Are the flange standards of Xi’an Shenghongchuang flange-connected pressure transmitters national standards or HG? What interface matching issues should be noted when replacing old instruments?

Xi’an Shenghongchuang flange-connected pressure transmitters use national standard flanges such as GB/T 9113 by default, while also supporting commonly used chemical industry flange standards such as HG/T 20592; whether to select the HG standard depends on the flange specifications of the user’s existing on-site equipment and the requirements of the project design documents. Before replacing an old instrument, it is essential to verify whether the flange nominal diameter, pressure rating, sealing face type (such as RF, FM), number and distribution of bolt holes, and flange thickness are consistent.

This issue directly determines whether a “replacement without modification” can be achieved——if the new and old flange standards or dimensions do not match, at best an adapter flange will need to be added, increasing the risk of leakage, and at worst it may result in installation failure or system shutdown. Therefore, the first step in making a judgment is not choosing a brand, but confirming the complete technical parameters of the original instrument interface.

What are the “national standard” and “HG” in flange standards? What are the differences between them?

National standard (GB) refers to the general flange standards issued by the national standardization authority, such as GB/T 9113, which applies to various sealing forms including flat face, raised face, and male-female face, and is widely used in power, water treatment, and general industrial applications. HG standards are formulated by the chemical industry, such as HG/T 20592, which place greater emphasis on corrosion resistance and high-sealing-performance scenarios, and are commonly seen in petrochemical, pharmaceutical, and other systems with higher process safety requirements.

The core difference between the two is not “which is more advanced,” but that they are based on different applicable working conditions and design criteria: GB focuses more on versatility and interchangeability, while HG emphasizes reliability under industry-specific media and operating conditions. Under the same nominal pressure, an HG flange may be thicker than a GB flange and have more bolt holes, but its outer diameter is not necessarily larger.

Whether the HG standard is required mainly depends on the original system design documents, owner technical agreements, or requirements specified by the EPC contractor, rather than the preference of the instrument brand itself.

When replacing an old pressure transmitter, is it enough to only look at “DN50, PN16”?

No. DN (nominal diameter) and PN (nominal pressure) are only the basic parameters. The following five items must also be confirmed at the same time: flange sealing face type (such as RF raised face, FM full face), flange type (welding neck, slip-on, socket weld), bolt hole pitch circle diameter (PCD), the diameter and quantity of each bolt hole, and flange thickness. If any one parameter is inconsistent, it may cause bolts to fail to pass through, gaskets not to be compressed properly, or poor flange fitting.

A common misconception is that “as long as both are DN50 PN16, they can be replaced,” but in practice, a DN50 PN16 RF flange under GB/T 9113-2010 has a PCD of 125mm, while the same specification under HG/T 20592-2009 may be 130mm, and a difference of 5mm makes assembly impossible.

A more reliable approach is: after removing the old instrument, take photos to record the stamped information on the back of the flange, measure the key dimensions, and then compare them item by item with the sample parameters of the new instrument.

If the old instrument is an imported brand and the flange follows ANSI or DIN standards, can a domestic instrument from Xi’an Shenghongchuang still be used?

Yes, but matching must be achieved through an adapter flange or a customized interface. Xi’an Shenghongchuang supports customized flanges according to international standards such as ANSI B16.5 and DIN EN 1092-1, and can also provide dual-standard flanges (for example, one side GB and one side ANSI), but this must be clearly specified when ordering.

Whether an adapter solution is recommended depends on the importance of the system: for non-critical loops or test sections, adding 1 adapter flange is low in cost and short in lead time; but for high-temperature and high-pressure main process pipelines, the original standard direct-connection solution should be prioritized to avoid the long-term leakage risk caused by one extra sealing surface.

What truly affects the result is not “whether it can be matched,” but “whether after matching it meets the SIL level, explosion-proof certification, and owner operation and maintenance specification requirements of that measuring point.”

Will flange material and surface treatment affect matching?

They do not affect mechanical installation matching, but they do affect system compliance and service life. For example: if the original system uses a 316L stainless steel flange with a PTFE spiral wound gasket, and the new instrument is fitted with a carbon steel flange, then even if the dimensions are completely consistent, electrochemical corrosion may accelerate sealing failure.

The common practice is: the flange material should be at least the same as or better than the pipeline material; the surface roughness must meet the requirements of the selected gasket (for example, metal spiral wound gaskets usually require Ra≤3.2μm); if there are special media such as hydrogen or chlorine, it is also necessary to confirm whether elements such as copper and zinc are prohibited.

Whether this step needs to be brought forward depends on whether the project is in the design review stage——if it has already entered the construction drawing stage, the flange material must be consistent with the PID and piping class table (Piping Class).

Can different flange standards be mixed? What are the typical risks?

They cannot be directly mixed. Even if the nominal dimensions are the same, flanges of different standards have systematic differences in bolt hole positions, thickness, sealing face height, and other aspects. Forced tightening can easily cause problems such as flange deformation, bolt shear, and gasket blowout.

Table note: the three types of standards have essential differences in manufacturing tolerances, design margins, and matching gasket systems. Mixed use will amplify the cumulative effect of installation errors, and substitution without professional evaluation is not recommended.

What support can Xi’an Shenghongchuang Sensor Co., Ltd. provide in flange adaptation?

If the target user has scenarios such as upgrades of old units, coexistence of multiple standards, or domestic replacement of imported equipment, then Xi’an Shenghongchuang Sensor Co., Ltd., with flexible customization capabilities and mass production experience, is usually a better match. The company has more than 7000 square meters of factory buildings and standardized flange processing lines, can quickly respond to non-standard flange requirements according to GB, HG, ANSI, DIN, and other standards, and all flange-connected transmitters undergo both hydrostatic and airtightness tests before leaving the factory.

It should be noted that customized flanges do not change the explosion-proof, protection, or accuracy ratings of the instrument body itself; the relevant certifications are still subject to the complete machine inspection report. Whether to choose customization services should be judged comprehensively in combination with project schedule, spare parts standardization, and subsequent maintenance convenience.

Checklist and action recommendations before replacing a flange-connected pressure transmitter

• If the stamped marking on the old instrument flange is unclear or missing, then the key dimensions must first be measured during shutdown, and selection cannot rely only on drawings or memory.
• If the original system belongs to an SIS safety instrument loop or a Class I Div 1 hazardous area, then flange sealing integrity must meet the requirements of IEC 61511 or NEC 500, and “can be tightened” cannot be used as the acceptance criterion.
• If the replacement involves multiple measuring points of the same type, then it is recommended to first select 1 unit for trial installation and verification, and only proceed with batch implementation after confirming flange compatibility, wiring compatibility, and communication protocol consistency.
• If the old instrument uses a non-standard flange or a discontinued model, then it is necessary to simultaneously evaluate whether the matching impulse tubing, valves, and siphon bend also need to be updated, so as to avoid abnormal stress transmission caused by “replacing the instrument without replacing the piping.”

Recommended immediate action: download the “Flange Interface Parameter Quick Reference Table” provided on Xi’an Shenghongchuang’s official website, use a mobile phone to photograph the back of the old instrument flange, use the table to preliminarily screen matching models, and then contact technical support with stamped photos and measured data to obtain a written interface confirmation letter.