The Material Of The Pipeline

Application: Used for gas, water and oil transportation in petroleum and natural gas industry

API SPEC 5L-2011 (Pipeline Specification), developed and published by the American Petroleum Institute, is used worldwide. The main material of the tube is L245, L290, L360, L415, L480, GR.B, X42, X46, X56, X65, X70, X80, X100 and other steel grade.

Stainless Steel Pipe Welding Matters

1. It is generally suitable for welding of thin steel pipe below 6mm, with the characteristics of beautiful and elegant weld molding and small welding deformation.
2. The maintenance gas is argon with the purity of 99.99%. When the welding current is 50-50A, the argon flow rate is 8-10L/min, and when the current is 50-250A, the argon flow rate is 2-5L/min.
3. The length of the tungsten pole protruding from the gas nozzle is 4-5mm, 2-3mm in the place of poor masking such as fillet welding, 5-6mm in the place of deep grooving, and the interval from the nozzle to the operation generally does not cross 5mm.
4. In order to prevent the appearance of welding pores, it is necessary to clean up the welding parts if there is rust and oil.
5 Welding arc length, welding shallow steel, with 2-4mm is the best, and stainless steel welding, with 3mm is the best, too long maintenance results are not good.
6. When docking the bottom, in order to prevent the back of the bottom weld passage from being oxidized, the back also needs to implement gas maintenance.
7. In order to maintain the welding pool well with argon and facilitate the welding operation, an Angle of 80-85° should be connected between the middle line of the tungsten pole and the workpiece at the welding place, and the general Angle between the filler wire and the workpiece should be as small as possible, generally 0°.
8. Windproof and ventilation. In windy places, please choose the method of retaining the net, and in the room, the appropriate ventilation method should be selected.

Classification Of Galvanized Pipes

Galvanized pipe, also known as galvanized steel pipe, is divided into hot dip galvanized and electric galvanized. Hot dip galvanizing layer thick, uniform coating, strong adhesion, long service life. Electroplating cost is low, the surface is not smooth, corrosion resistance than hot dip galvanized pipe is poor.
Galvanized steel tube: hot dip galvanized steel tube steel tube substrate and molten plating solution composite physical, chemical reaction, forming a dense zinc iron alloy layer corrosion resistant structure. The alloy layer is integrated with the pure zinc layer and the steel tube substrate. Therefore, its corrosion resistance is strong.
Galvanized steel pipe: The zinc layer of cold galvanized steel pipe is an electric coating, and the zinc layer is separated from the steel pipe substrate. The zinc layer is very thin, and the zinc layer is simply attached to the steel tube substrate, which is easy to fall off. As a result, its corrosion resistance is poor. In new homes, the use of cold galvanized steel pipes as water supply is prohibited

Introduction To Vessels Steel Plate

In fact, the vessels is a big category among many steel plates, which has very special composition and many excellent properties. At present, this kind of vessels plate is mainly used to make pressure vessels in the market. For different situations and different uses, the corresponding materials to be made are also different.

This kind of device has a relatively large number of brand names in the current market, and its application scope corresponding to different delivery states is also different. In the following small series, users will be specifically introduced about the vessels plate.

Introduction to the use of the vessels

vessels plate is now widely used in petroleum, chemical industry, power stations and boilers, etc. It is used to manufacture reactors, heat exchangers, separators, spherical tanks, oil and gas tanks, liquefied gas tanks and nuclear reactor pressure shells, etc. In addition, this material is also used to manufacture boiler drums, liquefied oil and gas cylinders, high-pressure water pipes of hydropower stations, spiral cases of water turbines and other equipment or components. Moreover, this material has a very broad market at home and abroad.

Introduction of delivery status of vessels

There are four main delivery states of plates, namely quenching, normalizing, annealing and tempering. Moreover, the main application scope of each delivery state is also different.

Main application scope of normalizing

Compared with low carbon steel, the hardness of vessels plate after normalizing is higher than that after annealing, and its toughness is relatively good.

Can be used with medium carbon steel.

Used for tool steel, carburized steel and bearing steel.

Used for steel castings, normalizing, it has a good refining effect on the microstructure of steel materials.

