D. JAIN, A. ASHESH and M. G. CHAUDHURY, KBR, Gurugram, India
Valves are essential components across industries such as oil and gas, power generation, water treatment and chemical processing. They regulate and/or isolate fluid flow, ensuring safe and efficient system operation. To guarantee reliability and performance, valves must conform to rigorous standards developed by organizations like the American Petroleum Institute (API), the American Society of Mechanical Engineers (ASME), the Manufacturers Standardization Society (MSS) and the International Organization for Standardization (ISO).
By understanding the nuances of standards such as API 600, API 602, API 623 and MSS-SP-144, engineers can make informed decisions that balance performance, compliance and cost. This article integrates case studies, selection flowcharts and tabular comparisons to support practical decision-making.
General valves standards. TABLE 1 details some essential general valve standards that support interchangeability and dimensional consistency across manufacturers.
GATE VALVES
Key standards. Gate valves are primarily used for on/off service. Various standards define their construction, performance and application scopes. TABLE 2 compares commonly referenced standards.
Comparative analysis. API standards like API 600 prioritize safety and reliability in demanding conditions, especially for oil and gas applications, by mandating features such as fire-safe construction and rigorous material specifications. In contrast, ASME B16.34 provides general design rules for pressure-containing components but refers testing requirements to standards like API 598, which is also cited in API 600.
While MSS SP-80 is often mentioned for cost-effective valve solutions, it primarily covers bronze valves for non-critical services, making it less comparable to API 600. A more appropriate comparison would be between API 600 and ASME B16.34, both of which apply to steel valves but differ in their emphasis on fire safety and corrosion allowances.
Commercially, gate valves built to API 600 tend to cost 20%–30% more than those conforming to ASME B16.34 or MSS SP-80 due to heavier construction and fire-testing protocols. This cost-performance trade-off supports the use of API 600 in hydrocarbon services, while ASME B16.34 or MSS SP-80 may be preferred in water systems or less severe applications.
Implications for selection. Gate valves can be manufactured to either ASME B16.34 or API 600, depending on service conditions and industry requirements. ASME B16.34 serves as a general-purpose standard for pressure-containing components across various industries, while API 600 is specifically tailored for the petroleum and natural gas sectors, emphasizing durability, corrosion resistance and fire-safe construction.
To illustrate the differences, consider a 6-in., Schedule 40, Class 600 gate valve:
ASME B16.34: Minimum wall thickness is calculated using Tables 3A or 3B. For a 6-in., Schedule 40 valve with an inside diameter of 154.06 mm, linear interpolation yields a required wall thickness of 13.18 mm.
API 603: Specifies a uniform wall thickness of 13.1 mm for 6-in., Class 600 valves, independent of pipe schedule.
API 600: Requires a significantly higher wall thickness of 19.1 mm, reflecting its focus on corrosion allowance and mechanical robustness.
Valves built to API 600 typically have thicker walls than those under ASME B16.34, enhancing resistance to corrosion, erosion and bonnet flexibility—especially under hydrostatic testing and high-pressure conditions. However, this also increases manufacturing costs. Engineers may prefer ASME B16.34-compliant valves in less severe services to reduce costs without compromising safety.
Stem diameter is another critical design factor. ASME B16.34 does not specify stem dimensions, leaving it to the engineer’s discretion. In contrast:
API 603: Requires a minimum stem diameter of 37.6 mm for a 6-in., Class 600 valve.
API 600: Specifies a slightly larger minimum stem diameter of 38.1 mm for the same size and class.
API 600 also mandates a split-wedge design, although this should be verified against the latest standard (e.g., Figure 2 of API 600), as it may allow flexible- or solid-wedge options. API 603 offers more design flexibility, permitting full-wedge, flexible-wedge and split-wedge configurations to optimize flow and reduce pressure drop.
Both API 600 and API 603 include backseat design provisions, enabling a metal-to-metal seal between the stem and bonnet when fully open. This feature prevents stem blowout and allows safe packing replacement under pressure, which is essential for live system maintenance.
