From his office in Amsterdam where he helps Fluor build refineries and chemical plants, Mr. Rensman tells us that what he loves about his job is the very diverse and challenging environment in which he works, with never two days the same. He is employed as part of a team of four, each of whom is a certified International Welding Engineer (IWE).
Leaving the University of Twente, The Netherlands, with the equivalent of a M.Sc. degree in Mechanical Engineering and a major in Materials Science, he originally went to work for a nuclear service provider in Petten, The Netherlands, on applied materials research for structural metallic materials in nuclear applications. What this entailed was testing neutron-irradiated materials for changes in mechanical properties after irradiation. His specialty was fracture behavior and fracture mechanics of structural steels, stainless steels, and nickel-based and aluminium alloys. After ten years, he joined Fluor and took part in the IWE education program at the University of Utrecht, The
Knowledge as a tool
“It is one thing to study at university and another one entirely to put theoretical knowledge into practice,” he wisely tells us. “I am a great believer that the real learning school for engineers is in live practice where you actually see materials that fail, degrade, corrode, and break. Nothing can beat it for enhancing knowledge skills and experience. Fortunately though, I also have some very good and knowledgeable colleagues at Fluor with a great deal of experience to rely on. As a company, we also have an experienced network to draw on all over the world and a community of material welding engineers in which we regularly share information each month in teleconferences.”
“Over the years, I feel that my job and its decision making capabilities has increasingly become more important as knowledge and experience related to the quality of fabrication, pressure equipment, and heat exchangers have declined in other organizations. Most people are able to follow code specifications when manufacturing or requesting products, but a code is not a cookbook. You really have to build up your own understanding and experience on what works and how to manufacture things, in addition to following code guidelines. This is particularly important when it comes to selecting materials for explicit equipment, and is especially true of work for refineries and chemical processes. We at Fluor try to provide our clients with the optimum solutions for their capital investments with the most cost-effective materials for the application. We are convinced that we have the staff with the appropriate knowledge basis to make the correct judgements.”
“The bottom line is that quality control should always be key, even in these extremely competitive times. If you ensure this, then it is possible to purchase equipment anywhere in the world.”
Special interests with regard to heat exchangers
Mr. Rensman’s interest in heat exchangers comes partly from the perspective that they are an integral part in most process installations and refineries and, as such, play a key role in their performance. Energy conservation is a very pertinent topic nowadays, of course. Additionally, due to their intricate construction in bringing two process flows very close together to allow heat to be exchanged, there is always an inherent risk that these flows come into contact if the thin wall between them fails because of degradation, corrosion, or fracture. These are his daily tasks – the selection of fit-for-purpose materials, to verify that design codes are met for these materials, and that recognized industrial practice fabrication techniques are followed to ensure that they can be used safely and efficiently.
“These tasks are an inter-disciplinary effort between thermal design engineers, mechanical engineers, welding engineers, and vendor and end-user counterparts. Only then can the integrity of equipment be guaranteed. This approach is important to ensure that all aspects in the process chain are covered. For example, sometimes equipment is manufactured correctly but then stored unsuitably, for instance when stainless tube bundles, once produced, are stored but left exposed to a salty, corrosive atmosphere.”
A myriad of heat exchangers to handle
Mr. Rensman has to deal with a myriad of heat exchangers in his daily work of which shell and tube heat exchangers are the most common. Nevertheless, he is also confronted with challenges arising from air-cooled, plate and frame, compablocs, tube-in-tube, and hairpin heat exchangers, to name a few.
“There are so many designs in use, and each heat exchanger has to be built to fit the needs of a specific application. In Amsterdam we have a very good team that we can rely on for selecting the appropriate heat exchangers and performing the thermal design. Nevertheless, they regularly discuss with people like me how to fabricate certain details or to double check manufacturer proposals. I will check fabrication and NDE procedures, particularly when related to the engineering and manufacturing stages at the vendor shops. Moreover, whenever problems arise and repairs are required, I review these for acceptance.”
“Over the years I have seen instances where failures have occurred – like when cracks have appeared in duplex components because the phase balance in the metal was not correct. When failures occur, I will regularly discuss them within Fluor’s group of welding materials engineers to see if we need to change our practices or change our advice to industry on certain applications. Likewise, we pick up valuable information from our clients in the same way,” adds Mr. Rensman.
“In Amsterdam we mostly work on projects dealing with grassroots or new-build refinery and chemical units. Because we deal with such a variety of heat exchangers, we use many different materials as well – anything from work horses like carbon steels and the 300 series of stainless steels, right through to low-alloy nickel and chrome-moly materials, nickel-based alloys, but also aluminium, zirconium, and titanium alloys. For every application, there is a material. Although we generally use regular grades, exotics are used in special circumstances. A good example would be the frequent use of titanium grades or super duplex for seawater cooling service. In the chemicals industry we typically deal with lower pressures, but the substances being handled can be challenging since they are aggressively corrosive. In these circumstances, we will often choose to use the highest grades available in terms of materials, like nickel-based alloys. They are naturally very expensive but are necessary to withstand the destructive corrosion from the chemicals. To choose cheaper materials would not be cost effective as their lifecycle costs would be very high as a result of frequently required replacements.”
Case studies with welding heat exchangers
“Each design of a heat exchanger has its own challenges. For certain applications, as is to be expected with the emergence of new materials and technologies, some very specific problems have come to light. There have been serious failures in the last decades with duplex air-cooled heat exchangers in high-pressure hydrogen and wet hydrogen sulphide service in reactor effluent air coolers. Fluor has moved away from duplex in these applications, as advised by the technology providers for hydro-processing units.”
“Other problems are still often related to the tube-to-tubesheet joint, and many fabricators are struggling with the phase balance still to this day. The tube-to-tubesheet joint remains one of the most fragile joints in the system, and is often the first to fail. Proper qualification remains key here. Practices like API 582 contain additional details for necessary tests to be included for duplex welding qualifications. There have, furthermore, been instances of improper heat treatment for duplex, which is always a concern. Developments like manufacturer qualifications according to Norsok or material testing requirements like ISO 17781 for the control of the microstructure are increasingly being required by end users today.”
“As you see, my work is always an ongoing process of learning, which adds to the fascination of working in an industry and providing the best solution possible to a client,” concludes Mr. Rensman.