Introduction                                                                                                                                                                             

 

As a core connecting component in industrial fluid systems, double‑card‑type fittings are widely used in applications such as atmospheric‑pressure instrumentation, ultra‑high‑pressure valves and fittings, test connectors and hoses, closed‑loop sampling systems, and process valve assemblies. The quality of their installation directly affects the system’s sealing performance, stability, and safety. Whether it is instrument line connections under atmospheric pressure, medium transport under ultra‑high pressure, or precision connections in testing systems, any oversight during installation can lead to fitting leaks, loosening, or even failure—resulting in production interruptions, media loss, and safety hazards.

Leveraging years of experience in the production and application of double‑card‑type fittings—covering both atmospheric and ultra‑high‑pressure specifications—and drawing on real‑world installation case studies, JW‑LOK has systematically identified the six most common issues encountered during installation. The company then conducts an in-depth analysis of the root causes and potential hazards of these problems and provides practical, implementable, standardized solutions.

 

Common Installation Issues and Solutions                                                                                                                              

 

1. Mixing materials and specifications creates inherent risks.

Root cause:

On-site spare parts management is not standardized, and operators lack sufficient understanding of material compatibility and specification differentiation, mistakenly believing that… “Sizes that are similar can be used interchangeably.” In particular, some metric and imperial dimensions are nearly identical—for example, 1/4-inch and 6-mm ferrules. If these are mixed together, they can be very difficult to distinguish.

Therefore, couplings of different specifications should be stored separately. Additionally, during installation, carefully verify that the correct specifications are being used to prevent the aforementioned issues from occurring.

Core Hazard:

• Mixing different materials can easily lead to galvanic corrosion—when two dissimilar metals come into contact in an electrolyte environment, a potential difference arises, which, over prolonged operation, corrodes the joints and steel pipes, compromising their sealing performance and mechanical strength.

• A mismatch in hardness can prevent the ferrule from properly gripping the steel tube, resulting in an unreliable seal.

• Mixing different specifications can lead to abnormal assembly stresses and uneven fit clearances between fittings and steel pipes, making them highly susceptible to loosening and leakage under pressure pulsation or vibration conditions.

JW-LOK Solution:

• Prior to installation, rigorously verify the coupling’s specifications, material, and operating conditions to ensure that the coupling and steel pipe are either of the same material or an equivalent material combination. Strictly differentiate between metric and imperial dimensions to prevent any cross‑use.

• Our company’s double‑card sleeve fittings are manufactured using differentiated materials to suit various operating conditions, including atmospheric and ultra‑high pressure applications. We also strictly distinguish between metric and imperial specifications, with clear markings on each specification and material type to prevent the risk of misapplication.

 

2. Improper pretreatment of steel pipes compromises the sealing interface.

Frequently Asked Questions:

• The steel pipe surface exhibits defects such as scratches, dents, and depressions;

• After pipe end cutting, burrs were not removed, leaving sharp edges;

• The pipe end is not perpendicular to the axis, and the ovality exceeds the allowable tolerance;

• Chamfer is too deep or not chamfered at all.

Core Hazard:

• Surface defects on steel pipes can compromise the sealing interface between the ferrule and the pipe, creating microscopic gaps that lead to fluid leakage.

• Burrs or sharp edges at the pipe end can damage the ferrule’s cutting edge, compromising proper deformation and crimping.

• If the pipe end is not perpendicular or if its ovality exceeds the allowable limit, the ferrule will experience uneven stress, preventing effective sealing. Under ultra‑high‑pressure conditions, this can easily lead to joint failure.

JW-LOK Solution:

• During transportation and storage, ensure proper protective measures are taken to prevent surface damage.

• Prior to installation, rigorously inspect the external condition of steel pipes; any sections with defects must be cut out and reprocessed.

• After cutting, steel pipes must be deburred on both the inner and outer surfaces using specialized deburring tools. The chamfer depth at the pipe ends shall be no greater than half the pipe wall thickness, ensuring that the pipe ends are smooth and free of sharp edges.

 

3. The steel pipe was not fully inserted into the joint body, resulting in failure of the sealing engagement.

Root cause:

• Lack of specialized, high‑precision verification tools; non‑standard operating procedures; or inadequate removal of burrs from pipe ends can cause the steel pipe to become jammed between the front and rear ferrules, preventing full insertion.

• Some personnel tightened the nuts prematurely before inserting the steel pipe, causing the ferrule’s inner diameter to shrink and preventing the pipe from being fully seated.

Core Hazard:

• If the steel tube is not fully inserted, the rear ferrule will be too close to the tube end, preventing proper crimping of the steel tube.

• Under conditions of vibration and pressure pulsation, steel pipes are prone to loosening and detachment; under ultra‑high‑pressure conditions, they may even cause the medium to jet out, leading to safety accidents.

