When design the pillow plates,how to choose the right materials to meet the requirements of corrosion resistance and strength?

When choosing materials to meet the corrosion resistance and strength requirements of Pillow plate heat exchangers, you need to consider several important factors. Let's make decisions based on the characteristics of these commonly chosen materials.

Assessing the Corrosiveness of the Medium

Mild Corrosion Environment: If the corrosiveness of the medium is weak, like ordinary fresh water or clean air, 304 stainless steel usually can meet the needs. It contains about 18% chromium and 8% nickel. It can form a passive film to resist mild corrosion. It costs relatively less and is easy to process. It is widely used in common heat - exchange scenarios in HVAC systems.

Medium - Corrosion Environment: When the medium is somewhat corrosive, especially when it contains chloride ions, 316L stainless steel is a better choice. It adds 2 - 3% molybdenum based on 304, which enhances its resistance to pitting and crevice corrosion caused by chloride ions. It is often used in industries such as chemical engineering and food processing, where the heat - exchange process involves fluids with a small amount of corrosive media.

Strong Corrosion Environment: In strong - corrosive media such as chemical solutions like sulfuric acid and phosphoric acid, or in environments with high - concentration chloride ions, 904L stainless steel, 2205 duplex stainless steel, 2507 super - duplex stainless steel, and titanium materials are more suitable. 904L contains a high proportion of chromium, nickel, molybdenum, and copper, and has excellent resistance to many strong - corrosive media. 2205 and 2507 duplex stainless steels have both strength and corrosion resistance due to their austenite - ferrite duplex structure, and they have excellent corrosion resistance to chloride ions. Titanium materials perform extremely well in strong - corrosive environments such as oxidizing acids and seawater, and can form a very stable passive film.

Analyzing the Strength Requirements

Low - Pressure Conditions: For heat exchangers with low operating pressure, the strength of 304 and 316L stainless steels is sufficient. Their mechanical properties can ensure the stability and safety of the heat - exchanger structure under normal pressure.

Medium - and High - Pressure Conditions: When the operating pressure is high, 2205 and 2507 duplex stainless steels have obvious advantages. The duplex structure gives them higher strength than austenitic stainless steels. The yield strength of 2205 is about twice that of 304 and 316L, and 2507 has even higher strength. They can withstand greater pressure and are suitable for heat - exchange equipment in high - pressure environments such as petrochemical engineering and offshore platforms.

Considering the Temperature Factor

Low - Temperature Environment: Most stainless steels can still maintain good mechanical properties at low temperatures. However, titanium materials not only do not reduce their strength at low temperatures but also have good toughness. They are suitable for low - temperature heat - exchange scenarios such as low - temperature refrigeration and liquefied gas heat - exchange.

High - Temperature Environment: 316L stainless steel can operate stably at a certain high temperature and can withstand a certain degree of thermal stress. 904L stainless steel also has good high - temperature performance and performs well in high - temperature and strong - corrosive chemical process heat - exchange. For higher temperatures and more severe conditions, special high - temperature - resistant alloys or further evaluation of the high - temperature stability of materials are required.

Balancing Cost - Effectiveness

Cost - Sensitive Projects: In projects with strict cost control and low requirements for corrosion resistance and strength, 304 stainless steel is an affordable choice. It is widely used in civilian and commercial heat - exchange equipment that is sensitive to costs.

Performance - Priority Projects: When performance is the primary consideration and cost is relatively less important, such as in high - end chemical engineering and deep - sea engineering, although 904L stainless steel, 2205 and 2507 duplex stainless steels, and titanium materials are expensive, they can ensure the long - term stable operation of the equipment and reduce maintenance and replacement costs. From the perspective of the whole life cycle, they have high cost - performance.

Evaluating the Difficulty of Processing and Maintenance

Processing Difficulty: 304 and 316L stainless steels are easy to process. They can be welded and formed easily and can be manufactured using conventional processing techniques and equipment. 2205 and 2507 duplex stainless steels are a bit more difficult to process. When welding, process parameters need to be controlled to ensure the stability of the duplex structure. 904L stainless steel and titanium materials are even more difficult to process. Titanium materials need to be welded under the protection of inert gas, and the processing cost is high.

Maintenance Difficulty: Different materials have different maintenance requirements. In a medium environment where scaling is likely to occur, materials with a smooth surface and good corrosion resistance are easier to clean and maintain. For example, titanium materials are not easy to scale on the surface, and during maintenance, their excellent corrosion resistance reduces the risk of corrosion caused by improper maintenance.