What are the special requirements for emergency shut-off valves?

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This post was last edited by shiwendong on 2018-5-30 23:25. What are the special requirements for emergency shut-off valves? Tracing the term further back, the definition of an Emergency Block Valve (EBV) in “Refinery Control Valves” (API RP 553-1998) is as follows: 7.2.1 Emergency Block Valves. Emergency block valves are designed to address hazardous incidents; they are used for emergency isolation purposes and are intended to prevent the uncontrolled release of flammable or toxic materials. Such valves must be of fire-safe rating if they are located within a fire zone. These valves can be classified into Types A, B, C, and D. It is clear that only valves situated in fire zones are subject to these special fire-safe requirements. However, in the design documents of China’s petrochemical industry, no such requirements can be found at present. Similarly, API RP 553 also defines the fire zone. 7.2.2 Determination of Fire Zone: This is the area that is unsafe to enter during an emergency. The distances mentioned are given as examples only; actual distances should be referred to in the plant’s standards. The area in question is considered to be within a radius of at least 25 feet around the source of the leak. However, despite clear definitions provided in the API specifications, in the current domestic context, there is no connection between emergency shut-off valves and fire zones. The understanding of the term “emergency shut-off valve” remains at a conceptual level; it is seen as something similar to a simple message conveying the importance of having such valves in place to ensure they function during emergencies – that’s all. Therefore, it is necessary to make a straightforward distinction between fire-resistant emergency shut-off valves and non-fire-resistant emergency shut-off valves. For fire protection emergency shut-off valves, see the analysis below. As defined in API RP553 7.2.1, emergency isolation valves (EBVs) are generally classified into the following four types: (1) Type A – manually operated valves installed on the equipment; such valves are installed in locations where a leak may occur but no fire will break out ； These are generally process valves. (2) Type B manually operated valve installed on process pipelines ； Such valves are installed at a location 25 feet (7.6 m) away from the point of fire or leakage, and their size is not larger than 8 inches, with a pressure rating not exceeding ASME CLASS300. These are generally process valves. (3) Type C power-operated valve installed on process pipelines ； Such valves are installed at a distance of 25 feet (7.6 m) from the point of fire or leakage, have a diameter of more than 8 inches, a height of no more than 15 feet, and meet pressure ratings exceeding ASME CLASS300. (4) Type D power-operated valves, which can be closed using buttons installed on-site and in the control room. There are not many restrictions on the installation location of such valves, but the control buttons should be installed outside the fire hazard area, at a distance of 40 feet (12.2 m) from the point of fire or leakage. Actuators, control cables, power pipelines, etc., located within the Fire Zone are designed to be fire-resistant, or such that their operation will not be impaired in case of a fire; the supports for these pipes and wiring are also designed to be fire-resistant. Based on practical engineering experience, the emergency isolation valves EBV that we commonly encounter generally meet the requirements of type D. Regarding the selection of actuators, there are electric, pneumatic, hydraulic, etc.; the following discussion will take the pneumatic actuator as an example. According to the definition of control valves given by the International Electrotechnical Commission (IEC), a control valve consists of an actuator and a valve body component. The \"Code for Selection and Design of Automation Instruments in Petrochemical Industries\" (SH/T3005-2016) also provides descriptions regarding fire protection for both the actuator components and the valve body parts. It mentions on multiple occasions valves that are fire-safe and meet the API 607 or API 6FA standards, as well as the requirement to install fire protection covers that comply with the UL1709 standard. So what are these 3 criteria? II. Fire resistance of valve body components / Fire-test API607 is titled \"Fire test for valves that can rotate 1/4 turn and valves with non-metallic seats.\" It is generally applied to valves that can only rotate 90° (such as ball valves, plug valves, butterfly valves, etc.), and it relates to the fire resistance test of valves with soft seats; it cannot be used for valves with metal seals. API6FA is the standard specification for fire resistance testing of valves; it is a general standard that can be applied to hard-sealed valves. At the same time, it should be noted that the test procedures specified in these two standards do not require fire resistance tests for electric, pneumatic, and hydraulic actuators; API 607 explicitly states that these three types of actuators are not covered by this standard. Regarding the often-mentioned fire protection requirements or fire protection functions, \"fire resistance\" is a more accurate term. The fire resistance of a valve is defined as its ability to continue functioning properly in a high-temperature flame; it is one of the important indicators for assessing a valve’s safety performance. The fire resistance test of a valve is the only method for determining its fire resistance. It should be noted that the fire-resistant property of a valve does not mean that it will not leak at all in high-temperature flames, nor that it will remain leak-free throughout ； Rather, it refers to the amount of leakage that a valve is allowed to have under high-temperature flames for a certain period of time (usually 30 minutes). The main leakage criteria and operational requirements for valve fire resistance testing include leakage during the burning period, leakage outside the burning period, low-pressure tests after cooling, and operational tests. Therefore, SH/T3005-2016 specifies essential fire-safe requirements for the valve body, internal valve components, valve cover, and packing. In engineering practice, if the relevant discipline upstream does not specify any fire protection requirements, how should one determine whether the valve needs to be fire-safe? Generally, in the specifications regarding material grades, safety requirements such as fire resistance, anti-static properties, and prevention of spillage are indicated for process valves; in such cases, it can be assumed that the valve needs to be fire-safe. There are not only API standards for fire resistance testing, but also other **standards from various organizations; these need to be distinguished from one another in engineering applications (primarily API in the United States