Weld Repair of 310S Stainless Steel Pipe Crack

• 2022-01-17
 
• Posted by Wilson

310S is a heat-resistant stainless steel, with good oxidation resistance, corrosion resistance, widely used in ion-exchange membrane electrolysis of the alkaline pipeline. As the material process requirements are high, once the base metal and filler material alloying elements are not complete, improper welding process, working condition is not good, pipe corrosion, work stress and other reasons will cause serious defects in pipeline cracks, will bring to the production A serious risk. So, the welding of the crack repair has become an important maintenance method.

First, the crack for direct welding (mainly used for ≤ φ89 pipe cracks)
1, do the preparatory work before welding, from the two ends of the crack at the end of each 10mm drill φ6mm crack hole, has prevented the grinding process of welding crack propagation. And then use the angle grinder grinding groove angle α = 60 °, gap b = 3.2mm, blunt edge p = 1.5mm groove. The length of the groove is the distance between the cut holes, and through the hole grinding out the weld and the base metal transition surface, and the groove on both sides of the oil, rust and other debris clean up.
2, the use of ZX7-400A welder, DC reverse, welding consumables A402, φ3.2mm for rendering, filling and cover, welding current of 110A.
3, the use of arc welding primer, even with arc welding and cover, and single-channel primer, double-channel filling, 3-channel cover. Everything is thoroughly cleaned, each connector should be staggered around 15mm, to ensure that no defects. Welding direction from left to right, the order of welding for the layer by layer from bottom to top.
4, after welding, the appearance of the weld to be flat and weld height h ≤ 1mm, width ≤ 4mm, done by color inspection qualified to use after normal use.

Second, dig repair repair (mainly used for ≥ φ89 pipe cracks)
Dumping repair is the pipe has been the site of the crack, with a plasma arc to completely cut off, and dig out the width of 150mm, than the two ends of the visible cracks at the end of 20mm pipe base material. And then according to the size of the excavated base material to choose the same axis with the material patch block, the repair site for welding repair.
1, grinding and group pairs In order to avoid stress concentration, so that welding seam smooth transition, you must first dig holes and patches of the edge of the cut off 1mm, and then the four corners polished into a circular arc, and finally repair the V-shaped Groove, and the groove on both sides of oil, rust and other impurities clean up. Recommended groove size: bevel angle α = 60 °, reserved gap b = 3.2-4.0mm, blunt edge p = 1.5-2.0mm. Welding to strictly control the gap size, and to be basically the same.
2, welding equipment and methods of welding machine using ZX7-400A or other inverter DC, silicon rectifier welder, are DC reverse, so that the welding process arc stability, splash small, so as to further ensure the quality of welding. Welding using argon arc welding base, to prevent the electrode arc welding electric residue in the pipeline caused by damage to the equipment. Using A402φ3.2mm electrode welding arc welding, cover. Welding current control in the 85-105A, and each arc after cooling 3-4S and then arc, the electrode swing the smaller the better.

  

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Low Temperature Performance of Stainless Steel Welded Pipe

• 2022-01-17
 
• Posted by Wilson

Low temperature performance of stainless steel welded pipe is shown below

1. Low temperature embrittlement 
In low temperature environment, the deformation energy is small. In low temperature environment, the elongation and the decrease of the shrinkage of the section are called low temperature embrittlement. And more in the ferrite series of body-centered cubic tissue.

2. Low temperature processing
Martensitic stainless steel is from the austenitizing temperature quenching and then cooled to very low temperature, in order to promote the martensite quenching method. Suitable for easy production of residual austenitic stainless steel.

Stainless steel welded tube at low temperatures, resistance, linear expansion coefficient, thermal conductivity, quality of hot melt and magnetic will change greatly. Resistance, the linear expansion coefficient decreases at low temperature; thermal conductivity, mass heat capacity decreases drastically at low temperatures; Young’s modulus (longitudinal modulus) increases at the same time as the temperature decreases. Since the austenitic stainless steel tube has a Ms point (martensitic starting temperature or martensite formation temperature) of a low temperature (Subzreo temperature), martensite can be generated when it is kept below the Ms point. At low temperature, the formation of martensite, so that the representative of the series of stainless steel steel SUS304 (18Cr-8Ni) at room temperature is non-magnetic, and in low temperature environment into a magnetic.

