Navigating the complexities of engagement qualifications in single-use assemblies

Single-use assemblies are designed with many connection points, or engagements. This refers to the places where two components are assembled, such as tubing on a hose barb, or two sanitary flanges connected with a gasket and clamp. It’s important to ensure that these engagements can withstand the specifications for the intended application or process for which they will be used. Engagement qualification testing provides verification that all components of a single-use assembly are securely connected, preventing leaks, maintaining the integrity of the system and ensuring proper fluid flow throughout the process.

There are currently no industry standards for how engagement qualifications should be performed, which leaves room for interpretation on what factors to consider in testing. The 2022 ASME BPE Bioprocessing Equipment Standard requires that mechanical hose barb connections follow documented procedures using calibrated equipment and that mechanical hose barb connections are qualified by the assembler under an established testing program. The BPE standard also provides non-mandatory guidance on hose barb, tubing and retention device selection to ensure proper mechanical hose barb connections. The BPE is currently developing an information-sharing questionnaire around single-use mechanical hose barb connections, which will allow end users to ask the right questions to single-use integrators to help them assess the robustness of any performed engagement qualification testing on the supplier side.

Engagements Defined

An engagement is defined as the components being assembled (i.e., tubing to hose barb), how they are being connected (retention device type and quantity), the method of assembly (use of alcohol or tooling if applicable) and the installation parameters (tightening force). Given the number of combinations, there are many engagement options available for connecting the same two components. The table below summarizes these factors and their importance:

Engagement FactorsDescription

Refers to the two main components being connected. This would include tubing to hose barb, pinch clamp to tubing, or connecting a sanitary flange to another component with sanitary connection (e.g., filter, connector), utilizing a gasket and flange clamp.


Each component is composed of ports, which refer to the areas that another component could attach to. A port would be specific to a component vendor, material, and style/dimensions of the connection point, such that many components of the same combinations could be defined as having the same port. This could allow one engagement test to be performed and applied to many components with the proper rationale. For example, a Nordson 1/2 inch 600 series barb manufactured with Flint Hills P5M6K-080 resin would have the same port defined on a straight connector, reducer and tee connector.

Retention Device

The primary function is to prevent disengagement of tubing from the hose barb. Several options exist today, such as cable ties, Oetiker® clamps, and BarbLock® retainers. The type and specific item number of the retention device chosen, including the quantity used are important in defining the engagement parameters.

Method of Assembly and Closure Specifications

The tools and specifications of the tools being used are critical. The tools used in the installation of the retention device should be identified (cable tie gun, pneumatic Oetiker® tool) along with identification of the parameters of closure (closing force of cable tie or Oetiker® clamp) as this could impact the strength of the connection. Any tool used should be designed for repeatable closure performance.

The use of other tools is also important to consider, such as tubing expanders, or noting if alcohol is needed to smooth the assembly of tubing to hose barb.

To ensure alignment of sanitary flange connections, any tooling can be noted if required.

Engagement Testing Considerations

A documented procedure for connecting components along with controls to ensure repeatable connections in everyday manufacturing is needed, in addition to an established testing program to evaluate connection performance.

The actual testing of an engagement and the protocol used is important to define to ensure the integrity and functionality of the connection. As there is no industry standard for this testing, below are some key factors for consideration. Engagement qualification protocols and use conditions vary widely for any given pressure resistance claim which may or may not meet the application requirements.

Testing ConsiderationsDescription
Testing Conditions

This applies to various aspects:

  1. The number of assemblies that should be tested and any requirements to test components from different lots.
  2. The type of testing to perform (tensile (pull-off) test, burst pressure, leak testing)
  3. The leak testing method (dye penetration, bubble emission, pressure hold/decay, tracer gas) and test fluid (air vs water)
  4. Temperature of the fluid, and temperature the assemblies tested were exposed to.
  5. Testing under static conditions (no intentional movement of connection) or dynamic conditions (push/pull or movement of connections to simulate worst-case scenario) or a combination of both.
  6. Definitions on how testing is to be performed depending on the type (i.e., how to increase pressure, how long to hold pressure, test to failure or a defined value)
  7. Definition of acceptance criteria (maximum allowable leak limit, minimum pressure requirements or pull-off force, no visible leaks observed)
Sterilization Assemblies tested post-exposure to worst-case sterilization conditions can help ensure performance over the validated sterilization range. Risk assessments could be performed on testing done without sterilization treatment or other scenarios.
Aging It helps to understand the performance of the connection over time, post sterilization, and can help define the shelf life of a given assembly it is used on. Testing can be performed at t=0 to get a baseline result, as additional assemblies undergo accelerated or real-time aging to be tested later to confirm the results.
Visual Inspection Identification of when these should be performed, most commonly on all components prior to assembly, post-assembly to ensure the engagements were made properly, and after sterilization to note if any changes appear after this process prior to testing.
Risk Assessment As a database of testing results is compiled, trends may start to appear and help select the best type of retention device or tightening forces required for select application requirements depending on the connector, tubing material or size, or other factors. For high frequency engagements on established designs in use with limited qualification data, consideration to validate these by experience could be argued if there are no quality issues reported.

Single-Use Integrator Considerations

Single-use integrators may weigh several factors before deciding on what connection variables are preferred for design use and/or testing. The application needs are at the top of this list, but there are additional factors that could be considered:

Integrator ConsiderationsDescription
Application Requirements

This includes the pressure the connections will need to withstand in operation, operating temperature and if freeze/thaw is a factor, and the overall criticality of the application (such as if the assembly will be used for buffer vs. final filling as an example). Additionally, pressure pulsations, hydraulic shock and side forces on connections may pose challenges to engagement integrity.

Retention Device Selection

Historically, cable ties have been the industry standard, but other types of devices have entered the market and found more favorable in higher pressure applications (Oetiker® clamps and BarbLock® retainers, for example). Integrators may prefer one type over another due to frequency of use and familiarity, existing tooling already in manufacturing, or engagements already qualified for the connection/application using a particular type. Considerations on mixing retention device types within one design or if there is a preference for consistency may be needed. Some types of retention devices require many SKUs to cover common connection sizes, barb styles, or color options, which could increase the number of engagement qualifications required to establish a testing database.


Cost plays a role in the selection as different retention device types have different costs associated with them. This could apply to the retention device itself, the tooling required to make a consistent and secure connection on a repeatable basis, as well as operational factors such as the time required to complete one connection.

Operator Concerns

More manual connections may cause additional stress and strain on operators, especially for assemblies requiring many connections. These effects should be assessed when considering connection options.


It’s necessary for single-use suppliers to operate under standard operating conditions when performing mechanical hose barb connections and building assemblies to ensure repeatable results. There is a need to ensure that these connections do not leak and that they meet pressure requirements for the application. Having an established testing program for qualification of these connections reduces risk and provides evidence of connection integrity. Proper engagement qualification can contribute to the successful and consistent performance of single-use assemblies in various manufacturing and processing scenarios. In lieu of formal industry guidance, it’s important to review the factors related to the selection of retention device and assembly, along with the variables to be considered in selecting a testing approach.