Heat transfer equipment is one of the many important uses of stainless steel, especially in the oil and gas industry. Lead Heat Transfer Engineer at Technip Energies, Paul Miller, spoke with Stainless Steel World Americas about the processes and testing involved with stainless steels, and material selection for heat exchangers.
By Sara Mathov
Paul Miller is a Lead Heat Transfer Engineer at Technip Energies. Based out of Houston, TX, Miller has over 30 years of experience working with various heat transfer equipment technologies and materials. “I work exclusively in the oil and gas industry, including LNG work. With that comes cryogenic temperature services, and of course stainless steels are particularly good for that. Many of the services, including Amine units, are typically all stainless steel construction,” said Miller. “My day-to-day role is designing heat transfer equipment.”
Process and Testing
Miller described the process of putting together a project, and starting development. “Our metallurgist will come in and review the chemical processes. They analyze the chemical compositions and the equipment type for each step of the process,” said Miller. “Operating conditions are also checked to ensure compliance with the specifications.”
Once the process has been analyzed, the project will start coming to life. “They come up with a plan on what metallurgy to use for the piping and equipment,” said Miller. “The engineers, like myself, also have a good feel of what type of equipment should be used, so it is a team effort.”
After reviewing the inspection test plan with the quality department, Miller and his team can flag any areas that they want inspectors to pay close attention to. “Outside of general guidelines, after looking at the plan, we can say that we want more focus on certain aspects of fabrication, or other areas,” said Miller. “The metallurgist and inspection team focus on specific areas, but the engineers are still involved to help identify and solve problems. ”Various data sheets are used with different equipment and materials. “We also create purchase requisitions for the equipment, and solicit bids from vendors. Then we review the bids, select the technically acceptable vendors, and then the procurement department selects the vendor from the list of technically acceptable vendors to issue the purchase order to,” said Miller. “Then, we follow the fabrication guidelines, and review the drawings and calculations that come from the vendors.”
“Our company has an approved vendors list, but our clients who are funding the project usually have their own preferred suppliers. The client’s and our procurement departments will get together, compare the lists, and select the group of vendors that will receive a bid package.”
Transition of Materials
Stainless Steels have been able to improve and replace other metals. “For example, in cooling water service, traditionally it relied on copper alloys. But for heat exchanger tubes, copper became very scarce and expensive,” said Miller. “Then, in response to this, duplex stainless steels came into the market, and offered a superior and cost effective replacement material.”
“Duplex stainless steel has both austenitic and ferritic properties. The austenitic properties can be undesirable with cooling water because of the chloride in the water. But steels that exhibit ferritic properties are not bothered by it. Now, older plants are making a big push to replace the old copper alloy heat exchanger tube bundles with duplex stainless steel tube bundle components.” Miller said duplex stainless steel is almost exclusively used now in heat exchangers in cooling water service.
Causes of Failure With Stainless Steel
Miller recalled a time where failure occurred with stainless steel in a steam methane reformer. “Inside of SMRs are basically big stainless steel tubes that feed the reactor tubes in the radiant section. An economizer is used to preheat the feed that goes into the tubes, and operates at a very high temperature,” said Miller. “It is so high that it is above the transition range for stainless steel.”
“One day, one of the operators handed me a piece of piping, and when I asked what it was, he said it was stainless steel. It did not look anything like stainless steel. What had happened was, the operating temperature was above 1150 degrees Fahrenheit, and the metal became sensitized. Chromium is what gives stainless steels corrosion resistance, and when in operation at the high temperature for extended periods of time, it loses its ability to inhibit corrosion and basically turns into carbon steel.”
Miller stresses that analyzing failure is so important, because in this case, it was not the material chosen but the environment. “Right outside of this plant, there was another plant making pool chemicals, with chlorine and chlorides,” explained Miller. “You have a metal that is no longer providing protection against corrosion, in a very corrosive environment. All of the piping was completely corroded after the metal became sensitized. Replacing all of this stainless steel was quite a project, but it had to be done to ensure that the equipment could be operated safely.”
Looking Ahead and Sustainability
Miller described that the company is very committed into moving forward with transitional technologies and sustainability. “They call it sustainable chemistry. For example, we may partner with a company that specializes in biological transformation of waste into useful chemicals, such as ethanol. Our company could take the ethanol and convert it into ethylene. In effect, you have what would be called a green plastic as the result,” said Miller.
Miller said the most impactful energy transition he foresees is moving towards methane and LNG. “We have already seen a huge reduction in the US in our carbon footprint, with the shift from coal plants to natural gas fi red plants,” said Miller. “It is not technically fully green, but it is doing a tremendous job in reducing the amount of carbon that is emitted into the atmosphere.”
Going forward, Miller said hydrogen is still important alongside other technologies. “There are other technologies that can also be taken advantage of, to get us even further into circular economies,” said Miller. “One is called the Fischer-Tropsch process. This takes syngas, a mixture of carbon monoxide and hydrogen, and converts it to hydrocarbon fuels, except it builds the molecules up one carbon atom at a time. This creates fossil fuel analogues that have zero impurities in it, there are no sulfur compounds, or aromatic compounds. The route to deriving the syngas can be varied. Biomass waste can be converted into syngas by gasification, and feeding that same gas into a Fischer-Tropsch reactor to produce new fuels. So, it replaces on a one-to-one basis fuel that would normally be created with fossil fuels.”
“The improvement in carbon efficiency has not been linear. Artificial Intelligence has led to vast advances in catalysts and this is allowing the decarbonization of chemical processes at a nearly exponential rate. With advancements in areas such as new alloys, nanotechnology, AI and new materials, graphene for instance, many paths will be taken on the way to better green energy solutions,” said Miller.