On the low temperature state, the ferrite stainless steel pipe exists like carbon steel as low temperature brittleness, while the austenitic steel is not present. So ferritic or martensitic stainless steel produces low temperature embrittlement and Austenitic stainless steel or nickel based alloys do not show low temperature brittleness. SUS410 (13Cr) and SUS430 (18Cr) of ferritic stainless steel tube show a sharp drop in impact value at low temperature. Therefore, when used in a low temperature, it is necessary to pay special attention. As a method for improving the impact toughness of ferrite series stainless steel, a high purification process can be considered.

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 NEWS

304 Stainless Steel Pipe Annealing Requirements

• 2022-01-17
 
• Posted by Wilson

The annealing requirements for 304 stainless steel pipe are as follows:
1, Whether the annealing temperature reaches the specified temperature. 304 stainless steel pipe heat treatment is generally taken to solve the heat treatment, which is commonly known as the “annealing”, the temperature range of 1040 ~ 1120 ℃ (Japanese standard). You can also observe the hole through the annealing furnace observation, the annealing area of the stainless steel pipe should be incandescent state, but did not appear softening sagging.

2, Annealing atmosphere. 304 stainless steel pipes are generally used as the annealing atmosphere of pure hydrogen, the atmosphere purity is best to more than 99.99%, if the atmosphere is another part of the inert gas, then the purity can be lower, but absolutely can not contain too much oxygen, water vapor. 

3, The furnace seal. 304 stainless steel pipe bright annealing furnace should be closed, and the outside air isolation; the use of hydrogen as a protective gas, and only one exhaust port is through (used to ignite the discharge of hydrogen). Check the method can be used soap water wiped in the various joints of the annealing furnace joints to see whether the run gas; one of the most easy to run the place where the furnace into the pipe and the place where the pipe, the place of the ring is particularly vulnerable to wear, Always check for regular changes. 

4, Protection of gas pressure. In order to prevent the emergence of micro-leakage of 304 stainless steel pipe, furnace gas should maintain a certain positive pressure, if it is hydrogen protection gas, the general requirements of more than 20kBar. 

5, The furnace water vapor. On the one hand to check the furnace material is dry, the first furnace, the furnace material must be dried; the second is into the furnace stainless steel pipe is too much residual water stains, special pipe above if there are holes, then do not leak into, Or else put the stove atmosphere all destroyed.

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Technical Requirements for Stainless Steel Tubes

• 2022-01-17
 
• Posted by Wilson

Technical requirements for stainless steel tubes are following below:

(1) Good corrosion resistance. The most basic requirements for stainless steel tube is corrosion resistance, that is, according to the use of different conditions, requiring steel pipe can withstand general corrosion, intergranular corrosion, point corrosion, stress corrosion. For the largest amount of austenitic stainless steel tube, resistance to intergranular corrosion is often the most basic requirements.
(2) Good processing performance differences. Stainless steel tube in the use of the process, most of the need for elbow, expansion and other processing, anti-corrosion steel pipe, so the steel pipe has a good flattening, flaring and other work performance.
(3) Good welding performance. Stainless steel tube for a large number of fluid pipeline, in use, anti-corrosion steel pipe welding is very large, the quality of each weld is very strict, responsible for causing a major accident.
(4) Good organization and performance stability, for long-term use at high temperatures endless steel pipe, due to the erosion of high-temperature media, oxidation, carburizing, the steel will change the organization, so the requirements of such steel should have Good organization and performance stability.
(5) Chemical composition evenly. Uneven chemical composition, will lead to uneven organization and performance of steel pipe in the entire pipe system or equipment to form a weak link or hidden danger, so the chemical composition is the most basic requirements.
(6) High dimensional accuracy. Steel pipe diameter and wall thickness of the accuracy, not only the construction and processing requirements, but also safe operation and reduce the cost requirements.
(7) Better surface quality. It is directly related to the use of performance, service life and cost reduction.

