English
A flexible connector is part of the process boundary, not simply an accessory between two rigid pipes. During normal operation it can experience repeated flexing, vibration, pressure pulses, vacuum loading, thermal cycling and powder contact. During cleaning it may also be exposed to hot water, caustic solutions, acid rinses or steam. These conditions can occur simultaneously, which is why a material that performs well in one test condition may fail rapidly when several stresses are combined in production.
The most common selection mistake is to choose a material from one parameter only. A connector may have an attractive temperature rating but poor chemical resistance, excellent chemical resistance but excessive stiffness for a weighing application, or a suitable electrical resistance value but the wrong reinforcement for a metal-sensitive powder path. Wall thickness also cannot be used as a substitute for chemical compatibility. A thicker TPU wall may increase wear life, but it does not automatically make the polymer suitable for aggressive solvents or repeated high-temperature steam exposure.
For this reason, the first question should not be which material is the strongest. The correct question is which materials must be excluded by the actual process conditions. Once unsuitable grades have been eliminated, the remaining options can be compared by mechanical life, pressure capability, compliance documentation and total process cost.
The purchase price of a flexible connector is normally a small part of the operating cost of a powder-processing line. The larger financial exposure occurs when a failed connector causes contamination, cleanup, batch disposal, line stoppage, emergency maintenance or an investigation into the root cause of the failure. In food, pharmaceutical and battery-material production, a connector failure can therefore create a cost many times higher than the original component value.
A practical plant model should include the replacement component, the production downtime caused by the failure, the value of the affected batch and the labor and waste cost required to clean the area. The basic calculation is: Total Failure Cost = C_replacement + (T_downtime x R_plant) + C_batch_scrap + C_spill_cleanup. C_replacement is the replacement and emergency logistics cost, T_downtime is the production time lost in hours, R_plant is the fully loaded plant downtime rate in USD per hour, C_batch_scrap is the material or batch value written off, and C_spill_cleanup is the labor, disposal and sanitation cost associated with the event.
For example, assume a failed connector costs 350 USD to replace, the line is stopped for 1.5 hours, the fully loaded production downtime rate is 2500 USD per hour, the affected batch contains 2500 kg of product valued at 3.00 USD per kg, and the resulting cleanup requires 3 hours at 75 USD per hour. The replacement cost is 350 USD, the downtime cost is 3750 USD, the batch loss is 7500 USD and the cleanup cost is 225 USD. The modeled failure cost is therefore 11825 USD. This is an engineering planning example rather than a claim about a specific SOSHH customer, but it demonstrates why material selection should be based on total process exposure rather than component price alone.
| Material | Construction and Wall | Temperature and Cleaning | Chemical Compatibility | Pressure and Vacuum | Electrical Property | Do Not Use Under | Recommended Applications |
|---|---|---|---|---|---|---|---|
| PU10 | 1.0 mm polyether TPU; thicker configurations available | -30 to +110 deg C continuous; +120 deg C peak; 85 deg C CIP | Suitable for general powder duty; verify acids, concentrated caustic, ketones and aromatic solvents before use | +0.35 bar / -50 mbar standard configuration | Surface resistance >10^12 ohm; insulating | Repeated 2 to 5 percent NaOH at 85 deg C, repeated 121 to 134 deg C SIP, deep vacuum, long-term aggressive solvent exposure | General food, pharmaceutical and industrial powder transfer |
| PU15 | 1.5 mm polyether TPU | -30 to +110 deg C continuous; +120 deg C peak; 85 deg C CIP | Same base chemistry limitations as standard polyether TPU; thicker wall does not create chemical resistance | +0.70 bar / -120 mbar | Insulating | Aggressive solvents, repeated steam SIP, severe chemical exposure beyond qualification | Abrasive powders, minerals, resins and higher-wear powder transfer |
| PUAS | 1.0 mm static-dissipative polyether TPU | -30 to +110 deg C continuous; +120 deg C peak; 85 deg C CIP | Chemical compatibility follows the TPU formulation and must be checked separately | Standard pressure configuration; specify actual process pressure | 10^6 to 10^9 ohm/sq | Treating the connector itself as a complete ATEX approval, or using it for chemical duty outside the TPU envelope | Combustible dust, fine powders and applications requiring controlled electrostatic dissipation |
| PUHT | 1.0 mm high-temperature PU | -20 to +150 deg C continuous | Improved thermal envelope, but chemical compatibility remains application-specific | Standard configuration; verify actual pressure and vacuum | Insulating | Repeated steam SIP without specific qualification, or aggressive chemistry outside the material envelope | Hot powder and hot-air process lines up to the qualified temperature limit |
