15MnVR steel welding pipe technology in hydropower penstock

Keywords: steel pipe material welding technology

1 , materials

1.1 , 15MnVR steel (base material)

The 1.1.1 , 15MnVR steel characteristics

15MnVR steel is normalized condition steel. (Normalized steel is on the basis of the solid-solution strengthening, precipitation strengthening and grain refinement to further improve the strength and to ensure the toughness of a Class of High Strength Low Alloy Steel)

15MnVR steel chemical composition table:

15MnVR steel mechanical properties table:

Note: d = diameter of the bending center of   a = thickness of the sample

This type of steel is to achieve grain refinement and precipitation strengthening 16Mn based on adding a small amount of V ( 0.04% - 0.12% ). This steel normalizing state, but because of the form of vanadium carbide distribution and the degree of dispersion strengthened hot rolling temperature, cooling rate have a great relationship. Therefore its performance fluctuations can be larger in the hot rolling state, the plate thickness increases even more serious. Due to this the steel substance should belong to the type of precipitation strengthening steel, it is only through normalizing the grain and carbonized steel uniform dispersion precipitated, in order to obtain higher ductility and toughness of this steel in the signing of the contract requirements normalizing the state under delivery, non-destructive inspection and grade Ⅱ Delivery. The purpose of normalizing To make these alloying elements to the fine quality of the compound is precipitated from the solid solution, and also from the grain refinement effect is suitably improved while improving the strength, the ductility and toughness of the steel, in order to achieve the strongest overall performance.

The 1.1.2 , 15MnVR steel welding analysis

By the steel features can be seen 15MnVR better steel welding.

The knot mainly through technological factors described weldability 15MnVR .(Affect weldability material factors, technological factors, structural factors and use factors.) 15MnVR steel weldability usually appear two issues: First welding caused by a variety of metallurgical defects, mainly various types of cracks; two welding variation of the performance of the material.

1.1.2.1 , prevention of weld hot cracking

Lower carbon content of this steel from the the normalized steel components, with a higher amount of Mn , Mn / S ( S- containing element multi-cause thermal cracking) than to meet the requirements, better thermal cracking performance, under normal circumstances does not appear in the next weld hot cracking. But when the material composition failed, or the local C due to severe segregation , the S high levels prone to hot cracking. In this case, the welding material on the use of a wirecontaining Mn, and containing SiO 2, the lower flux, thereby reducing the amount of the carbon in the weld, and improve the manganese content in the weld, resolves the hot crack problems. In the engineering Ajiutian wire H 10 Mn 2 flux HJ431 .

1.1.2.2 prevention weld cold cracking

The cold crack is a major problem in the the welding 15MnVR steel. Consider the hardened tissue ( a ) from the material itself is the cause cold cracking decisive factor, due to the higher level of normalizing the strength of steel, the more content of alloying elements. Therefore, compared with low carbon steel, weldability difference. ( b ) carbon equivalent and cold cracking tendency. Analysis from the front of the material hardened tendency to affect the cold cracking tendency hardened tendency depends mainly on the chemical composition of the steel, the most obvious of which the role of the carbon. Therefore, it can roughly be estimated and this different steels cold cracking tendency, in order to reduce the amount of containing C, to improve 15MnVR welding some of the alloying elements V , but must be added in order to make up for the loss of strength through some empirical carbon equivalent formula . Carbon equivalent can not accurately determine the cold cracking or not, because the cold cracking in addition to the ingredients and other factors. In order to avoid cold cracking, you need to take a more stringent process measures, in the strict control engineering Ajiutian line energy, preheat and post-weld heat preservation measures.

1.1.2.3 reheat cracking

15MnVR steel, is not sensitive to reheat cracking.

1.1.2.4 lamellar tearing

To produce lamellar tearing is not the type of steel and the intensity level restrictions, tear and the thickness. As Ajiutian power plant using the thinnest15MnVR steel thickness δ = 28mm , prone to lamellar tearing. Steel plate itself, mainly depends on the smelting conditions, the steel factory must be non-destructive inspection, Ⅱ grade the flaw qualified granted factory. General in engineeringconstruction Ajiutian process of thickness more than 32mm , take 150 º C preheated no lamellar tearing phenomenon in the entire construction process.

The 1.1.3 , 15MnVR Steel acceptance

15MnVR steel GB/T1591-1994 , GB6654 - 1996 provisions, and has a factory certificate of compliance and quality assurance. 15MnVR steel use before inspection and acceptance of GB6654-1996 container board. Transport and storage of steel plate deformation, corrosion, damage and should be avoided.

1.2 , 15MnVR Steel welded materials

1.2.1 , the welding material is to determine the main factors of the welding quality.Welding materials selection based on 15MnVR mechanical properties, chemical composition, joints steel and steel pipe beveling and use requirements selected. In the selection of manual arc welding in Ajiutian engineering E5015 electrode, wire select H 10 Mn 2 the flux election HJ431 . Select the above welding material must have factory certificate of compliance and quality assurance.

1.2.2 , the storage and safekeeping of the Welded pipe, wire and flux should JB3223-83"welding rod" of quality management procedures implemented.

1.2.3 , prior to the use of electrodes and flux in strict accordance with the provisions of the manual drying; wire stored in a dry place to prevent damp rust.Welding rod, wire and flux of the person responsible for the custody, drying and payment, and detailed records.

1.2.4 , the dried electrode and flux save in the 100 - 150 º C thermostat box, with the-box; each welder equipped with insulation tube, insulation tube in the process of using ohmic heating, welding rod taken with a root. The insulation barrel more than 4helectrode drying should be re-drying, the drying number should not be more than twice.

1.2.5 , the flux is provided by the manufacturer of the use requires. Flux after drying, the removed solder placed in a sealed container and taken to use in the field, the flux in the air after drying 4h above re-drying, the drying does not exceed the number of three times. Molten solder is no longer used, the flux, use rice sieve screening, strictly prevent oxide debris mixed, and after re-drying can be used again.To prevent waste, the flux can be used repeatedly, but continually adding new flux drying, and blended uniformly.

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