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How to Distinguish the Austenite and Ferrite Stainless Steel in Use

• 2022-01-17
 
• Posted by Wilson

Industrial use of stainless steel according to the metallographic organization can be pided into three categories: ferritic stainless steel, martensitic stainless steel, austenitic stainless steel. It can be the characteristics of these three types of stainless steel (as shown in the table below), but it should be noted that the martensitic stainless steel is not all can not be welded, but only by certain conditions, such as welding should be preheated after welding should be high temperature temper so that the welding process is more complex. The actual production of some martensitic stainless steel such as 1Cr13, 2Cr13 and 2Cr13 and 45 steel welding or more.

Ferritic stainless steel also belongs to chrome stainless steel
Low carbon content, anti-atmospheric, nitric acid and saline solution corrosion ability, high temperature oxidation resistance and so on. Mainly used in the production of chemical equipment in the container, pipe.

Austenitic stainless steel is chrome nickel stainless steel
Has a high corrosion resistance, excellent plasticity, good weldability and low temperature toughness, do not have magnetic, easy to work hardening. Mainly used in corrosive media work in parts, containers, pipes, medical equipment and anti-magnetic environment.

    

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he Production Environment of Stainless Steel Welded Pipe

 

The Production Environment of Stainless Steel Welded Pipe

• 2022-01-17
 
• Posted by Wilson

The production quality of stainless steel welded pipe is affected by many factors, including the environmental factors of the production site, stainless steel welded pipe manufacturers in the product quality control can not be ignored when the impact of this part. Here to talk about stainless steel welded pipe production environment control requirements:

1. Stainless steel welded pipe production need to have an independent production workshop or special fixed production site, stainless steel raw materials to ensure that a separate storage, can not be mixed with carbon steel.

2. Stainless steel welded pipe raw materials and semi-finished products in the process of turnover and transportation, should be equipped with the necessary anti-ferrous ion pollution and knock injury, scratched transport tooling.

3. Stainless steel welded pipe welding site is not allowed to wear a wind, to avoid the wind, rain, snow direct impact, the temperature is not less than -5 ℃.

4, stainless steel welded wire used in welding wire must have a dedicated welding material library to ensure that its storage temperature of not less than 18 ° C, humidity is not greater than 60%.

  

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Package of Steel Tube

• 2022-01-17
 
• Posted by Wilson

Package of steel tube requirements substantially pided into two categories: one is the common type of bale, and the other is with totes similar container load.

Bundled package
Avoid pipe damage by baling and transportation process, baling signs to a uniform and consistent.

The same bundle of steel pipe should be the same furnace number (Lot), with the steel grade, the same specifications of the steel pipe, should not be mixed furnace (batch) bundling, it should be less than a bundle into small bundles.

Weight of each pipe bundle should not exceed 50kg. The user’s consent to increase the bale weight, but the most important can not exceed 80kg.

Pipe bundle respect to the blunt end, should be aligned at one end, the tube ends are aligned side by less than 20mm, each bundle of steel pipe length difference less than 10mm, but according to the length of the pipe is usually the order of each bundle pipe length difference is less than 5mm, the longest pipe bundle and Minister of not more than 10mm.

Containers package
Cold-rolled or cold-drawn seamless steel tubes, the surface finish of hot-rolled stainless steel tube, the container may be used (such as plastic containers and wooden box) packaging.

Weight of the container shall be packed in accordance with Table 1. Negotiated by both sides, the maximum weight of each container can be increased.

When the pipe into the container, the inner wall of the container should be fitted cardboard, plastic sheeting or other moisture-proof material. Containers should not be closely seepage.

For steel containers and packaging, a label should be included in the container. The outer end surface of the container should also be linked to a label.

Steel with special packaging requirements, by agreement between.