Algorithm for selection. An algorithm for gate valve selection is shown in FIG. 1.
GLOBE VALVES
Key standards. Globe valves are commonly used for throttling and flow regulation.
Comparative analysis. API 602 focuses on compact, high-integrity globe valves for critical hydrocarbon services, featuring bellows stem seals to prevent fugitive emissions in small-bore applications (up to DN 100). In contrast, API 623 covers larger, heavy-duty steel globe valves (DN 50 and above) with stringent fugitive emissions requirements (API 624 tested), making it suitable for high-pressure refinery and petrochemical systems. While both API standards prioritize durability and leak prevention, MSS-SP-144 diverges by addressing pressure-seal bonnet designs for extreme pressures (up to CL4500) but does not inherently include fugitive emissions testing, instead referencing other standards for valves-specific requirements.
MSS SP-144 valves are primarily designed for high-pressure applications, particularly in power generation and steam systems, where pressure containment is the main concern rather than emissions control. Unlike API 602 and API 623 valves, which often incorporate bellows seals or meet fugitive emissions standards such as ISO 15848 or API 622, MSS SP-144 valves do not inherently comply with low-emissions requirements. While their pressure-seal bonnet design can help reduce potential leak paths and may incidentally minimize emissions, they are not guaranteed to meet regulatory thresholds unless specifically modified or tested for such compliance. Therefore, in applications where emissions are tightly regulated or critical to system performance, API-standard valves are generally preferred over MSS SP-144.
Implications for selection. Globe valves can be manufactured to API 602, API 623, B16.34 or MSS-SP-144, depending on application requirements, pressure conditions and fugitive emissions concerns. API 602 is optimized for compact, high-integrity applications in oil and gas, while API 623 covers larger, heavy-duty steel globe valves with strict emissions controls. MSS-SP-144, conversely, focuses on extreme-pressure applications with pressure-seal bonnets but does not inherently address fugitive emissions.
To illustrate the differences, consider DN 100 (NPS 4) SCH 40, Class 600 globe valves:
Wall thickness (ASME B16.34): The minimum wall thickness for the valves body and bonnet is determined using Table 3A or 3B. For a 4-in., SCH 40 valve with an inside diameter of 102.26 mm, linear interpolation yields a required wall thickness of 9.65 mm.
Wall thickness (API 602): The valve body minimum wall thickness can be determined using Table 5 of API 602. For 4-in. CL600 (irrespective of schedule), the wall thickness will be 11.9 mm.
Wall thickness (API 623): The valve body minimum wall thickness can be determined using Table 1 of API 623. For 4-in. CL600 (irrespective of schedule), the wall thickness will be 16 mm. Valves designed to API 623 typically feature greater wall thickness than those built to ASME B16.34 or API 602. This added thickness addresses corrosion, erosion and bonnet flexibility concerns, especially under hydrostatic testing and high-pressure conditions. However, it also results in higher manufacturing costs. Engineers may opt for ASME B16.34-compliant valves when service conditions allow, thereby reducing costs without compromising safety.
Similar to gate valves, stem diameter is another critical design factor for globe valves. ASME B16.34 does not specify stem dimensions, leaving it to engineer’s discretion. In contrast:
API 602: 4-in., Class 600 valves require a minimum stem diameter of 22 mm or 25 mm standard bore or full-bore valves, respectively.
API 623: Specifies a slightly larger minimum stem diameter of 32 mm for the same size and class.
API 602 and API 623 both enforce larger stem diameters than generic standards for better mechanical strength. API 623 requires heavy-wall stems to handle high-cycle operations. MSS-SP-144 stem sizing follows general pressure-seal design rules, often smaller than API valves unless specified otherwise.
Fugitive emissions and sealing technology:
API 602: Requires bellows stem seals as standard, ensuring no detectable leakage during pressure test which make these valves preferred for toxic or high-value fluid services.
API 623: Must comply with API 624 fugitive emissions testing (type testing required). Uses high-performance packing (e.g., graphite) but does not mandate bellows.
MSS-SP-144: No inherent fugitive emissions requirements—must be supplemented with API 624 or ISO 15848 if emissions control is needed.
