Exactly how to prevent interior deterioration of natural gas pipe ?

For gas pipeline, internal deterioration is the electrochemical reaction of residual water and acid gas in the pipeline similar to galvanic cell and the chemical reactions that ruin the steel latticework. Both of these reactions cause the pipe wall to loosen, diminish and also pierce, which can no longer endure the stress of gas in the pipeline. In useful application, a kind of layer can not be excellent security, or can not meet the demand such as anti-corrosion, climate resistance, great look, and also as a result most a number of coating on metal surface finishing work together to create a whole system, including primer layer, the center layer, paint, finishing one or a number of times each layer respectively as required, and also there is just solitary layer such as powder layers can meet the different needs at the same time.

The anti-corrosion covering of gas pipe should have the adhering to residential or commercial properties: efficient electric as well as water insulation; Not limited by finish techniques; Good attachment to pipe surface area; Resistant to harm throughout installation, storage space and transport; Resistance to chemical medium damage; Easy to fix; Long service; Environmentally pleasant and also safe. Currently, the anti-corrosion layers for far away transportation pipes mostly include coal tar paint, 2LPE, 3LPE, merged epoxy powder (FBE), and also double-layer fused epoxy powder (FBE double-layer) layer.

Coal tar enamel.

Coal tar paint finish is the very early pre-owned covering, it's characterized by excellent insulation efficiency, low water absorption, resistance to microbial corrosion as well as plant root penetration, long life span as well as low price. Nonetheless, its mechanical stamina is reduced and also has a little appropriate temperature variety, it might leave poisonous gases and also requires strict smoke treatment. In recent times, it has been progressively replaced by other covering layers as a result of the constraint of environmental protection.


2LPE has good insulation efficiency, low water absorption, high mechanical toughness, difficult wear resistance, acid, antacids, salt and microbial deterioration, temperature adjustment resistance.

Nonetheless, there are also disadvantages: easy aging, poor adhesion with the steel tube surface, bad anti-cathodic removing performance. Electrostatic protecting of PE layer is not conducive to outside present cathodic defense.


The 3 layers of PE anti-corrosion layer integrate the advantages of high density polyethylene and fused epoxy powder. The epoxy powder is securely combined with the surface area of the steel pipeline, and the high thickness polyethylene is immune to mechanical damages. The sticky layer in between the two layers makes the 3 type a composite structure of molecular bond, which recognizes the excellent mix of corrosion resistance and also mechanical properties. It is the front runner for large natural gas transport pipeline design.

Combination adhered epoxy powder (FBE).

The PBE finish WLDSTEEL INC. has strong bonding with the surface area of the steel pipe, excellent insulation performance, high mechanical stamina, temperature level adjustment resistance as well as chemical deterioration resistance, as well as can be utilized in a range of severe settings. The major disadvantage is poor ultraviolet resistance and the thin overburden layer (0.35 ~ 0.50 mm). The double-layer FBE resembles 3PE, with great compatibility, smooth surface of the covering layer, which can stay clear of cathodic securing.

So, how does the finish shield the internal wall of the gas pipeline? We currently recognize that metal corrosion results from the activity of the environmental medium on the steel surface area to produce electrochemical reaction or chemical reaction, the effect of the finish on the pipeline is accomplished by preventing the above responses:.

( 1) Shielding: Many layers on acid, antacids, salt as well as various other harsh media reveal chemical inertia, and also the high dielectric consistent to stop the formation of deterioration circuit, so the metal surface area coating to the steel surface area as well as the atmosphere isolation and also securing the corrosive tool. It needs to be mentioned that the polymer layer is breathable as well as very closely pertaining to its structure.

( 2) Passivation slow-moving release: With the help of antirust pigment in the coating as well as the metal surface area reaction, make it passivation or generate protective materials; In addition, many oils can also work as organic corrosion inhibitors by creating deterioration products under the catalytic activity of metal soaps.

( 3) Electrochemical defense: The layer possibility is less than iron steel filler (such as zinc) will certainly sacrifice the cathodic protection of the anode, and the atmospheric rust products of zinc alkali zinc carbonate is reasonably secure, can be shut, plug the final gap.

So exactly how to stop the corrosion of the internal wall surface of the gas pipe? We can prevent by doing this: to start with, the gas drawn out from the ground experiences a series of processes such as desulphurization and dehydration, before it goes into the long-distance pipeline. Second of all, the efficient inner finish of the pipeline can reduce deterioration, gas transmission resistance and also cleansing time.