It is used for large forgings and nodular cast iron, which can improve its hardness, strength and wear resistance.

Characteristics of the plate after tempering

1. After tempering, the structural stability of the vessels plate can be improved, so that the size and performance of the workpiece can be kept in a very good state.

2. After tempering, for the product made of vessels plate, it can also eliminate the internal stress in the container plate, thus changing the service performance of the device.

3. The mechanical properties of the vessels plate can be well adjusted, so as to meet the requirements of application in various fields.

Plate is a kind of important steel plate used for manufacturing various boilers and their accessories, and it is also the most widely used and used special steel plate for pressure vessels in China at present.

Precautions For Metal Pipeline Construction In Winter

Metal pipeline construction points for attention in winter, the biggest characteristic of winter construction I think is that the temperature is relatively low, in the welding operation must pay attention to the temperature, the need to determine the temperature of the welding position before welding, in the case of lower than the process requirements of the temperature, the base metal must be preheated before welding. Attention should be paid to the thermal insulation problem after welding in winter. Attention should be paid to keep the materials dry in rain and snow. Measures should be taken during the welding construction in winter. If the temperature is above -5 degrees Celsius,  do some conventional drying and insulation. If the temperature is too low or the board is too thick, we need to preheat and pay attention to the insulation between layers.

Winter construction main technical measures

1. Pipe welding should be preheated in strict accordance with the requirements, and the pipe should be put into the closed workshop for heating in advance.

2. when the ambient temperature is below 5℃, it is not suitable for hydraulic test; The water of the pipeline that has been tested by hydraulic pressure should be drained out of the pipe in time and the pipe mouth should be temporarily blocked.

3. should try to avoid the pipeline pressure test in winter, if it must be in winter pressure test, to minimize the water filled pipeline exposure to the natural environment time, in line with the requirements of the specification under the premise, the test time should be as short as possible, after the test, to drain the water in the pipeline in time and maximize the blow dry.

4.The amount of prefabrication should be increased as much as possible to reduce the welding workload on site.

5. The wind speed during welding shall not exceed the following provisions; otherwise, windproof measures shall be taken:

A manual arc welding is 8m/s;

B hydrogen arc welding, carbon dioxide gas welding 2m/s

6.The relative humidity of the environment within 1m welding arc shall not be greater than 90%.

7. the welding environment temperature should be able to ensure that the welding parts required sufficient temperature and welder skills will not be affected.

8. Welding process requirements:

A When the ambient temperature is below 0℃, welding joints without preheating requirements, except austenitic stainless steel, should be preheated to more than 15℃ within 100mm of the initial welding site.

5 Nondestructive Testing Methods For Steel

The nondestructive testing of steel mainly involves ray testing, ultrasonic testing, magnetic particle testing, penetration testing and eddy current testing.

 1. Radiographic Detection (RT)
X-ray testing refers to the non-destructive testing method that uses X-ray or gamma ray to penetrate the specimen and uses film as the equipment for recording information. This method is the most basic and widely used non-destructive testing method.

2. Ultrasonic Detection (UT)
Ultrasonic testing is suitable for nondestructive testing of metal, nonmetal and composite materials. It can detect the internal defects of the specimen within a wide thickness range. For metal materials, can detect the thickness of 1 ~ 2mm thin wall pipe and plate, can also detect several meters long steel forgings; Moreover, the defect location is more accurate and the detection rate of area defects is higher. High sensitivity, can detect the internal size of the specimen is small defects; And the detection cost is low, the speed is fast, the equipment is light, harmless to the human body and the environment, the field use is more convenient.

3. Magnetic Particle Detection (MT)
Principle of magnetic particle detection is magnetized ferromagnetic material and workpiece, but because of the discontinuity, the magnetic field lines on the surface of the workpiece surface and near local distortion and a leakage magnetic field is generated, adsorption on the surface of the magnetic powder and magnetic marks visible form in the right light visual, showing the location, shape and size of discontinuity.

