What is API American Petroleum Institute?

​​​​​​API represents all segments of America’s oil and natural gas industry. Its nearly 600 members produce, process and distribute most of the nation’s energy. The industry supports millions of U.S. jobs and is backed by a growing grassroots movement of millions of Americans. API was formed in 1919 as a standards-setting organization. In our first 100 years, API has developed more than 700 standards to enhance operational and environmental safety, efficiency and sustainability.

What is API Standard?

American Petroleum Institute (API) standards advocate proven, sound engineering and operating practices and safe, interchangeable equipment and materials from drill bits to environmental protection. Included are manuals, standards, specifications, recommended practices, bulletins, guidelines and technical reports.

What is API Certified?

API certified inspectors and personnel are recognized worldwide as professionals who are fully knowledgeable of the relevant industry inspection codes and standards, and who are capable of performing their jobs in accordance with the latest and most acceptable industry inspection practices.

Valve Standards Defined by the American Petroleum Institute (API)

API 6D

Specification for Pipeline Valves, API Specification 6D is an adoption of ISO 14313: 1999, Petroleum and Natural Gas Industries-Pipeline Transportation Systems-Pipeline Valves. This International Standard specifies requirements and gives recommendations for the design, manufacturing, testing and documentation of ball valves, check valves, gate valves and plug valves for application in pipeline systems.

API 600

Bolted Bonnet Steel Gate Valves for Petroleum and Natural Gas Industries – Modified National Adoption of ISO 10434:1998.

API 602

Compact Steel Gate Valves – Flanged, Threaded, Welded, and Extended-Body Ends. The standard covers threaded end, socket-welded end, butt-welded end, and flanged end compact carbon steel gate valves in sizes of NPS4 and the smaller.

API 609

Butterfly Valves: Double Flanged, Lug Type and Wafer Type. The standard covers design, materials, face-to-face dimensions, pressure and temperature ratings, and examination, inspection, and test requirements for gray iron, ductile iron, bronze, steel, nickel-base alloy, or special alloy butterfly valves that provide tight shutoff in the closed position and are suitable for flow regulation.

API 594

Check Valves: Flanged, Lug, Wafer Type and Butt-welded. API Standard 594 covers design, material, face-to-face dimensions, pressure and temperature ratings, and examination, inspection, and test requirements for two types of check valves.

API 598

For Valve Inspection and Testing, the standard covers inspection, supplementary examination, and pressure test requirements for both resilient seated and metal-to-metal seated gate valves, globe valves, plug valves, ball valves, check valves, and butterfly valves, pertaining to inspection by the purchaser and to any supplementary examinations the purchaser may require at the valve manufacturer’s plant.

API 607

Fire Test for Soft-Seated Quarter Turn Valves, the standard covers the requirements for testing and evaluating the performance of straightway, soft seated quarter-turn valves when the valves are exposed to certain fire conditions defined in this standard. The procedures described in this standard are applied to all classes and sizes of such valves that are made of materials listed in ASME B16.34.

API 6FA

Specification for Fire Test for Valves, the standard covers the requirements for testing and evaluating the performance of API Spec 6A and Spec 6D valves when they are exposed to specifically defined fire conditions.

ZECO Valve is a API certified Valve Manufacturer, approved by API 6D, API 600, API 607 & API 6FA. If any inquiries, please contact us.

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So have you heard of PWHT? What’s PWHT?

Overview of Post Weld Heat Treatment (PWHT)

Welding is an essential part of operating and maintaining assets in the petroleum (upstream, midstream, downstream) and chemical processing industries. While it has many useful applications, the welding process can inadvertently weaken equipment by imparting residual stresses into a material, leading to reduced material properties.

In order to ensure the material strength of a part is retained after welding, a process known as Post Weld Heat Treatment (PWHT) is regularly performed. PWHT can be used to reduce residual stresses, as a method of hardness control, or even to enhance material strength.

If PWHT is performed incorrectly, or neglected altogether, residual stresses can combine with load stresses to exceed a material’s design limitations. This can lead to weld failures, higher cracking potential, and increased susceptibility to brittle fracture.

PWHT encompasses many different types of potential treatments:

Two of the most common types are post heating and stress relieving:

Post Heating:

Hydrogen induced cracking (HIC) often occurs when high levels of ambient hydrogen permeate into a material during welding. By heating the material after welding, it is possible to diffuse hydrogen from the welded area, thus preventing HIC. This process is known as post heating and should begin immediately after the weld is completed. Rather than being allowed to cool, the material needs to be heated to a certain temperature depending on the type and thickness of the material. It should be held at this temperature for a number of hours dependent on the thickness of the material.