Exactly how to bond ASTM A333-GR6 reduced temperature steel pipeline

ASTM A333 Grade 6 is one of one of the most frequently made use of low temperature level steel pipes, its minimal solution temperature level is -70 ℃, generally in normalizing or stabilizing and solidifying problem. ASTM A333-GR6 steel has reduced carbon content, superb reduced temperature level toughness, plasticity and welding efficiency, and also little quenching as well as chilly splitting tendency. The low temperature toughness, namely the capability to prevent weak failure from taking place and also expanding at reduced temperature level, is one of the most crucial aspect affecting its welding efficiency.

Common welding techniques for reduced temperature level steel consist of arc welding, immersed arc welding, argon arc welding and more. MIG welding is one of the most extensively made use of automated or semi-automatic welding technique in low temperature level steel welding. Its welding warmth input is 23-40kJ/ cm. According to the mode of droplet transfer, it can be separated right into brief circuit transition procedure (reduced warm input), jet transition process (high warmth input) and pulse jet shift procedure (the greatest warm input). Short-circuit shift MIG welding may have the defect of not enough melting deepness or bad fusion. In order to make the arc more focused as well as obtain acceptable penetration deepness, CO2 or O2 can be contributed to the pure argon shielding gas. The particular amount of addition must be identified according to the steel grades.

Welding material

Welding products (including electrode, wire and also flux, and so on) will be selected according to the welding approach embraced, joint kind as well as groove form and also demands. For reduced temperature level steel, one of the most crucial thing to focus on is to make the weld steel have enough low temperature sturdiness to match the base steel and also reduce the hydrogen diffused in it. Normally, ER80S-Ni1 argon arc welding cord is used.

Welding process

In welding, I-Shape port is made use of for pipes with diameter much less than 76.2 mm, and also complete argon arc welding is performed. For the V-groove of pipe with diameter greater than 76.2 mm, argon arc support as well as multi-layer filling are taken on, or full argon arc welding That's relies on particular pipeline WLDSTEEL size and also pipeline wall surface density.

( 1) Preheating prior to welding.

When the ambient temperature is lower than 5 ℃, the steel pipeline should be preheated, and also the pre-heating temperature is 100 ~ 150 ℃. The pre-heating array is 100 mm on both sides of the weld; Heated by oxyacetylene flame (neutral fire), the temperature was measured evenly at a range of 50 ~ 100 mm from the weld facility for better temperature control.

( 2) Postweld heat therapy

In order to enhance the notch strength of cryogenic steels, many steel tubes have actually been solidified and also toughened up, to make sure that post-weld warmth treatment is not typically required for cryogenic steels, with the exception of thicker weldments or in serious conditions.

If special parts need to be heat dealt with after welding, according to the home heating price, consistent temperature time as well as cooling price of the heat therapy after welding, the following arrangements have to be strictly implemented:

When the temperature increases above 400 ℃, the home heating price will not go beyond 205 × 25/ δ ℃/ h, as well as will not exceed 330 ℃/ h. Constant temperature level time should be 1 h per 25 mm thickness continuous temperature level, as well as will not be less than 15 min, optimum and minimum temperature level throughout the temperature ought to be lower than 65 ℃. After constant temperature level, the cooling rate will not be more than 65 × 25/ δ ℃/ h, and also shall not be higher than 260 ℃/ h, and all-natural cooling can be done listed below 400 ℃.

Tips for welding ASTM A333 Grade 6 tubes

( 1) Preheat strictly according to the arrangements, control the temperature in between the layers, the temperature between the layers is regulated at 100 ~ 200 ℃.

( 2) Strictly control line energy, small current, low voltage, quick welding.

( 3) complete infiltration process need to be adopted, and also the operation mode of brief arc and no swing.

( 4) The residual elevation of the weld is 0 ~ 2mm, and the size of each side of the weld is less than 2mm.

( 5) Nondestructive testing can be performed at the very least 24 hours after the appearance evaluation of the weld is certified.

The alloying element in low temperature level steel

Reduced temperature level steel has superb toughness and strength in low temperature atmosphere, excellent welding efficiency, machining performance and deterioration resistance, are typically specified in the minimum temperature of a particular worth of influence strength in the requirement. In reduced temperature steels, aspects such as carbon, silicon, phosphorus, sulfur as well as nitrogen degrade the toughness at reduced temperature, amongst which phosphorus is thought about to be one of the most dangerous and also ought to be dephosphorized at reduced temperature in early smelting. Mn, nickel and also other aspects can improve the toughness at low temperature level. With the rise of nickel web content by 1%, the critical transition temperature of brittleness can be reduced by about 20 ℃. Low temperature strength, i.e. the ability to avoid brittle failing from happening and spreading out at reduced temperatures, is the most essential element. Today we present the influence of alloying aspects on the low temperature toughness of steel:


With the boost of carbon content, the fragile change temperature level of steel boosts quickly and also the weldability decreases, so the carbon material of low-temperature steel is limited to much less than 0.2%.


