a temperature that allows the powder to return to a molten state. The piece is then cooled under controlled conditions, leaving a hard, protective glass surface. The primary disadvantage of this method is that the glass can chip and fracture easily. Even a small crack or chip can result in the entire vessel having to be recoated to guarantee protection. Nonetheless, it provides a hard coating that is well adhered to the pipe wall. Glass coating is a good solution when the flow medium routinely carries an abrasive slurry.

Exotic Alloy

Finally, there is the option of foregoing a protective liner and manufacturing the entire pipe or fitting with a corrosion resistant alloy. Materials such as 316 stainless steel, Super Duplex, Tantalum, or Hastelloy are all metals that offer excellent inherent protection from chemical corrosion. However, the cost per pound of these materials is extremely high and delivery times can be prohibitively long due to limited availability.

CONCLUSION

Rotolined PartsThis thorough examination of the options available for corrosion control in industrial pipes, fittings and vessels is intended to assist plant engineers in deciding on the optimal choice for corrosion control. The cost of corrosion must be considered in the overall view that can include unplanned downtime, repair and replacement of plant infrastructure, the cost of chemical spills, environmental contamination, litigation and safety. Effective corrosion prevention can minimize these costs, keeping the plant and the business on track in the long term.

While there are a wide variety of solutions that an engineer can choose to employ for corrosion prevention, many have limitations in real-world applications. While advanced alloys can be used to create very sturdy and durable pipes and vessels, these alloys are susceptible to chemical corrosion, are very costly and difficult to obtain.

Rotational lining or molding with an advanced polymer is the most versatile of all solutions for corrosion control. It can be used for complex geometries, in pipes, fittings, and vessels. It is highly heat resistant, easily repaired, and highly durable. In any analysis for handling corrosive media, rotational lining and molding with an advanced polymer is the optimal solution.

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