Stress Relieving:

By the time it’s complete, the welding process can leave a large number of residual stresses in a material, which can lead to an increased potential for stress corrosion and hydrogen induced cracking. PWHT can be used to release these residual stresses and reduce this potential. This process involves heating the material to a specific temperature and then gradually cooling it.

Whether or not material should undergo PWHT depends on a number of factors, including things like its alloying system or whether it’s been subject to heat treatment previously. Certain materials can actually be damaged by PWHT, while others almost always require it.

In general, the higher the carbon content of a material, the more likely it needs PWHT after welding activities have been conducted. Similarly, the higher the alloy content and cross-sectional thickness, the more likely the material is to need PWHT.

When PWHT is required for Carbon Steel?

Post Weld Heat Treatment or PWHT of Carbon Steel must be performed after every welding in order to ensure the material strength of the part is retained. The exact criteria for PWHT of carbon steel are mentioned in the ASME BPVC code. PWHT ensures the reduction of residual stresses, controlling material hardness, and enhancement of mechanical strength.

Advantages of Post Weld Heat Treatment | Purpose of PWHT

If PWHT is neglected or performed incorrectly, the residual stresses can combine with service load stresses. The value may exceed a material’s design limitations leading to weld failures, higher cracking potential, and increased susceptibility to brittle fracture. Other benefits of PWHT are listed below:

• Improved metallurgical structure
• Improved ductility of the material
• Reduced risk of brittle fracture as ductility increases
• Relaxed thermal stress due to the redistribution of residual stresses.
• Tempered metal
• Removal of diffusible hydrogen which helps in preventing Hydrogen-Induced Cracking (HIC)

PWHT Method and Equipment

The local post-weld heat treatment of the welded joints on the pipes shall be carried out by the electric-resistance method after the completion of all welding or repairing operations.

•  The resistance heater is electrically and thermally self-insulated and is built to size for each individual pipe.
• The applied voltages across the coils are either 220 or 380 volts AC depending on the power requirements.
•  The power controlling panel of post-weld heat treatment is composed of:
• A temperature controller indicator and recorder of digital type.
• A potentiometer device that controls the percentage of power input to the coils.
• A switch On and Off indicator lights, input, and output terminals for power and thermocouple connection.
• Electrical power contactors of the proper rating.
• Each panel will supply a single heating station and therefore for each heating operation, one panel will be needed. Heating and cooling rates are adjusted by manual selection of the percentage of power input by means of potentiometers.

Requirements for Post Weld Heat Treatment or PWHT

Before applying for the detailed PWHT requirements and exemption in these paragraphs, satisfactory weld procedure qualifications of the welding procedures specification to be used shall be performed in accordance with all the essential variables of ASME SECTION IX including conditions of post-weld heat treatment and other restrictions listed below.

While carrying out local post-weld heat treatment, the technique of application of heat must ensure uniform temperature attainment at all points of the portion being heat treated. Care shall be taken to ensure that the width of the heated band on either side of the weld edge shall not be less than four (4) times pipe thickness or 2″ whichever is greater.

Throughout the cycle of post-weld heat treatment, the portion outside the heated band shall be suitably wrapped under insulation so as to avoid any harmful temperature gradient at the exposed surface of the pipe. For this purpose, the temperature at the exposed surface of the pipe should not be allowed to exceed 400°c.

The valves, instruments, and other special items with welding ends, shall be protected,   because of the risk of damage during post-weld heat treatment.

No welding shall be performed after PWHT.

Automatic temperature recorders that have been suitably calibrated shall be employed. The calibration chart of each recorder shall be submitted to the owner prior to starting the heat treatment operations and his approval shall be obtained. Recording equipment shall be calibrated at least once every 12 months. Also, the instrument equipment (potentiometer) which is used for calibration of recorders should be supported by a related certificate.

Preparation and Attachment of Thermocouple for PWHT

After performing visual inspection and removing surface defects and temporary tack welds (if any) an adequate number of thermocouples (based on the diameter of pipes) shall be attached to the pipe directly and equally spaced location along the periphery of the pipe joint. The minimum number of thermocouples attached per joint shall be 1 for up to 3″ diameter, 2 for up to 6″ diameter, and 3 for up to 10″and 4 up to 12″diameter and above. However, the required minimum number of thermocouples to be attached can be increased if it is found necessary.