and BS/ISO in Europe). III. Fire protection requirements for actuators – Fire shields. The two API fire-type-testing standards do not specify any requirements regarding pneumatic, electric, or hydraulic actuators; for details, see the standards (API 607: “It does not cover the testing requirements for valve actuators other than manually operated gear boxes or similar mechanisms when these form part of the normal valve assembly. Other types of valve actuators (e.g., electrical, pneumatic, or hydraulic) may need special protection to operate in the environment considered in this valve test, and the fire testing of such actuators is outside the scope of this international Standard”). However, API 6Fa does not mention actuators at all, nor do the testing procedures address them. Standard API 607 specifies the fire test requirements for valve body components; it does not apply to electric, pneumatic, or hydraulic actuators. SH/T3005-2016 requires the use of fire shields, and such shields must have a type approval certificate in accordance with UL1709 issued by a classification society, ensuring that the temperature inside the shield remains within the operating temperature range of the actuator even 30 minutes after a fire occurs. The standard full name is as follows: UL1709: Rapid Rise Fire Tests of Protection Materials for Structural Steel. Section 4 – Engineering Practices – Taking Pneumatic Valves as an Example. If it is not a fire-resistant emergency shut-off valve (which can be considered to be outside the Fire Zone), then ordinary on/off valves should be selected for engineering purposes to meet the process requirements; or, depending on actual needs, API fire protection requirements must also be satisfied. When the valve is a fire-proof emergency shut-off valve (which can be considered to be located in a Fire Zone), there are two possible scenarios: Scenario 1: The process requirements dictate that the valve must act immediately in the event of a fire. In the event of a fire, the process requirements dictate that materials be cut off to create a barrier, which allows for effective control of the fire at the earliest possible moment. This in turn creates favorable conditions for subsequent firefighting efforts, helping to prevent serious safety accidents. Under these requirements, selecting valves that meet the fire resistance standards specified by the API will satisfy the fire safety requirements (with the exception of the actuators). No requirement can be imposed on the executing agency. After all, what is needed at this time is for the valve to operate as required by the process specifications (in terms of timing), in order to cut off the material and provide isolation. As for the operating time of the valves, it is generally determined by the process requirements (taking into account issues such as water hammer and steam hammer; the operation may also need to be slow. If the operation time is too long, the fire protection requirements for the actuator must also be considered, although such requirements are very rare in these devices). In addition, a spring-return type actuator in fail-safe position (general FC) mode can be preferred ； Alternatively, a fuse can be installed on the actuator ； Alternatively, a sun-resistant, fusible material such as polyethylene pipe can be used for the section of the gas supply pipeline near the valve, etc., to meet the fail-safe position (typically FC) requirements in case of a fire. These are all setup requirements considered from the perspective of intrinsic safety. Of course, there is also a view that the actuator should also be designed with fire protection (fire shields) to prevent loss of control over the valve position due to damage to the actuator caused by a fire. A fuse is installed on the actuator. . . Case 2: In processes where it is required that the valve open at a certain time during a fire, the valve operation needs to be delayed. However, in the event of a fire, there are often process requirements that dictate continuous operation despite the fire situation. At this time, while isolating equipment with a high fire risk, it is necessary to ensure that no more serious process safety incidents occur. The aforementioned method (where the valve body components meet API fire protection requirements) cannot ensure the requirement for continuous operation of the valve. For example, the joints of the air supply pipelines (Tube pipes) may deform due to high temperatures, resulting in significant leakage of instrument air and making it impossible to operate the valves. In such cases, the fire protection design of the pneumatic actuation mechanism and its associated air supply pipelines must be given careful consideration. SH/T3005-2016 requires the installation of fire protection covers to meet the requirement of UL1709, namely a fire resistance time of not less than 30 minutes at 1093°C. In addition, fire-resistant cables, gas supply pipelines, and fireproof covering for cable trays must also be used to meet the requirements of the overall fire protection design. V. Summary: A brief overview; the installation of emergency shut-off valves is determined by the process engineering team in accordance with standards or industry practices ； 1) There are no fire protection requirements; the engineering design is carried out by using conventional valves and switches, or API fire protection requirements are met as needed ； 2) Fire protection requirements apply; the valve must operate promptly as needed. Some of its components meet API fire protection standards. Depending on the actual situation, fusible plugs or fusible gas supply lines can be used, or additional measures can be taken to ensure fire protection for the actuator as required ； 3) Fire protection requirements are applicable; there is a need for delayed operation, and both the valve body components and the actuator as a whole must meet fire protection standards, in compliance with API+UL 1709. Additionally, the fire protection requirements for piping, wiring, and cable trays must also be taken into account. Note: The actual requirements here refer to taking into account the relative positions of the valve piping and fire protection areas, as well as other practical considerations, etc. 6. Explanation: Any standard has associated system-related issues. For example, the API 6Fa standard specifies that it applies to valve products in accordance with API 6D (which references ASME B16.34). But do these two API standards also apply to valves designed and manufactured in accordance with ASME B16.34 as mentioned in SH/T 3005? SH/T 3005-2016 also does not provide any provisions regarding this, but the client and the project contractor can make such requests. Special attention should be paid during the project to the applicability of relevant standards as well as to any special requirements beyond those set by the contractor or the client, in order to avoid over-design. 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