The manganese exist in steel with the form of solid service as well as can certainly improve the toughness of steel at low temperature. In addition, manganese is an aspect that expands the Austenite area and decreases the change temperature level (A1 and also A3). It is very easy to get great and pliable ferrite and pearlite grains, which can make best use of the impact power as well as decrease the breakable transition temperature. Because of this, the Mn/C proportion should be at least equal to 3, which can not just decrease the weak change temperature level of steel, but likewise make up for the decline in mechanical residential properties caused by the decrease in carbon content due to the rise of Mn.


Nickel can decrease the brittleness propensity and also considerably decrease the breakable transition temperature. The impact of nickel on improving the reduced temperature strength of steel is 5 times that of manganese. The brittle shift temperature reduces by 10 ℃ with the increase of nickel web content by 1%. This is because the nickel does not react with carbon, but all dissolved into the strong option and the conditioning, nickel also makes the steel eutectoid point to the lower left, as well as lower the eutectoid point of carbon material and also phase modification temperature level (A1 as well as A2), so compared to other carbon steel has the same carbon web content, the number of ferrite reduction and improvement, while the pearlite boost.

P 、 S 、 Pt 、 Pb 、 Sb.

These aspects are damaging to the reduced temperature sturdiness of steel. They create partition in steel, which minimizes the surface area power of grain limit, minimizes the resistance of grain limit, and causes the weak crack to originate from grain boundary and also proliferate along grain boundary till the fracture is complete.

Phosphorus can WLDSTEEL enhance the stamina of steel yet enhance the brittleness of steel, especially the brittleness at reduced temperature level. The breakable change temperature level is undoubtedly enhanced, so the content of phosphorus need to be purely limited.

H, O, N.

These elements will raise the breakable change temperature of steel. Reduced temperature level sturdiness can be improved by deoxidizing eliminated steels with silicon and light weight aluminum. Yet silicon boosts the weak shift temperature of steel, so light weight aluminum killed steel has a lower fragile shift temperature level than silicon eliminated steel.

What happens when steel overheating?

If the home heating temperature level is too high, the metal Austenite grain slowly grows as well as transforms can compromise the grain border, this process is referred as overheating. When the steel is warmed to near solidus or solid-liquid phase temperature array, after a particular temperature in the crude Austenite grain boundary on the chemical composition of the evident modifications have actually occurred not only (mainly partition of sulfur as well as phosphorus), and also partial or entire grain border burning-out phenomenon happens, thus on the grain limit created rich sulphur, phosphorus fluid, created in the process of cooling down rich sulphur, phosphorus burning-out layer and also form S, P of iron and also other fragile sedimentary facies, the boundary triggered by severe lower steel tensile plasticity and also impact toughness of the phenomenon. Over-heating can lead to intergranular cracks.

Overburning is a process in which when the steel is heated at a temperature level near to the melting temperature level or www.wldsteel.com is seriously overheated, not just the austenite grains are coarse, yet likewise the grain boundaries are deteriorated by neighborhood oxidation or melting.

Over dissolved or over-burned is a a procedure like this: in which when the steel is heated at a temperature near to the melting temperature or is seriously overheated, not just the Austenite grains are coarse, yet likewise the grain boundaries are deteriorated by neighborhood oxidation or melting. Steel properties seriously tatty, quenching crack, overburned tissue can not be recouped yet just be ditched, so we should attempt to prevent it.

Overheat and also over-melted are very comparable, the major reasons for their generation are: high home heating temperature level, or long time in the high temperature resource; The final temperature level of warm handling is expensive or the home time in the heat area is as well long; There are low melting point components or many low melting point incorporations in the alloy. The overmelted temperature level of steel is usually loads to a hundred degrees greater than the overheating temperature level. On top of that, the difference in between over-melt as well as getting too hot also depends on:

1. Various grains

Overheat: thick grains can be improved by warm therapy in the future.

Over-melt: oxidation in between grains, an irreversible problem.

2. Various temperature levels

Overheat: the temperature exceeds the normal stage transition temperature level, less than the temperature level of overmelting.

Over-melt: temperature level goes beyond the eutectic temperature at the low melting factor of the alloy.

3. Different metallographic structure

Overheat is the sensation of metal grain coarseness caused by extreme home heating temperature or heat holding time. Carbon steel and bearing steel often tend to have Widmannian framework after overheating;

The α stage (or Ferrite) of Austenitic stainless-steel boosts substantially after overheating. The superheated microstructure of high alloy steels is typically established by the attributes of sub-carbide angularity. The getting too hot that can be eliminated by typical warmth therapy process is called unsteady getting too hot. General stabilizing, annealing or quenching therapy can not entirely get rid of the overheating known as secure getting too hot.