4. Penetration Testing (PT)
The principle of penetration detection is that after the surface of the part is coated with permeant containing fluorescent dye or colored dye, under the action of capillary, after a period of time, the permeable liquid can penetrate into the surface opening defects; After removing the surface excess penetrant, painted on the parts surface imaging agent again, also, under the action of capillary, imaging agent will attract defects in penetrants, penetrating fluid flow back into the imaging agent, in a certain light (uv light or white light), defect penetrant traces are reality, (yellow-green fluorescence or bright red), Thus, the morphology and distribution of defects are detected.

5. Eddy Current Testing (ET)
Eddy current testing places a coil with alternating current on a metal plate or outside a metal tube under test. At this time, an alternating magnetic field will be generated in and around the coil, resulting in a vortex-like induced alternating current in the specimen, called eddy current. The distribution and size of eddy current are not only related to the shape and size of the coil and the size and frequency of the AC current, but also depend on the conductivity, permeability, shape and size of the specimen, the distance from the coil and whether there are cracks on the surface.

API5L X52N X56Q PSL2 OD24″ Seamless pipeline

our factory have Φ720 rolling can produce big size seamless pipes directly . such as API5L X65QS PSL2 OD610*12.7mm by hot rolled producing Length 12m

API5L X65QS PSL2 chemical composition:

API5L X65QS PSL2 Mechanical Properties

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Carbon steel material for Hydrogen sulfide corrosion applications

Hydrogen sulfide H₂S is an inorganic compound that is colorless, flammable, soluble in water acid gas, hydrogen sulfide corrosion refers to the oil and gas pipeline containing a certain concentration of hydrogen sulfide (H2S) and water corrosion.  H₂S dissolves in water and becomes acidic, leading to electrochemical corrosion and local pitting and perforation of pipelines. The hydrogen atoms generated in the corrosion process are absorbed by the steel and enriched in the metallurgical defects of the pipe, which may lead to the embrittlement of the steel and the initiation of cracks, leading to cracking. The pipeline and equipment of acid oil and gas fields containing H₂S have appeared many times sudden tearing or brittle fracture, welding zone cracking and other accidents, which are mainly caused by hydrogen-induced cracking (HIC) and sulfide stress cracking (SSC).

The factors affecting the corrosion of H₂S include hydrogen sulfide concentration, PH value, temperature, flow rate, carbon dioxide and chloride ion (C1-) concentration, etc. A wet hydrogen sulfide stress corrosion environment is constituted if the following conditions are met:

  • Medium temperature is not greater than 60+2P ℃, P is the medium gauge pressure (MPa);
  • B partial pressure of hydrogen sulfide is not less than 0.35mpa;
  • The medium contains water or the medium temperature is lower than the dew point temperature of water;
  • Medium with PH less than 9 or cyanide.

The results show that for the alloy steel when the strength or hardness of the steel is the same, the microstructure of uniform distribution of small spherical carbides can be obtained by high temperature tempering after quenching, and the resistance to H2S corrosion is better than that after tempering. The shape of inclusions also matters, especially the shape of MnS, because MnS are prone to plastic deformation at high temperatures, and the sheet MnS formed by hot rolling cannot be changed during subsequent heat treatment.

Elements Mn, Cr and Ni are added to the carbon steel to improve the hardenability, especially Ni. It is generally believed that Ni element is beneficial to the toughness of alloy steel, but the hydrogen evolution reaction overpotential of Ni steel is low, the hydrogen ion is easy to discharge and reduce to accelerate the hydrogen precipitation, so the resistance of Ni steel to sulfide stress corrosion is poor. In general, carbon steel and alloy steel should contain less than 1% or no nickel. Elements such as Mo, V, Nb, etc. that form stable carbides in steel.

ISO 15156-2, ISO15156-3 or NACE MR0175-2003 have limited the environmental conditions to avoid the occurrence of stress corrosion. If these conditions are not met, HIC and SSC tests shall be performed, and other relevant standards shall be met. The American Corrosion Institute (NACE) MR-01-95 states that to prevent sulfide stress corrosion cracking (SSCC), ordinary steel (nickel content less than 1%) with a hardness below Rockwell HRC22 or tempered chrome-molybdenum steel with nickel content less than HRC 26 shall be used.

