^ A tube sheet being cleaned. Photo: Hammelmann
Article by David Sear
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Top row from left to right: Arjan Woerden, Shell, The Netherlands; Willem Maarten van Haaften, Shell, The Netherlands; Barinder Ghai , Sandvik, UK; bottom row from left to right: John Butterfield, KCI Publishing, The Netherlands; and Bernardo Siza Vieira, Sandvik, Portugal.
Background
The workshop was a collaborative effort from Barinder Ghai and Bernardo Siza Vieira (both Sandvik Materials Technology), together with Shell’s Arjan Woerden and Willem Maarten van Haaften. The meeting was facilitated by John Butterfield (KCI Publishing). Barinder acted as moderator, inviting expert comments from Bernardo, Arjan and Willem Maarten whilst ensuring all participants had ample opportunity to raise questions and contribute to discussions.
Presentation structure
The heart of the workshop was formed by three top-level topics: 1) what are the current challenges with heat exchangers? 2) What are the factors influencing upgrading from low alloy to duplex stainless steels/high-nickel alloys? 3) What are the current limitations when upgrading? For convenience, each topic was further broken down into a series of short questions. This write-up follows the same structure, presenting comments from the panel and audience per topic and per question.
Topic one: what are the current challenges with heat exchangers?
1: Quality assurance
- “My company has well-defined Design Engineering Practices which nicely indicate relevant QA issues. However, I wonder whether others in the supply chain have access to equivalent details.” End user
- “Do end users sometimes rely too much on accrued knowledge? Using internal standards drawn up in the 1950s can be a major hindrance.” Consultant
- “I am often submerged under quality documents submitted by end users. They take a long time to sort through with many proving irrelevant. End users should indicate which quality documents are applicable and which are not.” Tube supplier
- “Why can’t I speak directly to end users? I often have to work via three or four intermediaries in the chain, which unnecessarily complicates getting answers to questions.” Primary product supplier
- “Heat exchangers are not commodity products. I recommend that everyone involved should check all details in advance.” Fabricator.
- API standards are my starting point. If a tailor-made product is needed I discuss critical issues with the manufacturer and we jointly modify the standard specifications. My tip to ensure heat exchangers work as expected is to buy from a reliable manufacturer to start with. And even then you must pay close attention to quality control!” End user
- “For us it is equally important to visit pipe mills regularly and to perform our own quality assurance checks.” Heat exchanger manufacturer
- “A lack of regular inspection and cleaning can lead to many heat exchanger problems. Maintenance crews used to inspect equipment much more regularly, at the same time cleaning the tubes and conducting small repairs. With today’s risk based inspection there is an assumption that heat exchangers are working fine. The only people who ever see them regularly are the process technicians and they have not been told to conduct inspections let alone cleaning!” End user
2: Fabrication issues
- “There are sufficient documents explaining how to weld even the most exotic of alloys; it is simply a question of applying them.” Fabricator
- “Time is often the critical factor. In a process facility we need to replace leaking heat exchangers right away. A lack of time for planning is a feeding ground for problems.” End user
- “We purchase equipment for end user clients using a policy of zero based execution. Hence we refer to industry recognized standards such as ASME and NACE for heat exchangers, impressing on end users that putting their own extra standards to one side helps to get a quality product in the required timeframe.” EPC
- “Globalisation is driving many fabricators to invest in novel technologies that promise to be faster and cheaper. If there is no time to iron out the teething problems in new technology that can create headaches later on.” Heat exchanger manufacturer
3: Operating conditions
- “In addition to the standard operating conditions you should also consider upset conditions, possible fouling and also feed flexibility. So materials engineers must never work in isolation but should always be talking to process engineering, the project department, the fabricators and the inspector.” End user
- “Designing a heat exchanger which will meet future needs is a real challenge, and it can be hard to justify extra outlay for more exotic alloys.” End user
- “Thirty years ago heat exchangers were either carbon steel or rusty carbon steel! Now even duplexes are being specified, often simply as a way to keep process systems up and running. For a new grade is to be commercially successful parties in the supply chain must cooperate to ensure the ready availability of all the standard products that could be needed.” End user
4: Life cycle costs
- After identifying corrosion in a heat exchanger I proposed three or four solutions, including renovation and upgrading. All were perceived to be too expensive! People holding the purse strings simply don’t look at the long term.” End user
- “What should be included during life cycle costing? Conducting inspections every three months could be costing EUR 280,000 per year! Factor that in and the case for investing in a corrosion resistant alloy is more easily made.” End user
- “If your carbon steel product is failing every two to three years then it is definitely time to consider stainless steel.” End user
5: Material selection
- “Issues which are important are surely costs, corrosion issues and thermal properties.” Tube manufacturer
- “Not all fabricators seem to know how to correctly weld or pickle certain alloys.” End user
6: Availability of product forms
- “2205 duplex in all product forms is easily obtained in Western Europe, making it suitable for grassroots projects. The position can be very different in Asia and the US.” End user with global responsibilities
- “In Europe you can find good fabricators such that a 2205 duplex heat exchanger is price competitive to 316 stainless steel and can be delivered in under three months. Alloy 59 heat exchangers can also be obtained but take from six to eight months. That is not likely in the United States.” End user
- “Finding tubes is easy; locating tube sheets in exotic alloys is the issue. Instead of a forged tube sheet I will often accept a cast alloy plate or a carbon-steel plate with a corrosion allowance.” End user
Tube sheet welding in progress.
