Cryogenic treatment of metals significantly reduces wear and corrosion in marine components, resulting in reduced maintenance, reduced replacement costs, and extended service life. However, this technology has been slow to develop since World War II and has only recently become an effective means of improving the wear and corrosion resistance of heat-treated components.
This article will explore the advantages of cryogenic treatment, the reasons for its slow development, and how it will be used in oil and gas (O&G) and marine applications.
Problem
Increasing the tensile and yield strength of carbon steel wire and fasteners without increasing hardness is a persistent challenge for heat treaters serving the offshore, wind energy, and oil and gas industries.
Subsea bolts, risers, and umbilicals used in Christmas trees, wellheads, offshore platforms, and moorings are constantly subject to corrosion and abrasion from seawater. While these components often fail due to excessive assembly torque or manufacturing defects, the root cause is often insufficient mechanical strength and stress corrosion cracking (caused by hydrogen embrittlement).
A common method for increasing the ultimate tensile strength of carbon steel wire and fasteners is to increase their hardness through austenitization and quenching. This is because higher hardness favors carbon steel at high temperatures, where ductile fracture typically occurs.
However, carbon steel used in low-temperature marine environments experiences brittle fracture. Therefore, increasing hardness has the opposite effect on extending the service life of deepwater materials.
Specialty alloy alternatives can help, but are limited by high prices and availability. Carbon steel is inexpensive and widely available, but it often contains hydrogen. The diffusion of hydrogen along grain boundaries prevents carbon steel from meeting the service life or performance requirements in seawater environments.
Cryogenic Treatment Solutions
Cryogenic treatment (DCT) is a low-temperature process that can reduce corrosion, wear, fracture, and fatigue issues in most metal components by 20–70%. Prolonged exposure to temperatures as low as -310°F (approximately -190°C) in dry nitrogen vapor (Figure 1) improves mechanical properties.
Figure 1. Examples of cryogenic treatment processes. Each material requires different treatment steps.
The metallurgical changes that occur during treatment are the transformation of retained austenite to martensite (for ferrous materials) and the irreversible precipitation of primary and secondary carbides.
While many methods have been used to investigate this, such as scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction, and nanostructured characterization, the mechanisms of improvement resulting from cryogenic treatment remain unclear.
Standard ASTM destructive and nondestructive testing indicates that cryogenic treatment can:
- Increase the tensile and yield strength of carbon and bearing steels by 10–20% (Figure 2)
- Reduce corrosion in high-carbon steels by 20–60% (Figures 3 and 4)
- Reduce wear in some low- and high-carbon steels by at least 30% (Figures 5 and 6)
| Material and Treatment Condition | Yield Strength (ksi) | Ultimate Strength (ksi) | Strain (%) | Stress (%) | Reduction in Fracture Elongation (%) |
| 52100, not cryo-treated, standard | 268 | 359 | 2.5 | 3.9 | 6 |
| 52100, cryo-treated + tempered | 317 | 382 | 1.6 | 3.5 | 1 |
| 52100, tempered + cryo-treated | 320 | 376 | 1.8 | 3.8 | 4.5 |
| 4340, not cryo-treated, standard | 221 | 295 | 15.3 | 12.5 | 51.7 |
| 4340, cryo-treated + tempered | 240 | 300 | 14.2 | 11.6 | 51.3 |
| 4340, tempered + cryo-treated | 221 | 287 | 15.9 | 12.3 | 51.6 |
Figure 2. Cryogenic treatment of 52100 and 4340 steels shows a 20% increase in yield strength of the cryogenically treated steel.
Figure 3. Potentiodynamic pitting corrosion resistance test of 4340 steel (3.5% sodium chloride solution, 36 hours): (a) three cryogenically cooled samples, (b) three non-cryogenically cooled samples.
Figure 4. Uniform surface corrosion test of 4340 steel. After 18 hours of testing in 3.5% sodium chloride solution, the corrosion level of the cryogenically treated sample (a) was reduced by 64% (volume ratio) compared to the non-cryogenically treated sample (b).
Figure 5. Comparison of wear depth from pin-on-disc wear tests. The results of the 30-minute test show an 84% reduction in wear depth.
Figure 6. High-load ball-on-disc friction testing of 1018 steel shows a 30% reduction in average wear rate (a) for cryogenically treated and non-cryogenically treated material. A similar trend is observed for average wear depth (b).
Industrial applications for cryogenic treatment include oil and gas, marine, turbines, nearly all additively manufactured (i.e., 3D-printed) components, automotive, electric vehicles, wind and tidal power, and more. Cryogenic treatment effectively alleviates one of the biggest challenges facing all manufactured products: extending their service life.
How it works
Parts are slowly cooled from ambient temperature to -310°F (-190°C) in a specially designed chamber, held in a dry atmosphere for 18–60 hours, then slowly returned to room temperature and subjected to one to three annealing cycles (required to eliminate hydrogen embrittlement).