In addition, there are other restrictions:

  • Impurities in steel: sulfur ≤ 0.002%, P≤0.008%, O≤ 0.002%.
  • Hardness is not more than 22HRC, yield strength is less than 355MP, tensile strength is less than 630MPa
  • The carbon content of steel should be reduced as much as possible under the condition of satisfying the mechanical properties of steel plate. For Low carbon steel and carbon-manganese steel: CE≤0.43, CE=C+Mn/6; For low alloy steel: CE≤045 CE=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15

Steel plate:SA387 Gr11(HlC), SA387 Gr12(HlC), SA387 Gr22(HlC), SA516 Gr65(HlC), SA516 Gr70(HlC);

Steel pipe: API 5CT H40, J55, L55, C75(1,2,3), L80(type 1), N80(type Q/T), C95(type Q/T), P105, P110 Q/T); API 5L grade A, grade B, X42, X46, X52; ASTM A53, A106(A, B, C)

The avaiable carbon Steel pipe and plate for H₂S application

Welding of Ultra-supercritical boiler material

Heat-resistant steel refers to the steel that works at high temperature and has excellent thermal strength and thermal stability. Thermal strength refers to the ability to resist creep and fracture at high temperature, and thermal stability refers to the ability to resist oxidation and corrosion of gaseous media at high temperature. People usually refer to the heat-resistant steel with thermal strength as heat-resistant steel and heat-resistant steel with thermal stability as heat-stable steel. Heat-resistant steels are mainly used in power and energy engineering, such as in the manufacture of oil refining equipment, boilers, nuclear vessels, steam turbines, synthetic chemical vessels, aerospace equipment and other high-temperature processing equipment. It should be noted that many stainless steels (309, 310H) also have heat resistance and are sometimes referred to as “heat resistant stainless steel”.

The welded joints of heat resistant steel shall have substantially the same high temperature oxidation resistance as the base metal. The alloy composition and content of weld metal should be basically consistent with the base metal, such as Cr, Mo, W and other major elements, while impurities such as P and S should be controlled at a low level as far as possible to reduce the tendency of hot crack. In order to improve the weldability, the C content of the welding material can be slightly lower than that of the base metal to ensure the high temperature performance. The strength of the weld metal shall be similar to that of the base metal to be welded. Heat-resistant steel welded joints shall not only have short-term strength at room temperature and high temperature basically equal to that of the base metal, but also, more importantly, have high temperature creep properties similar to that of the base metal. The performance requirements of new heat-resistant steel joints for ultra-supercritical boilers are shown in the following table.

GradesT.S σb  MPaY.Sσs  MPaElongation δ%AkvJAllowable stress at operating temperature,MPaHardness, HB
P12263053017%3164 (620℃)225~270

Although most of heat resistant steel welding structure is working under high temperature, but the final inspection for pressure vessels and piping requirements, usually at room temperature to 1.5 times the working pressure experiment hydraulic or pneumatic pressure test, the operation of pressure equipment or maintenance have to undergo the cold start process, so the heat resistant steel welding joint is also should have certain resistance to brittle fracture. For martensite and austenite heat resistant steels, the content of δ Ferrite in the deposited metal should be strictly controlled to ensure the creep property of the welded joints during the long time running at high temperature.

P92/T92, P122/T122 martensitic steel welding

Both P92 and P122 are martensitic steels, which have cold cracking tendency and hot cracking tendency during welding. In order to prevent cold cracks in welding, it is necessary to preheat before welding. The preheat temperature is not less than 150℃ for TIG welding and not less than 200℃ for electrode arc welding and submerged arc welding. In order to prevent hot crack and coarse grain, the welding line energy should be strictly controlled during the welding process, the interlayer temperature should be less than 300℃, and the tungsten electrode argon arc welding with small welding heat input is preferred. Multilayer and multi-pass welding should be paid attention to when welding electrode arc welding. The welding pass thickness should not be greater than the electrode diameter. The welding pass width should not be more than 3 times the electrode diameter and it is recommended that the electrode diameter should not be more than 4mm.For the workpiece with large wall thickness, submerged arc welding can be used for welding, but fine wire submerged arc welding should be used, and the diameter of the welding wire should be less than 3mm. When welding T122 and T92 small diameter tubes, the back side should be filled with argon during the whole welding process. For large-diameter thick-walled pipes, argon gas protection is required on the back of the first three layers of welds at the root. After weld welding, use asbestos insulation and slow cooling and stay between 100 ~ 150℃ for at least 1 ~ 2 hours, until the metallography is completely transformed into martensite, then can carry out post-weld heat treatment. For the wall thickness of the workpiece is greater than 40mm, after welding with asbestos insulation slow cooling, 100 ~ 150℃ at least stay 1 ~ 2 hours, if not immediately heat treatment, should be heated to 200 ~ 300℃ insulation 2 hours and then slow cooling to room temperature.

