Chrome-moly steel

M. Prager, Hydrogen Attack Susceptibility Of Chrome-Moly Steels And Weldments, PVP Vol. 239/MPC Vol. 33, Serviceability of Petroleum, Process, and Power Equipment, American Society of Mechanical Engineers, New York, 1992. 

Chrome-moly steels have % to 9% chromium and either % or 1% molybdenum. Chromium increases scaling resistance and molybdenum improves or provides elevated temperature strength. Carbon content is kept low to maintain weldability. Chrome-moly steels are widely used for piping and pressure vessels operating up to 1000°F in environments such as steam or hydrogen and are available in many product forms. The two most popular alloys are 1 chrome- moly and 2 chrome-1 moly. 

Many metals look alike. It is relatively easy to substitute the wrong metal when the identification has been obliterated or the accompanying paperwork lost. For example, chrome-moly steels look like carbon steel, are magnetic, and rust like carbon steel if stored outdoors. Chrome-moly steels are used in critical applications such as piping for handling steam or hydrogen. Carbon steel should not be mistakenly substituted for chrome-moly steel in a critical application, because it might fail catastrophically. 

In an effort to solve the problem of carbon fonna-tion without resorting to the use of high cost stainless steels, a sample of chrome-moly steel ws subjected to the alonizing process (aluminum impregnation). Table VII demonstrates the successful pacification of the surface ... 

Shafts are made of material ranging from medium carbon to low alloy steel and are usually heat treated. Shafts were originally made of forgings for the compressors in process service. But because of the availability ot high quality material, hot rolled bar stock has been used for shafts up to S inches in diameter. Bar stock shafts are given the same heat treatment and quality control as forgings. Many of the process users prefer a low alloy, chrome-moly-nickel material for shafting, particularly for compressors in critical service. 

OD Tube Gauge Factor Carbon Steel Admiralty Red Brass,. 45% Ars. Copper 4-6% Chrome V2 % Moly Steel 80-20 CU-NI 70-30 CU-NI Monel Copper 99.9+ % CU Nickel Aluminum Stainless AISI Type 302 304 Yorkalbro, Aliun. Brass... 

Tempering Heating a quench hardened or normalized ferrous alloy to a temperature below tbe transformation range to produce desired changes in properties, predominantly to soften or toughen. It is used to remove brittleness from quench hardened steel. In chrome moly Q T steel, the tempering processs is accomplished by the final PWHT. 

These deposits were formed by exposing the mild and the chrome-moly carbon steels to a flow of 2-methyl-2-pentene at a residence time of two seconds and a temperature of 550°C for tMo hours. A shortened activation period was achieved by exposing the steels to the hydrocarbon stream at 70C°C for 1/2 hour at a residence time of 2 seconds. To test this deposit for heterogeneous activity, the earlier reaction conditions (2.0 seconds residence time at 550° ) were used. 

My experience indicates that stainless steels that have high chrome and nickel content are not very resistant to naphthenic acid attack. What is required is molybdenum. 304 stainless steel is unsuitable due to its low moly content. Even 316 stainless steel, which has about 2 percent moly, offers only marginal protection. I usually specify 317 stainless steel, which has about 3 percent moly, when designing for naphthenic acid services. 

The 300 series stainless steels contain nickel (316 and 317 also moly). The 400 series chrome steels are intended mainly to resist sulfur and high temperature. The 300 series steels have a greater range of chemical resistance. A handheld instrument is now available to discriminate between carbon steel, chrome steel, and different types of stainless steels. 

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