API 602 valves are the most expensive for small sizes due to bellows seals and specialized compact designs. API 623 valves are costlier than standard ASME 16.34 globe valves due to heavier wall thickness but more economical than API 602 for larger sizes (DN 50+). MSS-SP-144 valves are competitive for high-pressure steam or power plants where emissions are not critical.
API 602 and API 623 use bolted bonnets for ease of maintenance. MSS-SP-144 uses a pressure-seal bonnet, which is self-energizing at high pressures but less accessible for repair.
Engineers must balance cost, emissions compliance, pressure rating and maintenance needs when selecting among these standards. API valves offer higher assurance for critical services, while MSS-SP-144 provides a robust solution for extreme-pressure applications where emissions are secondary.
An algorithm for globe valve selection is shown in FIG. 2.
CHECK VALVES
Key standards. Check valves are used to permit one-way flow and prevent backflow. The standards for check valves, shown in TABLE 3, differ by construction types, service severity and material types.
Comparative analysis. API standards for check valves cater to distinct industrial needs, with API 594 serving as a broad-spectrum standard for flanged, wafer and butt-weld check valves in oil and gas applications. In contrast, API 602 targets compact, high-integrity valves (≤ DN 100) for critical hydrocarbon services, emphasizing fugitive emissions control through bellows seals or tight packing. API 6D specializes in pipeline valves (up to DN 1500), including axial flow and full-bore designs, with optional fire-safe and emissions-compliant features.
MSS-SP-144 diverges by focusing on pressure-seal bonnet check valves for extreme pressures (CL600–CL4500), ideal for power plants but lacking emissions requirements, while API standards prioritize durability and safety in harsh environments.
Implications for selection. The selection of an appropriate check valves standard requires careful consideration of several critical factors, including size limitations, pressure class requirements, fluid service compatibility and regulatory compliance mandates. For hydrocarbon pipeline applications, API 6D represents the mandatory specification, particularly when axial flow or full-bore designs are required, while API 594 serves as the preferred choice for general refinery applications utilizing swing or dual-plate configurations.
In applications demanding compact, high-pressure solutions such as chemical injection systems, API 602 emerges as the optimal selection due to its incorporation of bellows seals and pressure ratings up to CL1500. Power generation facilities requiring extreme pressure valves up to CL4500 will find MSS-SP-144 to be the most suitable standard, though it is important to note that supplementary emissions testing to API 624 must be specified separately when fugitive emissions control is required.
The cost-to-performance ratio presents significant variations across these standards. API 602 and API 6D valves typically command a 20%–40% price premium over API 594 equivalents, reflecting their specialized materials and enhanced testing protocols. MSS-SP-144 valves provide a cost-efficient solution for high-pressure steam applications while sacrificing integrated emissions controls.
An algorithm for check valve selection is shown in FIG. 3.
Case studies for all types of valves based on experience are discussed below:
Case 1: In a refinery project requiring 6-in. Class 600 gate valves for high-temperature hydrocarbon service, API 600 was selected over ASME B16.34. The increased wall thickness, corrosion allowance and defined stem dimensions provided enhanced safety and performance under severe conditions.When it comes to fugitive emissions, API 6D references API 624, which focuses on methane leakage testing, while ISO 14313 aligns with ISO 15848, covering a broader range of gases and offering more comprehensive environmental compliance. In Arctic and environmentally sensitive projects, dual compliance with both standards is often adopted to meet stringent safety and sustainability requirements (TABLE 4).In summary, API 6D is preferred where enhanced safety margins are critical, whereas ISO 14313 is advantageous for projects requiring international compatibility and broader emissions testing.
