Weldments carbon steels

NACE International Standard RP0472-95, Methods and Controls to Prevent In-Service Environmental Cracking of Carbon Steel Weldments in Corrosive Petroleum Refining Environments. 

Carbon steels. The corrosion behavior of carbon steel weldments produced by fusion welding can be due to metallurgical effects, such as preferential corrosion of the heat-affected zone (HAZ) or weld metal, or it can be associated with geometric aspects, such as stress concentration at the weld toe, or creation of crevices due to joint design. 

Additionally, specific environmental conditions can induce localized corrosion such as temperature, conductivity of the corrosive fluid, or thickness of the liquid corrosive film in contact with the metal. In some cases, both metallurgical and geometric factors will influence behavior, such as in stress-corrosion cracking. Preferential weldment corrosion of carbon steels has been investigated since the 1950s, commencing with the problems on icebreakers, but the problem continues today in different applications. (Bond)5... 

The CE value is used to evaluate the risk of developing hard HAZs and the susceptibility of the weldment to delayed hydrogen cracking. Table 21.1 shows typical limits for carbon steels. When the maximum allowed CE value is exceeded, additional fabrication measures such as preheat, PWHT, and/or inspection for the effects of delayed hydrogen cracking are usually necessary. 

Schweitzer, Philip A., ed. 1996. Corrosion Engineering Handbook. New York Marcel Dekker. Caplan, F. 1975. Is Your Water Scaling or Corrosive Chemical Engineering September 1 29. NACE International. Current edition. Methods and Controls to Prevent In-Service Environmental Cracking of Carbon Steel Weldments in Corrosive Petroleum Refinery Environments. NACE RP0472. Houston, TX NACE International. 

It is absolutely imperative that all corrosion inhibitor evaluations be made on metal specimens encountered in the field. It had been pointed out above that [27,25] the effective inhibitor concentration on two different oilfield steels (J-55 and L-80) was vastly different under severe conditions. Examples of this abound in the industry. Weldments of carbon steel piping containing a small amount of copper were more difficult to inhibit under relatively mild conditions. 

SSC of carbon steel weldments in hydrogen sulfide service is controlled by the following procedures described in NACE Standard Methods and Controls to Prevent In-Service Cracking of Carbon Steel (P-1) Welds in Corrosive Petroleum Refining Environments (RP0472). This includes... 

NACE International. 2005. Methods and controls to prevent in-service environmental cracking of carbon steel weldments in corrosive petroleum refining environments, NACE Standard RP0472-2005, Houston NACE International. 

The corrosion behavior of carbon steel weldments is dependent on a number of factors. Consideration must be given to the compositional effects of the base metal and welding consumable and to the different welding processes used. Because carbon steels undergo metallurgical transformations across the weld and HAZ, micro-slructures and morphologies become important. 

Before 1978, postweld stress relief of carbon steel weldments in MEA systems was performed only when the metal temperature of the equipment was expected to exceed 65 °C (150 °F) and the acid gas contained more than 80% COj, or when temperatures were expected to exceed 95 °C (200 °E) in any acid gas concentration. 

Leaking Carbon Steel Weldments in a Sulfur Recovery Unit... 

Under certain conditions it is possible for a weldment to suffer corrosive attack which has the form of a fusion line crack emanating from the toe of the weld this is termed knifeline attack. It is occasionally experienced in welded stabilised steels after exposure to hot strong nitric acids. The niobium-stabilised steels are more resistant than the titanium-stabilised types by virtue of the higher solution temperature of NbC, but the risk may be minimised by limiting the carbon content of a steel to 0-06 Vo maximum (ELC steel). 

P.P. Puzak, "Explosion-Bulge-Test Performance of Low-Carbon Ni-Cr-Mo-B Quenched and Tempered Steel Weldments ,... 

Fe-H-C-i Austenite/Austenite Type Weldments , Met Mater, 37(2), 61-67 (1999), translated from Kovove Mater. 37(2), 85-95 (1999) (Transport Phenomena, Theory, 10) [1999Sta] Stavinskaya, O.N., Shklovskaya, N.I., Some Features of Activation of Synthetic Carbons by Iron-Catalyzed Hydrogenation , Russ. J. Appl. Chem., 72(5), 783-787 (1999), translated from Zh. Prikl. Khim., 72(5), 751-755 (1999) (Experimental, Catalysis, Phys. Prop., 13) [2000Pil] Pilous, V., Foret, R., Stransky, K., Redistribution of Hydrogen in Steel Weldments Part II. Fe-... 

Electrodes are made to match various types of stainless steels so that corrosion-resistance properties are not destroyed in welding. The most commonly used types of stainless steels for welded structures are the 304, 308, 309, and 310 groups. Group 304 stainless, with a maximum carbon content of 0.8%, is commonly specified for weldments. 

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