Aggressive operating conditions aggravated by high temperatures can have life limiting effects on tube materials, explains ManabHalder of Sandvik Materials Technology.
Tubes specifically for high temperature applications are used across a range of industries in furnaces, recuperators, muffle tube furnaces as well as thermocouple protection tubes, radiant tubes, tube hangers in petroleum and steam boilers, burners, blast furnaces and lime lances in the steel industry. In such high temperature operations, structural stability along with high quality materials and continuity of supply are prerequisites to good performance and increased lifecycles of the seamless tubes.
As part of the’Make in India’ initiative, the company is now manufacturing Sandvik TP310S/H high quality, stainless chromium-nickel steel seamless tube for high temperature applications at its advanced tube production unit in Mehsana, Gujarat.
The world class extrusion press and cold pilgering line ensure production consistency of high quality seamless tube to exacting standards. This provides an indigenous and completely reliable source of high temperature tubes for the Indian market as well as continuity of supply for the Asian Pacific sector. Having a local production facility not only means consistent high quality, but also reliability of supply so essential for manufacturers when they need tube material quickly.
Sandvik’s extensive knowledge and supply of high temperature tube means we can offer optimized solutions when it comes to corrosion resistant properties and high temperature strength in order to maximize service life.
Integrated production and quality control throughout the entire tube manufacturing cycle at Mehsana ensures complete material traceability and uniform tube quality every time.
Complementing the local production facility Sandvik’s technical specialists are available to advise on material suitability given complete details of the manufacturing environment, operating temperature and presence of corrosive agents where the high temperature tubes are to operate.
The unsurpassed level of material consistency offers customers productivity advantages as they can rely on the quality and performance of the seamless tube from Mehsana so there is no operational fluctuation from batch to batch. This means that, unlike some other sourced tube materials where performance characteristics can be unknown, each consignment of Sandvik tubes maintain consistent operational performance and reliability.
An austenitic, stainless chromium-nickel steel of the 25/20 type, Sandvik TP310S/H, the chemical composition of which is shown in Table 1, is suitable for high temperature applications providing good resistance to carburization, sulphidation and oxidation combined with moderate creep strength and structural stability. It has a maximum service temperature in air of 1100˚C.
The seamless tubes are available in a range of diameters from 15.88 mm to 65 mm and in wall thicknesses of 2.31 mm to 12.5 mm in accordance with ASTM/ASME A312/SA312, A213/SA213 specifications, including testing. Produced by the extrusion process followed by cold pilgering, the result is a high quality and consistent seamless tube with good structural stability.
One particularly demanding application is for muffle tubes used in wire drawing mills on furnaces for heat treatment. The muffle tubes shield the wire from the aggressive environment of the furnace creating ideal conditions for a more even temperature distribution. High operating temperatures can result in a short service life, leading to frequent stoppages for maintenance and muffle tube replacement.
Operational experience
One wire manufacturer in India was experiencing just such operational problems within the wire annealing furnace caused by limited life expectancy of the muffle tubes. Not performing to expectations the high temperature tubes, which were sourced externally, were only lasting 3-4 months, resulting in productivity disruptions and unpredictability. Sandvik specialists reviewed the operational and environmental conditions and in consultation with the customer recommended installation of Sandvik TP310S/H muffle tubes. Following installation the results proved to be even better than anticipated with the high temperature tubes providing, on average, over three times the service life of the original tubes. Also proving beneficial to the operation is the repeatability of the material assuring the customer that the muffle tubes are always of exactly the same consistency from batch to batch. Something they could not rely on previously. What was also significant for the wire mill was that the manufacture and supply of the muffle tubes was local from Sandvik’s advanced tube production facility in Mehsana.
Sandvik TP310S/H high temperature tubes from Mehsana are also being supplied for the production of pyrometer tubes to the mineral insulated cable industry for the production of highly sensitive thermocouple protection tubes.
Here it is imperative that the protective tube is of the finest quality in order to ensure consistency of production. As part of the manufacturing process the seamless tube is further reduced being drawn down to the required sizes for the pyrometer tubes.
Any inconsistency in the material could results in rejection of the product as it would not be compatible with the precision requirement of precise temperature measurement. That is why it is essential for manufacturers to have a local, reliable and permanent source of consistent, repeatable, high quality tube material to meet their requirements.
The thermocouples are used in a variety of applications where exact measurement and control of temperatures is essential in processes such as metal production, glass manufacture, petrochemical industries, cement processing and food and beverage industry. In certain applications, the tubes can be exposed to corrosive gases or liquid metals at high temperatures without cooling. Here it is essential that the tube protects the thermal sensor from the hostile environment as any loss of temperature control can jeopardise both the manufacturing process and the associated equipment.
Prevailing conditions
Key to selecting the correct steel grade is a full understanding of the actual environmental conditions that exist around the manufacturing process. Unscheduled shutdowns can result in major production losses so selecting the right high temperature tube material in the first place can eliminate this scenario.
Many of our customers are putting more and more emphasis on reduction of downtime to improve production output, stability and profitability. Of course, being able to source quality, high temperature tubes manufactured locally in India is a distinct advantage and our customers certainly appreciate with operational life of the tube, in many circumstances, being doubled. While a high temperature alloy tube may appear more expensive increase in the lifecycle performance and related productivity more than offsets any perceived increase in cost for the higher performance tube material, as the wire mill case study clearly demonstrates.