Case 2: In a detailed evaluation conducted during a UOP-led project, the use of dual-plate wafer check valves in hydrocarbon service was ultimately disqualified due to performance and reliability concerns. While these valves are favored for their compact design and cost-effectiveness, the study revealed that they exhibited inconsistent sealing performance under fluctuating flow conditions typical of hydrocarbon processing systems. Additionally, the spring-assisted plates were found to be susceptible to vibration-induced fatigue and premature wear, particularly in high-temperature and high-pressure environments. These issues raised concerns about backflow prevention reliability, a critical safety requirement in hydrocarbon applications. As a result, the engineering team concluded that swing check valves or axial flow check valves—despite their larger footprint—offered superior durability and sealing integrity, making them more suitable for critical hydrocarbon service lines.
Case 3: For 6-in., Schedule 40, Class 600 globe valves, ASME B16.34 specifies the minimum body wall thickness using Table 3A or 3B, which, based on an inside diameter of approximately 154.06 mm, results in a value of around 13.18 mm through linear interpolation. In comparison, API 623, which adopts API 600 requirements, mandates a uniform minimum wall thickness of 19.1 mm for this valve’s size and class, regardless of schedule. This added thickness enhances resistance to corrosion, erosion and mechanical stress. While ASME B16.34 does not prescribe minimum stem diameters—leaving sizing to the manufacturer based on design and material strength—API 623 specifies a minimum stem diameter of 48 mm (Table 3) compared to API 600's 38.1 mm. The larger stem in API 623 reflects its high-integrity design intent, ensuring better torque transmission and sealing reliability under high-pressure or steam service. Conversely, B16.34 valves with smaller stems may be prone to wire drawing, seat erosion or leakage in such conditions. Additionally, API 623 accounts for the restrictive flow path of globe valves by defining minimum seat diameters (Table 4), maintaining a balance between shutoff performance and flow efficiency. In a relevant case study, a 6-in., Class 600 globe valve used in a power plant steam header—handling clean, non-corrosive steam—was specified to ASME B16.34, leading to cost savings due to lighter construction and adequate performance. However, in more demanding services, the higher robustness of API 623-compliant valves may be essential to ensure safe and reliable operation over the valves’ life cycle.
Case 4: In a subsea crude oil transfer pipeline application requiring DN 300, Class 900 check valves, several critical factors influenced the selection process. The need for full-bore design to minimize pressure drop eliminated conventional swing check valves from consideration, while the subsea environment demanded exceptional corrosion resistance and reliability. After evaluating alternatives, an API 6D-compliant axial flow check valve constructed from Alloy 625 (UNS N06625) was selected. This choice satisfied all key requirements, including fire-safe construction per API 607/6FA, fugitive emissions compliance per API 624 and the necessary durability for high-cycle operation. While this solution carried a 30% cost premium compared to standard swing check valves, the long-term performance benefits and risk mitigation justified the investment, particularly given the critical nature of subsea infrastructure and the prohibitive costs of subsea maintenance.
Case 5: A high-pressure amine injection system requiring DN 50, Class 1500 check valves presented unique challenges, particularly regarding fugitive emissions control and space constraints. The compact nature of the skid-mounted system necessitated valves with minimal face-to-face dimensions, while the toxic nature of the service fluid mandated zero fugitive emissions. After thorough evaluation, an API 602 piston-type check valves with integrated bellow seal was selected over alternative ball-type designs, which were deemed susceptible to sticking in amine service. This solution provided the required CL1500 pressure rating in a compact footprint while completely eliminating stem leakage pathways. The 40% cost premium over standard check valves was offset by eliminating potential environmental and safety incidents, demonstrating how specialized valves features can provide operational and financial benefits in critical applications.
Case 6: A power plant's high-pressure steam line application requiring DN 200, Class 2500 check valves highlighted the importance of matching valves specifications to service conditions. While API standards were considered, the MSS-SP-144 pressure-seal swing check valves emerged as the optimal solution, offering a self-energizing bonnet design specifically engineered for extreme-pressure steam service. The absence of fugitive emissions requirements in this application made the additional testing and features of API-compliant valves unnecessary, allowing for a 20% cost savings compared to API 623 alternatives. This case demonstrates how proper standard selection can optimize both performance and cost when application requirements are thoroughly understood and matched to valves capabilities.