| PU10VR | 1.0 mm TPU with external coiled-wire reinforcement | -30 to +110 deg C continuous; +120 deg C peak; 85 deg C CIP | Same base TPU chemical limitations | +1.0 bar / -1000 mbar | Insulating | Applications where metallic reinforcement is prohibited or metal-sensitive inspection is required | Deep-vacuum powder conveying and pressure/vacuum cycling |
| PU10VRNM | 1.0 mm TPU with non-metallic POM reinforcement rings in external pockets | -30 to +110 deg C continuous; +120 deg C peak; 85 deg C CIP | Same base TPU chemical limitations | +1.0 bar / -500 mbar | Insulating | Vacuum beyond -500 mbar or applications where detector performance has not been validated on the finished assembly | Vacuum applications requiring non-metallic reinforcement |
| Pure PTFE | CNC-machined virgin PTFE; geometry-specific wall thickness | -70 to +260 deg C continuous; +280 deg C peak | High resistance to strong acids, caustic solutions and many aggressive solvents; verify exceptional conditions separately | Geometry-specific; engineered for demanding pressure and vacuum applications | Insulating | Conditions outside the selected PTFE design envelope | Pharmaceutical/API, aggressive chemistry, high-temperature powder service and repeated SIP |
| Platinum Silicone | Platinum-cured silicone; geometry-specific wall construction | -50 to +200 deg C; 121 deg C SIP reference | Good hygienic and thermal performance, but not the default for oils, fuels, strong solvents or severe chemical exposure | Low-duty and geometry-specific | Insulating | Oils, fuels, aggressive solvents and severe abrasive powder duty | Hot-air handling, drying, selected food/pharma applications and low-stiffness weighing |
Polyurethane chemistry must be considered by formulation rather than treated as one universal material. Polyester TPU is generally more susceptible to hydrolysis than polyether TPU because ester-containing structures are more vulnerable to hydrolytic degradation. Polyether TPU normally offers better hydrolysis resistance, which is why ether-based formulations are widely used where moisture exposure is important. However, higher hydrolysis resistance does not automatically establish suitability for repeated steam sterilization.
Repeated exposure to 121 or 134 deg C steam combines high temperature, moisture, pressure, thermal cycling and mechanical stress. These conditions can accelerate aging even when the polymer is described as hydrolysis-resistant. The correct engineering rule is therefore to qualify the exact material formulation and finished connector construction under the actual SIP cycle. A dry temperature rating is not the same as a steam-SIP qualification.
For repeated high-temperature SIP, Pure PTFE is the primary material direction in this selection guide. PTFE provides a substantially wider temperature and chemical-resistance envelope, making it the normal direction for demanding pharmaceutical and chemical process conditions.
A hot caustic cleaning cycle must be evaluated as a chemical exposure, not simply as a temperature condition. A typical 2 to 5 percent sodium hydroxide wash at 85 deg C creates a different polymer environment from dry powder transport at 85 deg C. Chemical diffusion, swelling, softening and mechanical degradation can accelerate when temperature and exposure time increase.
For standard PU10 and PU15, the +120 deg C peak figure does not establish long-term compatibility with 2 to 5 percent hot caustic at 85 deg C. The dedicated PU15CIP grade is the SOSHH selection for repeated hot caustic and acid cleaning at 85 deg C. The existing product data also include a 120-hour alternating acid and hot-alkali soak evaluation.
The final chemical compatibility decision should still consider concentration, exposure time, cycle frequency and the mechanical state of the connector during cleaning. A material that survives a static immersion test can still fail in service if the same chemical exposure occurs while the connector is repeatedly flexing.
Chemical attack can begin without an obvious crack. The polymer may first absorb the liquid, increase in volume, soften and lose mechanical strength. Under pressure or repeated movement, the swollen material can then develop local tears or permanent dimensional changes.
The specification should therefore state the exact chemical, concentration, temperature, exposure duration and cycle frequency. Standard TPU grades should not be selected for long-term exposure to aggressive ketones such as acetone and MEK or aromatic hydrocarbons such as toluene without specific qualification. Pure PTFE is normally the first material direction when aggressive solvent resistance is a controlling requirement.
Wear is strongly influenced by powder velocity, particle hardness, particle shape, concentration and wall movement. A laboratory abrasion value is therefore useful as a material-screening parameter, but it is not a direct prediction of service life.
SOSHH PU15 is specified at 39.0 mg DIN abrasion loss with a 1.5 mm wall, 40 MPa tensile strength and approximately 600 percent elongation at break. The value should be used for material comparison under the specified laboratory method, not as a universal prediction of production life.
For current documentation, the historical DIN 53516 reference should be retained only where it matches the original laboratory report. The current international standard is ISO 4649:2024.