The thermocouples shall be placed on the joint and in firm contact with the pipe as near as possible to the weld area. Thermocouples should be directly tack welded to the joint or heating band jointly provided that they have a tail of the same material and an approved filler wire or electrode not larger than 2.5 mm in diameter is used for tack welding.

In order to avoid incorrect temperature readings due to direct radiation to thermocouples, it shall be protected by ceramic fiber blanked or any other suitable insulation material.

Heating resistance elements shall be laid over the attached thermocouples throughout of heating band and shall be insulated as shown in Fig. 1 below.

Insulating materials shall be mineral wool/glass wool which can overcome the temperature employed. The minimum insulation thickness shall be 50 mm. To hold the insulation material in position wire mesh shall be wrapped around and tied or tied by other suitable means.

PWHT Temperature, Time Record      

The post-weld heat treatment temperature and time and its heating and cooling rates shall be recorded automatically and present the actual temperature of the weld area. Each thermocouple shall be connected to the controlling and recording instrument for each treated joint.

Heating, Holding, and Cooling in PWHT

The heating temperature above 300°c shall be recorded and the heating and cooling rate shall not be more than that specified in related WPS and standards but in no case, more than 200°c/hr, and the difference between the temperatures measured by various thermocouples shall be within the range specified.

The heat treatment socking temperature and holding time shall be as specified in related welding procedure specifications. For easy reference, the values for different types of steel are given in the following table.

The cooling down to 300°c shall be controlled cooling. Below that the cooling down to ambient temperature shall take place under insulation coating without controlling.

Few Important Notes related to PWHT

PWHT operation shall be performed only by trained personnel having a similar experience and approved by the owner.

During PWHT joints shall be protected from rain and wind by adequate rain cover and windshield.

Hardness tests after PWHT shall be performed to determine if heat treatment has been performed effectively. Normally for Carbon Steel, the maximum Brinnel Hardness is 200 HB.

Safety Precautions during PWHT

The following safety precautions shall be provided during PWHT:

Equipment and panels shall be properly earthed.

Electrical technicians shall work with proper safety wears such as rubber gloves, shoes, etc.

Only a certified electrician will work.

Joints under PWHT shall be well cordoned with red tape/red light and danger display to avoid unknown persons coming in contact with high voltage electrical connections.

An adequate platform shall be made for in situ joints to avoid fall of a person.

Based on the above, PWHT is the critical process needed for welded material, which should be paid enough attention to during production. 

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What is API 602 Standard?

This International Standard specifies the requirements for a series of compact steel gate, globe and check valves for petroleum and natural gas industry applications.

It is applicable to valves of

• nominal sizes DN 8, 10, 15, 20, 25, 32, 40, 50, 65, 80 and 100,
• corresponding to nominal pipe sizes NPS ¼, ⅜, ½, ¾, 1, 1¼, 1½, 2, 2½, 3 and 4,

and to pressure designations of Class 150, Class 300, Class 600, Class 800 and Class 1500.

Product Overview of API 602 Forged Valve

• Design Standards: API 602, ISO 15761, BS5351;
• End Connections: Butt Welding(BW)-ASME B16.25, Socket Welding(SW)-ASME B16.11, Threaded-ASME B1.20.1;
• Hydraulic and Air Test: API 598;
• Pressure & Ratings: ASME B16.34.

Design of API 602 Forged Valve

• Bolted bonnet, welded bonnet, pressure sealed bonnet;
• Fully guided one-piece solid wedge to reduce wear on seating surfaces;
• Effective back seating design and packing mechanism to ensure a tight stem seal; outside screw and yoke(OS&Y) with rising stem;
• Tee-head stem design to prevent the stem from becoming disengaged from the wedge while the valve is in service.
• Half grooved/ recessed body-bonnet joint design to accommodate spiral wound stainless steel gasket for tight body-bonnet sealing.
• Hard-faced surfaces of both seating rings and the wedge provide excellent wear resistance.

Trim Material Selection of API 602 Forged Valve

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What is a Stainless Steel Globe Valve?