The entire process takes three to four days and doubles the wear and corrosion life at approximately 5% of the original part cost. The process can be performed in batches and can process parts weighing thousands of pounds. The cryogenic treatment process is non-toxic, uses no chemicals, and produces no environmentally harmful waste.
Cryogenic treatment is effective for raw materials, castings, forgings, additively manufactured (i.e., 3D-printed) parts, and machined components. It operates on the entire through-hole component, unlike surface treatments or coatings even if the coating corrodes, the component remains wear-resistant.
This process is typically (but not exclusively) performed after heat treatment to improve the properties of steel, aluminum, copper, titanium, refractory alloys, and metal matrix composites. It is more effective for single-phase steels than for duplex steels.
Cryogenic treatment is characterized by its rapidity, effectiveness, low cost, and environmental friendliness. It is strongly supported by over 25 years of quantitative scientific research conducted by world-class universities. The process has reached a Technology Readiness Level (TRL) of 3-5, making it suitable for large-scale industrial applications.
Development history and process equipment
Cryogenic treatment gained significant momentum during World War II, when attempts were made to extend the wear life of forging dies for aircraft components by pouring liquid nitrogen over them. However, this often resulted in fatigue cracking and fracture of the dies due to thermal shock.
Between 1980 and 2000, technological advances such as digitally controlled liquid nitrogen supply, the use of dry nitrogen vapor, PID optimization, and in-situ annealing significantly improved cryogenic treatment performance.
However, most processes utilize small chambers—the largest industrial system measures only 0.91 m x 0.91 m x 1.82 m. This small size is a major obstacle to industrial adoption. Barriers to Adoption
Until recently, the adoption of cryogenic treatment has been hampered by the following factors:
- No widely known testing or verification methods
- No cryogenic treatment certification or acceptance criteria based on practical experience
- No large-scale cryogenic chambers are capable of processing the size or quantity of industrial components required
- No large-scale chamber or service providers
There are approximately 130 in-house or independent cryogenic treatment providers worldwide, but few offer on-site testing, component certification, or documentation, or actual measurement of wear/corrosion performance improvements.
Unlike heat treatment, which is performed according to hundreds of ASTM, Nadcap, AMS, and MIL-STD standards, cryogenic treatment has no such standards. Customers can only take the cryogenic treatment provider’s word and use their payment receipt as proof of the cryogenic treatment, without formal industrial testing, verification, or acceptance.
Imagine the situation if a component in an airplane, automobile, or power generation equipment is not manufactured to standard or has never undergone process testing!
As a result, almost all end users are individuals working with small quantities of components, rather than military or industrial companies capable of large-scale R&D or process commercialization.
Scale-up equipment has only become available in recent years, and these large process chambers almost certainly require on-site liquid nitrogen production and equipment capable of off-site testing. These factors significantly hinder the adoption of this technology.
Certification
Both certification bodies, DNV-GL and Lloyd’,s have proposed proposals for future applications of this technology in the oil and gas industry. Because cryogenic treatment does not change the supply source, material type, manufacturing method, dimensional tolerances, or even the end use, certification time can be shortened even for the traditionally conservative energy industry.
A key advantage of cryogenic treatment is that it can be directly added to existing production processes without changing or eliminating any prior steps.
A recently approved patent by the US Patent and Trademark Office may further improve certification methods. It proposes destructive and nondestructive testing of artificial coupons placed in each batch of cryogenically treated parts. Existing ASTM friction and corrosion methods are used for coupon testing, relying on high-quality optical profilometers and tribometers to generate reliable and parametric certification data. Further Applications of Cryogenic Treatment
Many marine components, such as power generation equipment, transmissions, subsea risers, umbilicals, drill strings, and drill pipe, are well-suited for cryogenic treatment to improve their performance.
However, cryogenic treatment of wear-prone components, including drill bits, valves and corrosion-resistant sleeves, thrust bearings, nozzles, and gears, offers a better entry point, enabling the use of low-cost carbon steels instead of expensive superalloys and carbides.
For mines, cryogenic treatment of crusher rollers, mill liners, pump nozzles, and slurry pipe components that often fail due to abrasion, rolling contact fatigue, mechanical fatigue, or high-stress impact wear is expected to significantly increase equipment uptime and reduce maintenance.
Conclusion
Cryogenic treatment will enable heat treaters and end users to significantly reduce wear and corrosion in marine and industrial components. The technology is now mature, with the introduction of empirically based acceptance criteria, destructive and non-destructive testing methods, large-scale treatment chambers, and certification schemes. Those who are the first to invest in large-scale cryogenic chambers and implement testing/certification programs are likely to gain a first-mover advantage. This represents a significant change in metal heat treatment, enabling customers to reduce downtime, repairs, and replacement costs, thereby increasing their bottom line. Ultimately, it will be a breakthrough technology.
