What materials are used for seawater, acidic media, and high-temperature oil and gas in each of the three working conditions

On the procurement inquiry sheet for valve forgings, the material column often only writes three words: stainless steel. When it comes to the forging factory, these three words cannot be directly quoted - stainless steel is divided into several layers, and the price and delivery time vary greatly depending on which layer is selected.

In the product page of Fujian Mingda, only four words are given in the "raw materials" column: carbon steel, alloy steel, stainless steel, and special alloys. More than forty product pages are written the same. These four words are the first boundary of selection, and how to proceed depends on the medium, temperature, and pressure.

1、 How to divide the four words and where is the boundary of carbon steel

Carbon steel is at the bottom layer, alloy steel is subjected to temperature and pressure, stainless steel solves corrosion, and special alloy treatment is used for working conditions that conventional materials cannot withstand.

The specific brand names of these four categories are not displayed in the product page. The same type of material has different brand names under different standard systems, so when placing an order, the material should be reported together with the standard system, and not just given one category name.

The boundary of carbon steel has been clearly defined: in oil and gas, chemical, and nuclear power projects, under conditions such as medium corrosion and high temperature and pressure, ordinary carbon steel forgings are difficult to operate stably for a long time.

This statement, in turn, is the applicable boundary of carbon steel - for pipelines with conventional media, temperatures, and pressures that are not extreme, carbon steel is the lowest cost choice. Once the medium becomes corrosive or the pressure and temperature rise, it has to move up to the next layer.

2、 For the special alloy, Mingda has provided clear corresponding working conditions

This is the most specific paragraph written on the website, with each of the four types of materials having its own position:

Dual phase steel forgings have both strength and corrosion resistance, with good resistance to pitting and crevice corrosion. They are suitable for seawater and chloride ion chemical medium pipelines and are commonly used to process ball valves, valve bodies, and valve seats.

Super austenitic stainless steel forgings have stronger stability in medium temperature acidic environments and are suitable for fine chemical equipment.

Nickel based alloy forgings are resistant to high temperatures and can withstand corrosion from various strong acid media. They are commonly used in high-temperature oil and gas, and highly corrosive chemical process valves.

Titanium based alloy forgings are lightweight and have excellent corrosion resistance, making them suitable for some special chemical equipment.

In addition, the company focuses on nickel based high-temperature alloys, nickel based corrosion-resistant alloys, duplex stainless steels, super austenitic stainless steels, and heat-resistant steels in the field of special alloy forging. The alloy materials that can be processed cover nickel based, iron-based, copper based, and titanium based.

These four types of materials are further elaborated in another article on the website titled "Key Points for Selection of Special Alloy Valve Forgings", which can be compared when working on specific projects.

3、 Where is the difficulty in forging special alloys

Special alloys themselves have poor plasticity and narrow forging windows. The processing process requires control of heating temperature, deformation amount, and post forging heat treatment to avoid coarse grains or cracking of forgings.

The phrase 'narrow forging window' has a specific meaning when applied to equipment: the heating temperature needs to be controlled by a fully computer-controlled natural gas heating furnace, and Mingda is equipped with two 60T and one 40T furnaces; The deformation is achieved by using 8T and 5T electro-hydraulic hammers in conjunction with 15T and 5T operating machines and 12T multi station discharge machines. A narrow window means that if the temperature drops a little and the deformation difference is a little, this furnace may be scrapped, which cannot be done with a hammer.

The advantage of forging is that the mechanical properties of the forged parts are uniform after forming, making them suitable for long-term alternating pressure conditions.

4、 The material standards should be clearly stated during the inquiry process

There are four systems of material standards for product page labeling: ASTM, DIN, JIS, and GB.

Why mention this item separately? Because the same type of material has different brand names in these four systems, there are also differences in the requirements for chemical composition and mechanical properties. Just writing the three words' stainless steel ', the factory cannot determine which standard to supply and which standard to issue material certification according to. The project has reached the inspection stage, and the standard number on the material certificate does not match, which may cause the entire batch to get stuck.

The pressure level column is uniformly labeled on the product page as 150 to 2500LB, corresponding to PN20 to PN420.

The specification range of different parts is different. When quoting, you can compare and write:

Valve body and cover: NPS half "-48", DN15 to DN1200
Valve Seat: NPS Half "-56", DN15 to DN1400
Sphere: NPS half "-40", DN15 to DN1000
Pressure plate, valve stem, support plate: NPS2 "-24", DN50 to DN600
Fixed axis: marked as NPS Half "-12", but the DN range in the same column is written as DN600

The two sets of values in this row do not match - NPS ݪ "-12" cannot be converted to DN600. Before placing an order, it is recommended to follow the drawing markings and not directly copy the page values.

5、 What testing items are involved in material certification

The testing items for forgings include material spectrum, impact, tensile, metallographic, and hardness, along with corresponding material certification materials, for project inspection.

The corresponding testing equipment includes universal testing machines, impact testing machines, metallographic analyzers, spectrometers, and hardness testers. In terms of flaw detection, there are digital ultrasonic flaw detectors, image analysis metallographic microscopes, and AC/DC magnetic particle flaw detectors.

Among these items, spectroscopy is used to confirm whether the material composition is the type required by the order, impact and tensile tests are used to examine mechanical properties, metallographic tests are used to examine the microstructure, and hardness is the most commonly performed first-line inspection. If the purchaser wants third-party re inspection, it is recommended to raise it when placing the order, instead of waiting for delivery to make up for it.

6、 Report these seven items clearly before placing an order

Type of component: Valve body, ball, valve cover, valve seat, valve stem, fixed shaft, support plate, pressure plate, or block

Specification: DN or NPS

Pressure rating: LB or PN

Material classification and material standard system: Which one should be selected from ASTM, DIN, JIS, GB

Media, temperature, and actual operating conditions - this determines whether or not to use special alloys

Delivery status: forging blank, rough machining, or precision machining finished product

Do we need material certification and third-party retesting

The fifth item is the easiest to omit, but it is precisely the key to determining the material. The same valve body can be used for both normal temperature water and high temperature oil and gas, and the selected materials may differ by two levels, resulting in a significant price difference.

7、 It is not recommended to place orders directly according to the major categories for the four types of situations

One is to only write the material category without specifying the standard system. As mentioned earlier, this will make it difficult for the factory to determine which standard to supply and issue certificates according to.

Secondly, carbon steel is still used in high-temperature, high-pressure, and highly corrosive working conditions. It has been clearly stated that ordinary carbon steel is difficult to operate stably for a long time under such working conditions, and the saved material costs will usually be doubled and returned later.

The third is to only consider the material and not the forging ability. The forging window of special alloys is narrow, and when the same material is made in different factories, the grain size and performance can vary greatly. The equipment list and performance of similar materials are more worth looking at than the names on the material list.

Fourthly, it eliminates the need for non-destructive testing and material certification. The inspection process for projects such as nuclear power and petrochemicals is a mandatory requirement, and without supporting documents, the components cannot enter the site.

Fujian Mingda Valve Manufacturing Co., Ltd. specializes in large, medium, and small-sized free forgings and die forgings, covering valve core components such as valve bodies, spheres, valve covers, and valve seats. The raw materials are supplied in four categories: carbon steel, alloy steel, stainless steel, and special alloys. The material standards support four systems: ASTM, DIN, JIS, and GB. The delivery status can be selected as forging blank, rough machining, or precision machining. The testing includes material spectrum, impact, tensile, metallographic, hardness, and supporting material certification materials. Customization of irregular structures based on drawings is also supported.