Stainless steel globe valve is a type of globe valve that is made of stainless steel. This type of valve is meant for throttling, opening, or closing fluid flow. The stainless steel globe valve manufacturers mostly use stainless steel material to make the body, bonnet, disc, and stem. This helps to make the valve very strong and resistant to impact damage as well as able to withstand high pressure and high temperatures. Other parts of the stainless steel globe valves such as seats can be made of other materials such as plastic and or rubber. Stainless steel globe valves can be either soft seated or metallic seated valves. Metallic seated valves are the ones in which the seat is made of soft material like rubber and or plastic. Metallic seated stainless steel globe valves are the ones in which the seat is made of metallic material like stainless steel. Stainless steel globe valves use linear motion when closing or opening fluid flow. The closing member of a stainless steel globe valve is known as a disc. The disc fits on the seat to block fluid flow when the valve is closed. Stainless steel globe valve manufacturers design these valves to be either manual or automatic.

Structure of Stainless Steel Globe Valve

Stainless steel globe valves are heavy duty, outside screw & yoke type, bolted bonnet, rising stem, and hand wheel. Valves are highly efficient for services requiring frequent operation and throttling. The internal passage within the valve diverts flow through 90° changes of direction resulting in pressure drop and turbulence. The most advanced design features provide the ultimate in dependable, economic flow control. They are available in a wide range of sizes and weights. Globe valves are generally considered where moderate control or regulation of flow is required.

API 602 Forged Globe Valve

A comprehensive range of small forged gates, globe, check, angle, and bellows seal valves with unique design features.

Globe Valve Flow Direction

The most important thing to understand about globe valve direction flow is that they have specific flow directions. Depending on the application, a globe valve will have fluid flow above or below the disc.

Globe Valve Direction Flow Globe valves designed to have the pressure flowing under the disc are used in low-pressure and low-temperature applications such as general plumbing. This type of flow direction lets the disc rotate freely on the valve stem. This allows the disc to fit properly against the seat as the valve closes, which results in less seat leakage

Globe valves can also have pressure flow above the seat when applied as part of high-pressure and high-temperature systems. This type of flow direction helps to prevent the stem from contracting when it cools down and will keep the disc from lifting off the seat.

To determine the globe valve flow direction, simply look at its body. Here, you should find an arrow indicating the valve flow direction.

Features of Stainless Steel Globe Valve

1. The stainless steel globe valve structure is simpler than the gate valve, making it easier to manufacture and maintain.
2. The sealing surface is not easy to be worn and scratched, and the sealing property is good. There is no relative sliding between the valve flap and the sealing surface of the valve body when opening and closing, so it is not serious for the wear and scratch of the valve, with the features of good sealing performance, and long service life.
3. When opening and closing, the valve flap stroke is small, so the globe valve height is smaller than the gate valve, but the structure length is longer than the gate valve.
4. The opening and closing torque are a large, laborious, and long time.
5. Large fluid resistance. Because of the tortuous medium channel in the valve body, the fluid resistance is large, with huge power consumption.
6. Medium flow direction: When the nominal pressure is PN≤16MPa, the flow direction is usually downstream, and the medium flows upward from the valve flap. When the nominal pressure is PN≥20MPa, it is usually counterflow, the medium flows downward from above the valve flap, which increases the sealability. When in use, the medium can only flow in one direction and cannot change the flow direction.

Applications of Stainless Steel Globe Valve

Stainless Steel Globe valves are adequate for all service media. Valves are marked with flow direction since they are recommended to install with flow and pressure under the disc. It can also be installed in reverse conditions depending upon the conditions. The stainless steel globe Valve is generally faster to operate due to less travel. But requires much force to operate compared to Gate valves.

The stem axis of the stainless steel flange globe valve is perpendicular to the seat sealing surface. The valve stem opens or closes at a relatively short stroke, and the J41W globe valve has a very reliable shut-off action, making this valve suitable for use as a medium for shut-off, adjustment, and throttling. Once the J41W series stainless steel globe valve is open, there is no contact between its seat and the disc sealing surface, so its sealing surface is less mechanically worn. Since the valve seat and disc of most globe valves are easier to repair or replace the sealing element, it is not necessary to remove the entire valve from the pipe, which is ideal for the case where the valve and the line are welded together. The flow direction of the medium as it passes through such a valve will change, so the flow resistance of globe valves is higher than other valves.

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The post Stainless Steel Globe Valve Flow Direction – API 602 Forged Globe Valve appeared first on ZECO Valve.