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Difference between GI and MS

 Galvanized iron is iron which has been coated in a layer of zinc to help the metal resist corrosion. Steel can also be galvanized. When metal is going to be used in an environment where corrosion is likely, it is often galvanized so that it will be able to withstand the conditions. Even with galvanization, however, corrosion will eventually start to occur, especially if conditions are acidic.

There are two primary techniques which can be used to make galvanized iron. The most common is hot-dip galvanization, in which the iron is moved through an extremely hot bath of molten zinc, which may be mixed with small amounts of lead, depending on the circumstances. When the iron emerges from the bath, the zinc will have bonded, creating a layer of zinc on the surface of the iron. Sometimes, the metal may be passed through a mill to flatten and even out the coating. Another technique which can be used is electrodeposition, also known as electroplating, although this is rare.Once galvanized, iron is covered in a layer of zinc which may be shiny to dull gray. The zinc can be painted, if desired, or left plain. Painting is often done when the iron must match other building materials, or when people want to make it less obvious. In the garden, for example, it may be painted green so that it will blend in with foliage instead of standing out.

As long as the zinc coating remains intact, the galvanized iron should remain in relatively good condition. However, acidic conditions can erode the zinc over time, creating patches where corrosion can occur. Corrosion can also occur when the coating is penetrated, as when someone drives a nail through a sheet of galvanized iron, exposing the iron inside to the elements. Once corrosion starts, it can spread under the zinc, eventually causing the metal to fail.There are a wide range of uses for this type of iron, which comes in pipes, stakes, sheeting, and wire, among other formats. Many hardware and home supplies carry galvanized iron products and may be willing to cut pieces to custom sizes by request. People can also be referred to professionals who will weld or cut galvanized iron to meet the needs of a particular project.

Mild steel is the least expensive of all steel and the most common steel used. Used in nearly every type of product created from steel, it is weldable, very hard and, although it easily rusts, very durable. Containing a maximum of 0.29% carbon, this type of steel is able to be magnetized and used in almost any project that requires a vast amount of metal.Its structural strength prevents it from being used to create load-bearing girders and structural beams.Many of the everyday objects that are created of steel are made using mild steel, including automobile chassis, motorcycle frames, and most cookware. Due to its poor corrosion-resistance, it must be painted or otherwise protected and sealed in order to prevent rust from damaging it. A light coat of oil or grease is able to seal this steel and aid in rust control.

Unlike high-carbon steel, mild steel is easily welded. The properties of the steel allow the electrical current to travel through the metal without distorting the makeup of the material. Some types of high-carbon steel, such as stainless steel, require special techniques in order to properly weld the material. Being less brittle than high-carbon steels, the mild variant is able to flex and give in construction projects where a higher-carbon version could simply break.

Most of the pipeline in the world is created using mild steel. This allows the pipe to not only be easily welded into place, but also lets the pipeline flex and avoid cracking and breaking under pressure. The corrosive properties of the steel pipeline mean that it must be properly sealed through painting or a process often used on pipelines that involves wrapping the pipe with a corrosive-resistant material.Often in very cold climates, a warming type of insulating material is wrapped around the pipeline. This material helps keep the cold inside the pipe running smoothly. The wrap also prevents the soft mild pipe steel from becoming brittle and cracking. The constant expansion and shrinkage due to cold and warmth cycling in the pipe could create structural integrity problems, but these are held in check by the insulating wrap. On a much smaller scale, household pipes can be prevented from becoming cold and breaking by the use of electrical heating tape.

Finished products:

Mild steel pipe( seamless steel pipe, welded steel pipe)

GI pipe(galvanized steel pipe)

    

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304 Stainless Steel Seamless Pipe processing Fracture Analysis

 304 stainless steel seamless pipe blanks by quality, observed macroscopic fracture morphology analysis of the heating system and hot tube perforation occurred in pickling and cold working process, the analysis of the 304 stainless steel seamless pipe processing fracture causes. Noted rational selection process and adherence to the rules will reduce steel processing fracture. It made a number of concrete measures to prevent the occurrence of processing 304 stainless steel seamless pipe breakage.

