Stainless Steel World Americas August 2024 | Page 7

For more severe carburizing 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 to other 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 these grades can withstand working temperatures in the range of 975-1175 ° C . Heavy work is carried out down to 1050 ° C by standard methods and equipment .

2 . Machining – the machinability of grades 310 and 310S is similar to that of grades 304 and 316 . Work hardening can be a problem , and it is customary to remove the work-hardened layer using slow speeds and heavy cuts with sharp tools and good lubrication . Powerful machines and heavy , rigid tools are used .

3 . Weldability – Grade 310 / 310S products in any shape are a great way to connect two pieces of metal and have many advantages over other welding methods . Grade 310 is corrosion and heat-resistant , does not require a heat treatment step , and can be welded using various welding equipment . It is also ideal for projects that involve environmental protection and safety aspects .

Stainless 310 / 310S grade is welded with matching electrodes and filler metals . Products are readily welded by standard welding manuals using techniques such as GMAW ( MIG ), GTAW ( TIG ) and SAW . Preheat and post-heat are not required , but post-weld solution annealing is essential for corrosion service in liquids . Pickling and passivation of the surface

Figure 1 . Sectional View of A Heat Exchanger .

Stn310s 0.08 max 2.0 max 1.5 max 0.045 max 0.030 max 24-26 19-22

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

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

to remove high-temperature oxides are necessary to restore complete aqueous corrosion resistance after welding . This treatment is not required for high-temperature service , but welding slag should be thoroughly removed . Grades 310 / 310S are solution annealed by heating to 1040- 1065 ° C , holding at temperature until thoroughly soaked , then water quenching .

Design And Fabrication

The primary function of heat exchangers in the petrochemical industry is solvent condensation undergoing chemical cooling and heating reactors . The design of the equipment is based on temperature ranges , product mix , pressure drops across the exchanger , fluid flow capacity , cleanability , repair and maintenance .

Seamless or welded tubes of suitable materials are used without compromising quality during manufacture .

Fouling Problems – Cause & Remedy

Fouling is a membrane separation phenomenon resulting from several mechanisms : precipitation of sparingly soluble salts , adsorption , cake or gel formation , and pore blockage because of the composition of the water in the system , causing a decrease in the heat transfer coefficient with time . Klarex ’ s ( Netherlands ) self-cleaning heat exchanger consists of a design that reduces the surface area by approximately 20 %.

Scaling occurs because the water flowing through the heat exchanger contains impurities such as calcium carbonate , magnesium , chloride or iron . Fouling represents the theoretical resistance to heat flow due to a build-up of a layer of dirt or other fouling substance on the tube surfaces of the heat exchanger .

A method for reducing the formation of deposits on the inner walls of a tubular heat exchanger through which a petroleum-based liquid is flowing comprises applying fluid pressure pulsations to the liquid flowing through the tubes of the exchanger and vibration to the heat exchanger to affect a reduction of the viscous boundary layer adjacent to the inner walls of the tubular heat exchange surfaces .

Reduction of the viscous boundary layer at the tube walls not only reduces the incidence of fouling with a resulting beneficial effect on equipment life , but it also has the desirable effect of promoting heat transfer from the tube wall to the liquid in the tubes . Using a coating on the inner wall surfaces of the exchanger tubes may further reduce fouling and corrosion .

Steel Welding Fittings . Conclusion

% Elongation – 40 Hardness -205 BHN

The high nickel content of austenite 310 grade is superior to grades 304 , 316 , 321 and 309 . It combines high corrosion resistance and high-temperature properties with good ductility and fabrication characteristics . Due to the chemical composition of this grade , with chromium up to 25 % and nickel up to 20 %,

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

products manufactured in grade 310 provide solid corrosion resistance , excellent resistance to oxidation , and superior strength at high temperatures up to 1150 ° C . High nickel ( 25 +%) alloys are most commonly used to construct process equipment , including heat exchangers , when superior corrosion resistance and high-temperature mechanical properties are required .

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