Fine powders can generate static charge through repeated particle contact and friction against the process wall. PUAS uses a static-dissipative polyether TPU formulation with a surface resistance range of 10^6 to 10^9 ohm/sq. The electrical property is part of the connector design, but it does not replace grounding of metallic process equipment.
Where a hazardous area is involved, the engineering review should separately confirm the material electrical property, continuity through the installation, bonding of metallic equipment, the hazardous-area classification and the applicable conformity-assessment requirements.
A flexible connector can introduce mechanical force into a load-cell system when it is too stiff or when the installed length and movement are poorly matched to the application. This can appear as zero drift, apparent tare change, repeatability error or a slow change in measured mass as the equipment moves.
Low-force weighing designs should therefore be assessed using actual connector geometry and displacement. The relevant parameters include wall thickness, convolution geometry, installed length, spring rate, displacement and pressure differential. PU05WB is intended for this type of duty because the thin convoluted structure is designed to reduce parasitic reaction force.
Pressure and vacuum must be treated as separate engineering inputs. A higher-temperature grade does not automatically provide higher pressure capability, and a thicker wall does not automatically provide full vacuum resistance. Vacuum collapse is a structural problem involving wall geometry, reinforcement, installed gap and pressure differential.
The SOSHH reference envelopes are PU10 at +0.35 bar and -50 mbar, PU15 at +0.70 bar and -120 mbar, PU10VR at +1.0 bar and -1000 mbar, and PU10VRNM at +1.0 bar and -500 mbar. PU10VR uses external coiled-wire reinforcement and contains metallic reinforcement. PU10VRNM uses non-metallic POM reinforcement rings in external pockets and is intended for applications where metallic reinforcement is restricted.
Food-contact language must distinguish the regulatory framework from the actual finished-product evidence. FDA 21 CFR 177.2600 defines requirements for certain rubber articles intended for repeated food contact. European requirements should likewise distinguish the general framework of EC 1935/2004 from the plastic-material requirements of EU 10/2011.
SOSHH material documentation should identify the applicable regulation, the relevant material or finished construction, the supporting report or declaration and the scope of the evidence. Where the site uses FDA 21 CFR 177.2600, the applicable evidence reference should be shown with the relevant material documentation rather than presented as an unrestricted product-wide FDA certification.
First record the normal continuous temperature, the maximum process temperature, the peak exposure time and the cleaning or sterilization temperature. If the process remains within the standard TPU envelope, PU10, PU15 or PUAS can be considered based on the remaining conditions. If continuous temperature exceeds 110 deg C but remains within the PUHT envelope, PUHT may be considered. If the application reaches the PTFE operating range or requires repeated high-temperature steam exposure, evaluate Pure PTFE first.
Identify every chemical that contacts the flexible connector, including process chemicals, detergents, caustic washes, acid rinses, solvents and disinfectants. Record concentration, temperature, contact time and frequency. If the application uses repeated 2 to 5 percent caustic cleaning at 85 deg C, standard TPU should not be selected as the default. Use the dedicated PU15CIP direction or evaluate PTFE where the chemistry and temperature require a wider resistance envelope.
Record both positive and negative pressure in bar and mbar. Include pressure pulses and cycle frequency. PU10 and PU15 are intended for standard low-pressure powder duty, while PU10VR is the deep-vacuum direction to -1000 mbar and PU10VRNM is the non-metallic reinforcement direction to -500 mbar. The final rating must be checked against the actual connector diameter, installed length and temperature.
Determine whether metallic reinforcement is permitted in the product-contact path. PU10VR contains external coiled-wire reinforcement and should not be selected where metallic reinforcement is prohibited. PU10VRNM uses non-metallic POM reinforcement outside the product-contact path. The correct specification is no metal reinforcement in product path; validate with actual detector.
Determine whether the powder is combustible and whether the installation is located in a classified hazardous area. Where electrostatic dissipation is required, PUAS provides the specified static-dissipative property. The plant must still maintain correct bonding of metallic equipment and conduct its own hazardous-area assessment.
Record axial movement, lateral movement, vibration amplitude, movement frequency and any weighing accuracy requirement. In load-cell systems, the connector must not transmit excessive mechanical force into the weighing structure. PU05WB or an application-specific low-stiffness bellows construction should therefore be considered where reaction force is a critical parameter.
After the first six steps, eliminate every material that fails even one critical process requirement. The final material should be selected only from the remaining grades and then verified against the finished connector geometry. The objective is not to choose the material with the largest headline specification; it is to choose the material whose qualified operating envelope contains the actual production envelope.
For a standard milk-powder line operating at 25 deg C with dry powder, low pressure and no special static requirement, PU10 is normally the starting material. If the same line has a combustible-dust requirement, the selection moves to PUAS and the grounding arrangement must be reviewed separately.