Pickling) machining quality and yield, so hot piercing is one of the most critical step 304 stainless steel seamless pipe processing. The main factors affecting the quality of the thermal perforation are: billet heating system, perforated front billet temperature punch roll speed and penetration rates, capillary size and specifications …. stainless steel, etc., especially when the heating temperature and billet piercing machine when the roll speed selection unreasonable, in addition to easy to form a seamless 304 stainless steel inner and outer surfaces fold of skin, often cause capillary form a layered or implode. Layered shortage tube formation is often associated with high temperature or a hot piercing punch related to the roll speed too fast, capillary stratification during reaming it will crack, can be clearly observed from the fracture to the layered morphology. Layered steel caused by the above reasons, when the processing of stainless steel tube into a mechanical elbow find internal cracks.

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Galvanized Features

 The appearance of a bluish-white zinc coating, the standard electrode potential is -0.76V, soluble in acid, alkali-soluble, metal music is amphoteric type. Zinc dry air change hardly occurs, corrosion of zinc critical humidity greater than 70%, in the wet atmosphere and therefore can generate a thin film mainly consisting of basic zinc carbonate with carbon dioxide and oxygen effect, this membrane has a certain inhibition and so on, and zinc sulfide-containing hydrogen sulfide from the reaction of zinc sulfide; zinc chloride susceptible to erosion, it is instability in seawater.

Zinc in an enclosed or poorly ventilated, humid air conditions, when non-metallic materials in contact with the volatile matter (low molecular weight carboxylic acids, aldehydes, phenols, ammonia, etc.), zinc vulnerable to corrosion, loose white corrosion product is generated, commonly known as ” frost. ” Zinc at high temperatures, high humidity, confined conditions, and bakelite, paint, wood volatiles released contacting zinc has a tendency filamentous growth of single crystals, commonly known as “hairy.”

Standard potential than iron zinc negative, in terms of the steel is anodic coating provides reliable electrochemical protection. Use in an industrial atmosphere, rural atmosphere and ocean of the atmosphere can be selected steel products zinc as a protective layer, its relationship with the protective zinc coating life is almost proportional to the thickness. Where industrial air pollution in the atmosphere, zinc coating corrosion better than cadmium plating, at sea or in the sea opposite.

After zinc coating after chromate corrosion resistance can be improved 6–8 times. It is essential for galvanized passivation step. In the passivation film organic dye, can be used for low file protection products — decorative coating.

To reduce the thickness of zinc coating can improve corrosion resistance, at home and abroad adopt the following two measures: First, to improve the quality of the passivation film, such as blue, green, military green, black passivation instead of the conventional rainbow color passivation film , especially in military green passive film corrosion resistant; the second is a thin iron 0.3% – 0.6% Zn-Fe alloy, nickel, or 6% -10% of the Zn-Ni alloy instead of pure zinc coating, corrosion performance improvements more than three times, widely used on cars instead of galvanized steel sheet.

Zinc coating temperature not exceeding 2500C, the temperature deformation of the crystal structure of zinc, brittle, corrosion resistance decreased. There corrosion resistance, heat requirements of the parts is appropriate Zn-Ni alloy layer.

Galvanized electrolyte can be pided into two major categories of basic and weak acid, commonly used at home and abroad Have cyanide zincate zinc cyanide, zinc, galvanized ammonium salts, zinc chloride, zinc, and other sulfate. Domestically, non-cyanide zincate is still the mainstream. In recent years, due to the improved performance of galvanized additives improve, zinc chloride and low cyanide bright zinc rapid development, and ammonium galvanizing continued to decline.

Select the plating bath according to pieces of material, shape, appearance requirements may be, such as stamping small parts and complex parts, in particular the need for auxiliary anode hole or tubular member should use alkaline bath; hydrogen embrittlement sensitive parts is appropriate weak acid zinc plating solution. When the performance of two different bath, the production is very favorable.

    

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