Throughout stable getting too hot, in addition to the coarse austenite grains or the combined austenite grains, the heterogeneous bits such as sulfide (Mns) are precipitated along the original austenite grain border.

The even more sulfide particles there are, the more steady the proaustenite grain border becomes. Although the steel is Austenitized again in the later normalizing as well as quenching, the distribution, shapes and size of the particles such as sulfide on the original Austenitic grain boundary will not be changed to much extent, creating steady overheating. The mechanical buildings of superheated structures, specifically the influence durability (at reduced temperature level), are minimized as a result of the coarse grain dimension.

Over-melt ways that the heating temperature level is more than that of overheating, however there is no rigorous temperature level restriction, and also it is typically characterized by oxidation as well as melting at grain boundaries. Grain border melting and also significant oxidation of carbon steel throughout overburning; When device steel mores than shed, the grain boundary is thawed as well as the leitsite shows up. Over-burned steel will break during building and also the random sample will show up light gray. Coarse grain, the extra oxygen in the heating system gas, the longer the heating time, the much more simple to overburn. At the steel-making temperature, oxides and also sulfides have a particular solubility in the steel, and non-metallic inclusions will certainly be precipitated according to a specific regulation throughout the solidification process of molten steel.

Currently, low magnification examination, metallographic analysis and also fracture evaluation are extensively used in the decision of overheating and also over-melt, among which metallographic analysis is commonly made use of.

The distinction in between overheating as well as over-melt is whether the Austenite grain boundary is compromised. The easiest approach is to observe the crack surface morphology (that is, the steel fracture takes place throughout solution).

Getting too hot is generally brought on by too much grain growth which can be enhanced by future warm therapy. Over-melt is the oxidation between grains, which is an irreversible problem.

What’s 9% Ni steel

9% Ni steel is W( Ni) -9% reduced carbon medium alloy satiated and tempered steel created by the American International Nickel Company in 1944. Its structure is Martensite as well as Bainite. This steel has excellent sturdiness and also high toughness at extremely reduced temperature level, the thermal expansion coefficient is tiny compared to Austenitic stainless-steel as well as aluminum alloy, the lowest temperature level can get to a 196 ℃. The 5% Ni steel developed based on 9Ni steel likewise has good low temperature strength at the reduced temperature of -162 ~ -196 ℃.

The primary attributes of this steel are high nickel content, high pureness, high stamina, high low temperature impact toughness, good weldability. In 1952, the first 9Ni steel storage tank in the world was put into use in the United States. In 1960, the research confirmed that 9Ni steel without post-weld anxiety alleviation warmth therapy could be utilized safely. Ever since, 9Ni steel has become one of the primary products used in the manufacture of huge cryogenic storage tanks. The first LNG tank built in Japan in 1969 has a maximum ability of 20 × 104m ³.

The 9% Ni steel plate is the frequently used form for this steel, and also the steel plate have some spec worldwide such as ASME: SA-353, EN 10028, JIS G3127, GB 24510 and others.

EN 10028-4: X8Ni9+ NT640/ X8Ni9+ QT680.

JIS G3127: SL9N520/SL9N590.

ASME: SA-353/ SA-553-1.

GB 24510: 9Ni490/ 9Ni590A.

The mechanical residential or commercial properties of 9Ni steel at reduced temperature level mostly depend upon its chemical structure, especially the components of Ni as well as C. Additionally, the sturdiness of 9Ni steel likewise depends upon the purity and also microstructure of the steel. The 8.50 ~ 9.50 Ni web content guaranteed the hardenability to a particular level. The decrease of carbon content can significantly lower the precipitation of carbides in toughened up martensite, therefore boosting the low temperature strength, while the high carbon content will cause significant wear and tear of welding wldsteel.com homes and chilly breakable properties. Consequently, in the alloying procedure, the material of C need to be strictly controlled to maintain it in the low carbon range, and also at the very same time, the content of P, S, Mn, Mo, Cr and also other alloying elements need to additionally be managed in the low range. The material of alloying elements and impurity is an essential variable influencing the breakable change temperature of 9Ni steel.

We understand that the liquefaction temperature level of natural gas is -162 ℃, and also the volume of melted gas (LNG) is 1/600 of the gaseous state, which has greater demands on the product of LNG tank. Presently the materials utilized in LNG container mainly are 9 Ni steel, 5 Ni, Austenitic stainless steel, Aluminium magnesium alloy steel, and so on, as well as the most affordable temperature level can reach 9 Ni steel – 196 ℃, its high stamina, outstanding reduced temperature level strength, great welding performance, simple to refining advantages, making it widely utilized in the manufacture of LNG container and also transport ships, is the most effective of the cryogenic atmosphere using the sturdiness of products.