Stainless Steel World Magazine April 2024 | Page 46

ASM Metals Hand Book

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 .

Material selection for heat exchanges 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 . 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 , highalloyed 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 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 .

Properties Stainless steel 310 / S products are nonmagnetic 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 hightemperature applications . The lower carbon content of 310S minimises 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 sensitisation in service . The high Cr and Ni content make these steels suitable for applications that reduce sulphur atmospheres containing H2S . Both are

Stainless steel tubes

widely used in moderately carburising atmospheres , as encountered in petrochemical environments . For more severe carburising atmospheres , grade 310 is not recommended for frequent liquid quenching as it suffers from thermal shock . The grade is often used in cryogenic applications due to its toughness and low magnetic permeability . Similar toother austenitic stainless steels , heat treatment cannot harden these grades . They can be hardened by cold work , although this is rarely done in practice .

Grade 310 / S for heat exchangers While designing and constructing heat exchangers , it is necessary to satisfy the multilateral and often contradictory requirements as far as possible . The main issues are compliance with the conditions of the technological process , a possibly higher heat transfer coefficient , low hydraulic resistance , resistance of heat exchange surfaces against corrosion , accessibility of the heat transfer surface for cleaning , manufacturability of structure from the point of view of fabrication , and the economical use of costly materials . This final point requires the consideration of factors including : 1 . Fabrication characteristics – Stainless grades 310 and 310S rolled pipe , tube , plate / sheet in bent condition , and any forged component can be fabricated by cutting the products as designed , as

Composition % C Mn Si P S Cr Ni

Stn310 0.25 max 2.0 max 1.5 max 0.045 max 0.030 max 24-26 19-22

Stn310S 0.08 max 2.0 max 1.5 max 0.045 max 0.030 max 24-26 19-22

Tensile strength - 520MPa min , Yield strength - 205 MPa min

% Elongation – 40 Hardness -205 BHN

Table 2 . Chemical composition & mechanical properties ( primary alloying elements being Cr & Ni )

PREN 25 , & in Sea water 22 similar to 316 grade

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