Special Topic
Modern Petrochemical Heat Exchangers in AISI 310
Heat exchangers transfer thermal energy in both heating and cooling processes . Due to the wide variety of processes in the chemical and petrochemical industries , knowledge of the materials used in the design of heat exchangers is of paramount interest to fabricators .
By Srikumar Chakraborty – ex ASP / SAIL
Heat exchangers transfer heat between media , which may be a gas , liquid , or a combination . Fouling undermines heat exchange efficiency . Corrosive fluids associated with intensified fouling may be due to the selection of improper or sub-standard materials , design flaws leading to variable heat transfer , flow resistance degradation , and drops in pressure .
When designing the thermal and mechanical properties of heat exchangers , reputable manufacturers consider process characteristics such as fouling rates and the acidic corrosivity of fluids , taking guidance from their Research & Development team .
Heat Exchanger Equipment
Heat exchangers are widely used in the petrochemical , chemical and refining industries where chemical technology processes ( evaporation , rectification , drying , and more .) are associated with the need for heat supply or removal .
Physical Properties – High heat transfer coefficient ( requiring high thermal conductivity for tube and pipe material ), as low thermal expansion coefficient as possible considering the materials used for tube and sheet plates , tube support and shell to provide resistance to thermal cycling .
Mechanical Properties – Good tensile and creep strength properties ( high creep rupture strength at the highest temperature of operation and adequate creep ductility to accommodate localized strain at notches ), and good fatigue , corrosion fatigue and creep-fatigue behaviour . Most austenitic stainless steels with a chromium ( Cr ) content of at least 18 % can be used at temperatures up to 870 ° C , while grades 309 and 310 can tolerate temperatures up to 1150 -1200 ° C . The high fracture toughness and impact strength of grade 310 means it has good resistance to fractures . The low corrosion rate minimizes the corrosion allowance required . Grades 309 and 310 also offer corrosion resistance to abnormal chemistry , which may result from upstream leaks or chemistry control failures resulting from a mix-up of shell and tube fluids .
Grade Intermittent Continuous
304 870 925 309 980 1095 310 1035 1150 316 870 925 321 870 925
Table 1 . Maximum Service Temperature (° C ) In Austenitic Grade Stainless Steel . Courtesy : ASM Metals Handbook .
Material Selection for Heat Exchangers
A general procedure for identifying the most appropriate material for a heat exchanger application would consider the following :
1 . Requirements of the heat exchanger . 2 . Strategy evaluation . 3 . Raw material selection . 4 . Cost calculation .
While an assessment of costs for any equipment breakdowns or tube replacement should be considered , the raw material selection factors affect the performance of the heat exchanger . strength , corrosion resistance and stability at elevated temperatures .
Heat exchangers manufactured from stainless grade 310 are used for cooling and heating processes in space heating , refrigeration , air conditioning , power stations , chemical plants , petrochemical units , petroleum refineries , natural gas , heat treatment furnace parts and sewage treatment .
A classic example of a heat exchanger is an internal combustion engine in which a circulating fluid known as engine coolant flows through radiator coils . Air flows past the coils , which cools the coolant and heats the incoming air . Another example is a heat sink , a passive heat exchanger that transfers the heat generated by an electronic or mechanical device to a fluid medium , often air or a liquid coolant .
Heat exchangers account for over 30 % of the total market share of petroleum and chemical products requiring heating , cooling , or condensation processes . They play an essential role in product quality and process economy by utilising heat . The trend is for heat exchangers to develop towards large-scale , high-efficiency , high-alloyed products with low-temperature difference and low-pressure loss . In many situations , particularly offshore and remote locations , heat exchangers can be configured to provide maximum heat transfer for a minimal footprint while maintaining safety .
Although stainless steel grade 310 is subject to stress corrosion cracking , it is more resistant than grades 304 or 316 . It has good resistance to oxidation in intermittent service in air at temperatures up to 1040 ° C and in continuous service at 1150 ° C . It also has good resistance to thermal fatigue and cyclic heating , exhibiting remarkable flexibility , durability , toughness , high tensile
Properties
Stainless steel 310 / S products are non-magnetic as annealed and become lightly magnetic if cold-worked . The difference between grades 310 & 310S ( described as a low-carbon version of 310 ) is the carbon content . Both grades are used in high-temperature applications . The lower carbon content of 310S minimizes carbide precipitation and improves weldability . The mechanical properties for both grades are the same .
Both grades contain 25 % Cr and 20 % Ni , making them highly resistant to oxidation and corrosion . Grade 310S is less prone to embrittlement and sensitization in service . The high Cr and Ni content make these steels suitable for applications that reduce sulfur atmospheres containing
H 2
S . Both are widely used in moderately carburizing atmospheres , as encountered in petrochemical environments .
Stainless steel tubes .
6 Stainless Steel World Americas - August 2024 | www . ssw-americas . com