There are areas of harmonization and gaps among standards. For example, API 6D aligns closely with ISO 14313 for ball valves, promoting international standardization. However, MSS SP-70, which covers gray iron valves, lacks weldability guidelines, unlike API standards that provide clear instructions for welded construction.
Takeaways. This paper has examined key valves design standards—API 600, API 602, API 603, API 623, API 594, API 6D, ASME B16.34 and others—highlighting their scope, applications and design philosophies. Through selected comparisons (such as wall thickness, stem diameters and valve types), it is evident that:
API standards generally emphasize performance, integrity and long-term reliability in critical applications.
ASME B16.34 allows greater flexibility and cost efficiency for non-corrosive, less severe conditions.
Valves specifications can significantly impact procurement cost and service performance. Engineers should assess service conditions carefully before defaulting to heavier, costlier specifications.
The central inference is that a functionally similar valves may differ significantly in construction, durability and cost depending on the chosen standard. Understanding these nuances enables more informed, application-specific decision-making—striking the right balance between reliability and economics. HP
LITERATURE CITED
American Petroleum Institute (API) 600, “Bolted bonnet steel gate valves for petroleum and natural gas industries,” 11th Ed., 2021.
American Petroleum Institute (API) 602, “Compact steel gate valves—Flanged, threaded, welding, and extended body ends,” 2020.
American Petroleum Institute (API) 603, “Corrosion-resistant, bolted bonnet gate valves—Flanged and butt-welding ends, 2021.
American Petroleum Institute (API) 623, “Steel globe valves—Flanged and butt-welding ends, bolted bonnets,” 2021.
American Petroleum Institute (API) 594, “Check valves: Flanged, lug, wafer, and butt-welding end,” 2020.
American Petroleum Institute (API) 6D, “Specification for pipeline and piping valves, 2021.
American Petroleum Institute (API) 624, “Type testing of rising stem valves equipped with graphite packing for fugitive emissions,” 2021.
American Society of Mechanical Engineers (ASME) B16.34, “Valves—Flanged, threaded, and welding end,” 2020.
Manufacturers Standardization Society (MSS) SP-80, “Bronze Gate, globe, angle, and check valves,” 2013.
Manufacturers Standardization Society (MSS) SP-144, “Pressure seal bonnet valves,”2016.
International Organization for Standardization (ISO), “Petroleum and natural gas industries—Pipeline transportation systems—Pipeline valves,” 2007.
International Organization for Standardization (ISO) 15848-1, “Measurement, test and qualification procedures for fugitive emissions of valves—Part 1: Classification system and qualification procedures for type testing of valves,” 2015.
European Committee for Standardization (CEN) 12334, “Industrial valves—Cast iron check valves,” 2001.
European Committee for Standardization (CEN) 13709, “Industrial valves—Steel globe and globe stop and check valves,” 2003.
American Petroleum Institute (API) 607 / API 6FA, “Fire test for quarter-turn valves and valves equipped with non-metallic seats,” 2020.
Dinesh Jain works as a Piping Engineer at the KBR India Technology Centre, Gurgaon. He has more than 15 yrs of experience in piping stress and piping materials for the petrochemicals industries. Prior to joining KBR, he was associated with Technip Energies, Petrofac and Samsung Engineering.
Avijit Ashesh works as a Piping Engineer at the KBR India Technology Centre, Gurgaon. He has more than 17 yrs of experience in the design, engineering and troubleshooting of piping systems for the fertilizer, refining and petrochemical industries. Prior to joining KBR, he was associated with PDIL, Samsung Engineering and Fluor Corp.
Mrinmoy Ghosh Choudhury is an Engineering Professional with extensive experience in process plant engineering from concept to commissioning with special emphasis on piping and plant engineering whether concept layout, stress and support or materials. He has been involved in numerous problem-solving challenges related to plant startups like vibration, rotary equipment alignment, piping/equipment system failures, etc. He has contributed numerous papers to reputed engineering journals like hydrocarbon processing, etc. In his professional life, he has been involved with KBR India Technology Centre, Reliance Engineering, Toyo Engineering India, Chemtex Engineering India, Engineers India Ltd. and DCPL.