Stainless Steel World Americas Journal December 2023 | Page 13

Table 3 — Mechanical Properties

Min . req VdTüv WB505

Min . req B 622

K33 ( N06059 )

Rp0.2 Min Rp1.0 Min Rm A 2 ” % Impact J / Cm2

340 380 690-900 40 225

310 na 690 45 na

444 ( Avg ) 478 ( Avg ) 836 Avg 62 229

Higher yield strength of Alloy 59 vs N10276 / N06022 allows for the use of a smaller wall thickness in seamless tubular applications allowing for the reduction in cost and weight .

leading to accelerated corrosion on the tube ’ s outside diameter ( OD ). Alloy 59 is an option in such environments as it has good resistance to chloride-induced pitting or stress corrosion . This is helpful on the tube ’ s inside diameter ( ID ) if it has cooling water containing a high percentage of chlorides . depends on the characteristics of the contaminants contained in the organic acids , and on operating temperatures . From tests , it was concluded that Alloy 59 is the best material for use in acetic and formic acid up to 300 º C .

Flue Gas Desulfurization

Graph 2 : G28 Method A ( Resistance to Intergranular Corrosion ); Ferric Sulphate and Sulphuric Acid Boiling Test – 50 % H2SO4 + 42g / liter FE2 ( SO4 ). 3

Geothermal Power Plants

Gas unit sulfur condensers are often subjected to severe corrosion due to sulfuric acid dew point corrosion . In some cases , carbon steel has a life of less than one year . Alloy 59 is a suitable alternative in such harsh environments . Alloy 59 can also be used in narrow temperature and concentration ranges for handling HF acid in Alkyl units with an HF catalyst . For bio / green diesel plants , hydrotreating Alloy 59 can be used for resistance to corrosion against fatty and carbonic acids .

Petrochemicals — Acetic Acid / Formic Acid / Sulfonic Acid

Condensers and other components are prone to heavy corrosion when acids are contaminated by oxidizing chlorides . Formic acid reduces but can shift to oxidizing in the presence of contaminants . The use of nickel-containing stainless steels like Alloy 59 can help to mitigate corrosion in such process conditions , while corrosion severity depends on the method of acetic acid production . Anhydrous acetic acid can increase the corrosion rate . Hot acetic acid and the presence of chlorides can also increase corrosion rates .

Alloy 59 works well in both oxidizing and reducing conditions , making it an ideal candidate for tubes , pipes , and more . The performance of the various alloys largely

Table 4

There are different absorbents used to remove sulfur from exhaust emissions . In most cases , there is a possibility of the formation of sulfuric acid as a byproduct under high temperatures which causes severe corrosion . Alloy 59 works best in these conditions when compared to C alloys . It is the purest form of Cr-Ni-Mo with minimal Fe and therefore gives the best results .

Ammonium Sulphate

Ammonium sulphate can be one of the absorbents to remove sulfur in FGD . Saturated ammonium sulphate solution with 10,000 ppm of chloride and pH of 1 at 93˚ C was stimulated by syncrude . Alloy 59 gave the best results . This construction often gives a life of 20 plus years .

Fluoro Chloro Compounds

Manufacturing of Fluoro Chloro compounds involves Hydrochloric acid ( HCl )/ Hydrofluoro acid ( HF )/ dichloro methane as by-products . Fluorides and chlorides , which are part of the Halide group , cause severe pitting corrosion , which accelerates further with concentration and temperature . The materials used in operating such conditions need high PREN and Alloy 59 can be used . This material has one of the highest PREN which works well in oxidizing and reducing conditions .

Graph 3 : CPT in Green Death Solution ( 8vol .% H 2

SO 4

+ 3vol .% HCI + 1 % CuCl 2 + 1 % FeCl 3 x 6

H 2

O after repeatedly heating for 24 hours using 5 ° C ( 9 ° F ) temperature increments ).

Geothermal fluids containing dissolved

CO 2

, H 2 S , NH 3

, and chloride ions , can cause corrosion of metallic materials . Therefore , the safe utilization of geothermal systems depends on material selection . Corrosion types encountered in geothermal systems include : uniform corrosion , pitting corrosion , sulfide stress corrosion cracking ( SSC ), hydrogen embrittlement , and erosion corrosion .

For high temperature geothermal fluids , it is suitable to use Ni-Cr-Mo alloys as a material . Alloy 59 , having very similar Mo content to UNS N06022 , has also shown outstanding pitting corrosion resistance in highly saline geothermal environments of near-neutral pH at 150˚ C . By having high amounts of Molybdenum in the alloy , the influence of temperature on pit nucleation and repassivation can be significantly reduced .

Welding

Low carbon and silicon content mean good weldability without susceptibility to hot cracking . Weld consumables in Alloy 59 have extra low carbon . High nickel filler metal with Chromium and Molybdenum can be used for MIG , TIG , or plasma arc welding to itself or other nickel-based alloys . Alloy 59 weld overlay has proven to be effective in other Cr-Ni-Mo alloys , Alloy 625 , and even super austenitic alloys such as 6 Moly . This holds a low sensitivity to hot cracking . Alloy 59 has the lowest corrosion rates in weld zones tested with high chlorides and low pH , compared to N10276 / N06022 .

About the Authors

Heat exchanger assembly .

Sample tubes for testing .

In Conclusion

Alloy 59 is quite versatile material as it can be used in oxidizing and reducing conditions . One of the purest Cr-Ni-Mo alloys has a minimum of unwanted alloying elements which makes it have excellent corrosion resistance . Alloy 59 also has good weldability features and can be used as an option to other Cr-Ni / Mo , C-Grades . It is also available in other forms such as plates / scheduled pipes , large OD pipes , fittings , flanges , and more .

M Venkat Ramesh , Global Product Manager , Heat Exchanger tubes , Tubacex , has worked more than 17 years in stainless seamless tube and pipe industry in different roles including Sales , Business development , Key Account , Technical marketing and as Product Manager . He has worked closely with some of the refineries and chemical companies involving suggestions and resolving corrosion issues , material testing , material upgrade suggestions etc . He has published technical articles in Leading Industrial Magazines and presented a paper at NACE in the past .

Shabareesh Nair , Technical Marketing Director-Asia , Tubacex , has a Bachelor ’ s in Mechanical Engineering , and a Post Graduate Diploma in Marketing Management . Having a total industry exposure of 15 years , the last 12 years have been exclusively with the Stainless Steel industry and has been associated with a similar industry before joining Tubacex . At Tubacex , responsibilities include developing hydrogen value proposition in Asia , Technical Marketing support to the regional offices in Asia and identifying and developing new business applications / opportunities .

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