SUPER 304H, SA-213 TP310HCBN Austenitic steel welding

Austenitic steel has good weldability and no cold cracking tendency, so it does not need preheating. However, austenitic steel has hot cracking tendency during welding, so attention should be paid to the control of welding heat input and interlayer temperature. In the welding process, the welding method of welding line energy is smaller, such as manual TIG, automatic cold wire TIG welding or hot wire TIG welding. Generally, the interlayer temperature should be controlled not more than 150℃. For automatic cold wire TIG welding or hot wire TIG welding, the continuous welding process requires interlayer water cooling of the welded weld. In order to prevent intergranular corrosion, the chloride ion content in the cooling water should be controlled. In order to prevent the oxidation of alloying elements in the high temperature zone, the back surface should be filled with argon during the whole welding process. In order to ensure good fusion on both sides of groove, groove Angle of austenitic steel should be larger than that of general ferrite steel. For dissimilar steel welding with ferrite materials, ernicR-3 or EnICRFE-2 welding wire or electrode is recommended. When dissimilar steel is welded (with ferrite steel) and used at high temperatures, the expansion coefficient of both materials must be taken into account.


What is the creep-resistant steel used for?

Molybdenum has been a key alloying element in creep resistant ferrite steels operating at temperatures up to 530°C. The main applications of creep resistant steel are in power plants and petrochemical plants, where steam turbines require large forgings and castings, and pressure vessels, boilers and piping systems require tubes, plates and accessories of all kinds.In addition to high temperature creep strength, other material properties such as hardenability, corrosion resistance and weldability are also important. The relative importance of these properties depends on the specific application of the material. For example, large turbine rotors need steel with good hardenability, and power plant piping systems must be weldable. Even so, the alloys used in these different applications all use the same principles to improve creep strength.

Molybdenum in solid solution can reduce the creep rate of steel very effectively. When used at high temperatures, molybdenum slows the agglomeration and coarsening of carbides (ostwald’s ripening). Quenching and tempering produce a microstructure composed of upper bainite, resulting in the best results in high temperature strength. For coal-fired power plants, the efficiency of subcritical generating sets is less than 40 percent. Future ultra-supercritical (USC) plants are expected to be more than 50 percent efficient, reducing the carbon dioxide emissions per kilowatt-hour of electricity produced by almost half. Creep resistant ferrite steel is still commonly used in power plants, oil refineries and petrochemical plants worldwide. Components include seamless tubes for hot water boilers and superheaters, boiler drum, collector, pumps and pressure vessels for high temperature purposes, and steam turbine spines over 2 meters in diameter and over 100 tons in weight. This steel can be classified as C-Mn steel, Mo steel, low alloy C-RMO steel and 9-12% Cr steel.

Plant type Subcritical(Over 300000 kw)
Water wall :A192, SA-106B, SA-106C,
Overheating: T11/P12,P22/T22,T23, T91,T92
Reheater: P11,T23,T91,T92
Economizer: A192
Header and steam pipe: A192, T12, P12
Supercritical(SC)(Over 600000 kw)
Overheating: T22, T23, T91, T92, TP347H, TP347HFG, SUPER304H, HR3C
Reheater material: P12,T23,T91,T92,TP347H,TP347HFG,SUPER304H,HR3C
Economizer materials : A192, SA210C
Header and steam pipe: P11,P91, P92
Ultra-supercritical(USC)(Over 660000 kw)
Overheating material: T22,T23,T91,T92,TP347H,TP347HFG, SUPER304H, HR3C
Reheater: P12, T23, T91, T92, TP347H, TP347HFG, SUPER304H, HR3C
Economizer materials : A192, SA210C
Header and steam pipe: P11,P91,P92