For an abrasive mineral-powder line with repeated vibration and approximately +0.50 bar process pressure, PU15 is the more appropriate material direction because the 1.5 mm wall and 39.0 mg DIN abrasion value provide a larger mechanical wear margin than the standard 1.0 mm configuration.
For daily hot caustic and acid cleaning at 85 deg C, PU15CIP should be evaluated rather than assuming that the +120 deg C peak value of standard TPU establishes cleaning compatibility.
For a vacuum line operating at -1000 mbar where metallic reinforcement is permitted, PU10VR is the relevant vacuum direction. For a vacuum line operating at -500 mbar where metallic reinforcement is restricted, PU10VRNM is the relevant direction.
For pharmaceutical or chemical processing involving repeated 121 to 134 deg C steam exposure or aggressive solvents, Pure PTFE is the primary material direction because of its wider temperature and chemical-resistance envelope.
| Process Requirement | Primary SOSHH Direction |
|---|---|
| General food and powder transfer | PU10 |
| Abrasive powder and higher wear | PU15 |
| Static-dissipative powder handling | PUAS |
| Continuous process temperature above 110 deg C and up to 150 deg C | PUHT |
| Daily hot caustic or acid CIP at 85 deg C | PU15CIP |
| Deep vacuum to -1000 mbar | PU10VR |
| Vacuum to -500 mbar with non-metallic reinforcement | PU10VRNM |
| Aggressive chemistry and high-temperature SIP | Pure PTFE |
| Hot air, thermal service and low-stiffness applications | Platinum Silicone |
| Low-reaction-force weighing duty | PU05WB or application-specific low-stiffness bellows |
Material selection should be followed by qualification of the finished connector when the application is critical. Chemical qualification should use the actual chemical, concentration, temperature and exposure duration. Mechanical qualification should measure changes in dimensions, hardness, tensile strength and elongation where relevant. Dynamic qualification should reproduce the real displacement, frequency, pressure or vacuum and temperature. Containment testing should examine leakage, seam integrity, cuff retention and visible damage after cleaning. Weighing qualification should measure zero drift, repeatability and reaction force.
The purpose of qualification is not to create another laboratory number. It is to demonstrate that the finished connector continues to perform its intended function after being exposed to the same combination of process stresses that occur in production.
For a material-selection project, send the actual process conditions to the SOSHH engineering team. The most useful information is the process material name, chemical concentration where applicable, normal continuous temperature, maximum temperature, CIP temperature, SIP temperature if applicable, cleaning frequency, positive pressure, vacuum, dynamic movement or stroke, vibration frequency, metal-detector requirement, X-ray requirement, combustible-dust classification, food-contact requirement and any existing drawing or photograph of the installation.
The existing SOSHH engineering RFQ process remains the primary commercial path. Send the information to amin@soshh.com and attach an existing connector drawing, equipment drawing, dimensioned sketch or installation photograph whenever available. This allows the engineering team to review the material choice together with the connector geometry rather than treating the polymer selection as an isolated decision.
Where chemical compatibility is uncertain, an Engineering Material Sample Swatch Kit can be used for preliminary screening. The comparison set should contain representative samples of PU10, PU15, PUAS and Pure PTFE so that the customer can compare swelling, dimensional change, surface condition and relative stiffness after exposure to the process chemical.
Swatch testing is a screening step, not a production qualification. A material that passes a simple immersion test may still fail under combined temperature, pressure, flexing and chemical exposure. Critical applications should therefore be validated using the finished connector geometry and the real production duty.
For a material recommendation, dimensional review or custom connector quotation, email the process information to:
Please include the process material, chemical concentration, operating temperature, maximum temperature, cleaning method and temperature, positive pressure, vacuum, dynamic movement, metal-detection requirement, electrostatic requirement and existing connector or equipment drawing where available.
The existing SOSHH engineering workflow should remain unchanged. The purpose of this guide is to improve the quality of the information reaching the engineering team so that the material, reinforcement and connector geometry can be evaluated together.
Do not select a flexible connector because it is described as food-grade, chemical-resistant, high-temperature, anti-static or heavy-duty. Those descriptions are incomplete without process limits.
The correct material is the grade whose qualified operating envelope covers the complete production condition, including temperature, chemistry, pressure, vacuum, electrostatic duty, abrasion, dynamic movement and cleaning cycle.
When the application crosses more than one boundary, such as abrasive powder plus hot caustic cleaning, deep vacuum plus metal detection, or high temperature plus aggressive solvent exposure, the final material must be selected from the complete set of process conditions rather than from a single material property.
Engineering Material Selection and RFQ: amin@soshh.com