Photo: POLYSOUDE1
Topic two: factors influencing a potential upgrade from low alloys to higher alloys
1: Why upgrade?
- “The timescale is key. If a refinery is to operate for another fifty years the case to invest in nickel alloys is easier to make.” End user
- “In addition to solving corrosion problems, upgrading to higher alloys can help increase your operating window and feedstock flexibility.” End user
- “Environmental concerns are also a reason to upgrade to duplex stainless steel. Take closed cooling water systems where chemicals are used to maintain water quality. Leaks need to be prevented to ensure no chemicals are released into the environment. In such cases my managers agree to using duplex for heat exchangers with no questions asked. The same applies if there is even the smallest chance of hydrocarbons entering the environment.” End user
- “In the food and dairy industry our concern is to prevent leaks from contaminating a product destined for human consumption.” End user
2: Issues with life cycle costing
- “If life cycle costs are correctly calculated then higher alloys can save money in the long run. The challenge is to change people’s mindsets. I have seen inspection teams still checking Alloy 625 heat exchangers even though we tell them that these items are designed to run without maintenance for longer periods of time. It is therefore important to record experiences with new alloys and build up a trust base so that future inspections can be scaled back.” End user
- “Beware also of phantom damage. Inspection sometimes suggests that tube walls have thinned slightly, but such local thinness can also be due to manufacturing intolerances.” End user
- “Life cycle costing is based on current knowledge and does not consider future changes. Take the catalysts being developed to widen the operating window of existing facilities, enabling more contaminated feed stock to be accepted. We have no idea what effect this could have in terms of corrosion.” End user
3: Weight savings
- “Using duplex can save weight which is handy for offshore facilities but less interesting onshore and especially in replacement situations where the civil structure is already in place. Nevertheless, using duplex can make sense for modules built overseas requiring transport to the jobsite.” EPC
- “With duplex you can use thinner walled tubes which makes welding easier and reduces labour costs.” Fabricator.
- “To replace a heat exchanger the simplest option is a like-for-like replacement. In addition to alternative alloys you can also consider different designs, such as spiral or plate heat exchangers.” End user
4: Energy transition
- “New alloys can surely help generate more efficient heat exchangers.” End user
- “The alloy chemistry can be tweaked to improve heat exchanger efficiency. However, shorter lines are needed between all parties to create synergies.” Supplier
- “The new generations do not want dirty technology. My children are already now quizzing me about my work in a refinery and why we have not yet bought an electric car. We all recognize the need for change, but the question is, who is going to take ownership of this change.” End user
A dismantled plate heat exchanger.
Photo: RomanM82
Topic three: current limitations when upgrading
1: Budget constraints
- “Financial issues are certainly a constraint to improving heat exchanger designs but a bigger hurdle is that none of my customers wants to be the first to try new technologies.” EPC
2: Lack of experience / references
“Carbon steel and low alloy steel are no longer the standard material for heat exchangers in refineries but a new standard has yet to be determined.” End user
3: Lack of competitive fabrication
An advantage of plate heat exchangers is that no welding is required.” EPC
4: Other aspects
- “Companies in Asia seemed more motivated to upgrade materials than their counterparts in Europe. But as always plant profitability at the time investments are needed is key.” End user
- “Government action can also drive change. For example, the Dutch government is promoting the use of geothermal energy to warm houses. That could create a huge increase in demand for plate heat exchangers.” Consultant
- “Plate heat exchangers can be prone to carbide corrosion, so can that be solved by improvements in materials and design.” End user
- “When helping the environment you must consider the broader picture. Adding vegetable oils during diesel production can cause future corrosion issues.” End user.
- “If change is too fast some groups may feel disenfranchised.” End user
- “Heat exchangers have long been in existence but this sector is and will remain diverse and full of challenges!” Tube supplier
Take-aways
After the workshop, the panel agreed that the following key conclusions/recommendations could be drawn from the session:
Increase efficiency
- Effectiveness can be gained by having suppliers, fabricators and end-users talking to each other at an early stage, especially when using new or higher grade materials
Promote high-grade materials
- The application of high grade materials is difficult from a cost perspective. Addressing the full life cycle of heat exchangers could help although high grade materials will always be more expensive in the short term
- Best way forward for industry is to jointly review the issues with heat exchangers with a shorter life cycle (requiring replacement every two to three years) and together to select the Next Best Alternative that enhances the life cycle with limited impact on the long term cost
- Innovation and new material development for heat exchangers is key and requires more input from end users /EPCs, such as in joint industry projects
- A cost effective material is required that lies between austenitics/duplex and high-nickel alloys which would help reduce the overall cost of the heat exchanger and subsequent project
Reduce variability during upgrades
- The sheer number of variables to take into account when considering upgrading a carbon steel heat exchanger can paralyse the project. In the current global climate, the key is to start from like-for-like replacement and consider three variables only:
- Life-cycle cost for a higher grade material (including necessary inspections needed when replacement is like-for-like)
- Better efficiency/reduced carbon footprint for a higher grade material (energy transition)
- Increased operating window flexibility for a higher grade material.
Consider alternative designs
- It is vitally important to take a broad perspective when upgrading/replacing shell and tube heat exchangers. The best option could be to replace a shell and tube heat exchanger with a spiral type or plate type heat exchanger, with or without a material upgrade
- The question should always be asked: “what if I could design this heat exchanger from scratch”?