• At the same time, it can cause deformation of the ferrule, compromising its sealing performance and reducing the service life of the fitting under repeated assembly and disassembly.

JW-LOK Solution:

• Before tightening the nut, ensure that the steel pipe is fully inserted into the fitting body and abuts against the internal shoulder.

• The depth‑marking tool provided by our company can be used to mark the steel pipe, ensuring that the insertion depth meets the required specifications.

• It is strictly prohibited to tighten the nut in advance when no tube has been inserted.

• If the steel pipe cannot be fully inserted, inspect the pipe end for burrs and check whether the ferrule is deformed; address any issues promptly before proceeding with assembly.

 

4. Incorrect installation of the ferrule results in loss of sealing performance.

Common specific issues include:

• Front and rear ferrules installed in misaligned positions;

• The front or rear ferrule is installed in the wrong orientation;

• The rear ferrule is missing or improperly installed;

• The ferrule was not properly seated during assembly, resulting in misalignment.

Core Hazard:

• Incorrect installation of the ferrule can prevent it from deforming properly: the front ferrule fails to establish an effective sealing interface with the steel tube and the fitting body, while the rear ferrule cannot securely grip the steel tube, leading to leakage and loosening of the fitting.

• Under ultra-high-pressure operating conditions, misalignment of the ferrule may result in uneven stress distribution, leading to ferrule fracture and medium leakage.

JW-LOK Solution:

• Before installation, inspect the ferrule for integrity and ensure that both the front and rear ferrules are present and undamaged.

• Assemble strictly in accordance with the product markings to ensure correct orientation and proper positioning.

• During assembly, avoid loosening or removing the ferrule nut arbitrarily to prevent the ferrule from shifting.

If you are unsure whether the assembly is correct, please refer to the assembly diagram provided by our company or contact us.

 

5. Improper tightening torque can lead to seal failure or component damage.

Root cause:

There is a lack of specialized torque tools, and operators lack a clear understanding of the appropriate tightening torque, making it difficult to determine the correct torque requirements for joints of different specifications and operating conditions.

Core Hazard:

• Insufficient tightening can result in poor contact between the ferrule and the steel tube as well as the fitting body, leading to inadequate sealing pressure. This may cause fluid leakage during system operation, particularly when using test‑grade fittings, thereby compromising test accuracy.

• Over-tightening can deform the ferrule, steel tubing, or the fitting body, damage the sealing surfaces, reduce the fitting’s service life under repeated disassembly and reassembly, and may even strip the threads, rendering subsequent removal and maintenance impossible.

 

JW-LOK Solution:

• Use our company’s matching torque tools or gap gauges to assess the tightening condition—when the gap gauge cannot be inserted into the space between the nut and the fitting body, it indicates that the joint has been adequately tightened.

• Operate strictly in accordance with the tightening torque specifications provided by our company; for fittings of different sizes and materials, adhere to the corresponding requirements, and avoid relying on experience alone.

• When reassembling the joint, refer to the marking positions from the initial installation to avoid over-tightening.

 

6. No leak‑tightness test was performed after installation, leaving a potential leakage risk.

Root cause:

• Operators harbor a sense of complacency, believing that “as long as assembly follows the specifications, there will be no issues,” and thus neglect the inspection stage.

• Lack of professional testing tools and awareness, with an unclear understanding of testing procedures and standards.

Core Hazard:

• Minor leakage hazards can gradually escalate, leading to media loss and environmental pollution.

• Leakage of toxic, hazardous, flammable, or explosive media can lead to safety accidents;

• Under ultra-high-pressure operating conditions, even minor leaks can be exacerbated by pressure surges, leading to equipment damage and production disruptions.

JW-LOK Solution:

• After installation is complete, a leak test must be performed. Under low-pressure conditions, apply soapy water to the joint connections and observe for the formation of bubbles.

• For high-pressure, precision‑grade applications—such as test fittings and closed‑system sampling—we use our proprietary leak‑testing equipment to conduct pressure tests in accordance with industry standards, ensuring zero leakage before commissioning.

• Establish inspection records and retain installation and testing data to facilitate subsequent traceability.

 

JW-LOK We offer a range of ferrule‑tube installation tools specifically designed for double‑ferrule fittings, including pipe benders, pre‑assembly tools, tube cutters, and deburring tools, helping customers streamline the installation process. The ferrule pre‑assembly tool simplifies the installation of double‑ferrule fittings in tight spaces and significantly speeds up the installation of large volumes of such fittings.

 

Conclusion                                                                                                                                                                                

The installation quality of double‑card‑type fittings directly affects the safe and stable operation of industrial fluid systems; even seemingly minor installation oversights can give rise to serious hazards. Most of the common issues mentioned above stem from improper procedures, insufficient understanding, or a lack of appropriate tools, rather than any inherent product‑quality defects.

 

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