Concrete pumping clamp failures

Issued: 12/05/2024
Last Updated: 14/05/2024

Purpose

The purpose of this safety alert is to highlight the hazards and risks associated with concrete pumping line clamps (also known as couplers or clips) and to provide guidance on ways to reduce the risk of failure. This includes the need for proper pre-pour planning to ensure the pumping equipment used is appropriate for the project and is used as per the manufacturer’s instructions.

The alert also highlights the safe use information that should be provided by clamp manufacturers, importers and suppliers to ensure clamps can be used safely, and guidance on information, instruction and training that should be provided to workers by persons with management and control of pumping operations.

Background

In four separate concrete pumping incidents, line clamps on satellite concrete placing booms have failed causing pressurised concrete to be released. In three of the incidents the clamp was also ejected across the site at high velocity. The four incidents involved clamps from two leading manufacturers of concrete pumping equipment (Figure 1).

While all four incidents occurred on satellite concrete placing booms, similar incidents could occur on truck-mounted concrete placing boom pumps.

_{Figure 1 - The clamps involved in the four recent incidents}

Concrete pumping line clamps are used to connect two sections of concrete pumping pipe together. There are several different types of clamps available: bolted clamps, quick release or snap clamps and high-pressure wedge-type clamps (refer Figure 2 for some examples). All four recent incidents involved quick release clamps, but similar incidents could occur with any type of clamp and the guidance in this alert is relevant to all types.

_{Figure 2 - Types of concrete pumping clamps or couplers}

_{Single bolt clamp}

_{Quick release clamp}

_{High-pressure wedge clamp}

Safety Issues

No injuries occurred as a result of these incidents, but each had the potential to cause serious or even fatal injuries if the high-pressure concrete or clamp had struck those in the vicinity, or if the clamp was ejected outside the site boundary and struck a member of the public or a vehicle.

Contributing factors

Although the recent incidents are still under investigation to determine the exact cause of the failures, concrete pump clamps can fail due to one or a combination of the following factors:

• Concrete pressure in the line exceeding the rated pressure of the clamp, especially at the lower rated boom end of the line.
• Line blockages due to internal fraying in end hoses, shards of steel from the pipeline or dried pieces of concrete in the mix.
• The use of excessively worn clamps that no longer provide the necessary clamping force.
• The use of damaged clamps.
• The use of clamps with concrete build-up on internal surfaces preventing proper engagement of pipe flanges.
• Hinge and lever pins coming out because the pin head is too worn.
• The use of poor quality clamps from questionable suppliers.
• Failure to insert the safety pin.
• Excessive wear on the pipe flanges at the clamp location.
• Couplers being used with incompatible flange types.
• Failure to install the rubber gasket in the clamp when it is installed.
• Failure to tighten bolted clamps to the specified torque.

Unfortunately, the pressure rating of a clamp is often less than the maximum possible concrete pressure that a pump can apply. This is especially the situation on large pumps used on high rise jobs, where the pump needs to be capable of pumping concrete at very high pressures.

It is important that the concrete line pressure does not exceed the maximum pressure rating of the component with the lowest pressure rating in the pumping line, taking into consideration the pressure loss throughout the line.

If the hydraulic pressure at the pump isn’t limited to a predetermined maximum allowable pressure, the concrete pressure will spike if a blockage occurs, and a clamp failure may occur.

A failure can also occur if the operator increases the pressure in an attempt to overcome a blockage.

Modern concrete mixes, which can incorporate high cement content, admixtures, recycled aggregates and quarry dust (instead of sand), can be significantly more difficult to pump despite having an appropriate slump. This necessitates dangerously high pumping pressures to achieve the appropriate flowrates.

WHSQ enquiries have also identified that concrete pump manufacturers, importers and suppliers provide limited information to end-users in relation to how to inspect clamps and when they need to be replaced. Concrete pump operators are subsequently not providing sufficient information, instruction and training to their workers on how often to inspect clamps and what to inspect for.

Action required

Pre-pour planning

Australian Standard AS2550.15:2019 recommends that the planning of concrete pumping requirements occurs as early as possible in a project and that the principal contractor, structural engineer, concrete supplier and concrete placing equipment operator are involved in the planning process. Where reasonably practicable, this planning process should involve consultation with the pump’s original equipment manufacturer as they have detailed knowledge of how to assess all relevant factors and determine the most appropriate equipment for the project.

The pre-planning process should enable the appropriate pumping equipment to be selected, the pumpability of the concrete mix to be determined and the maximum allowable pumping pressure for each stage of the project to be calculated.

The concrete pressure in a concrete pumping line drops as the concrete passes through the line due to friction losses and pressure (head) loss as the concrete travels upwards. The amount of pressure lost is dependent on the pumpability of the concrete, the diameter of the line, and the length and configuration of the line (vertical rise and fall, the number and angle of bends, the number of reducers etc). As such, for long pumping lines the pressure loss can be significant. On these projects it will be necessary to pump at a high pressure at the pump to achieve an appropriate flow rate at the placing boom.

However, the pressure in each section of the line should not be allowed to exceed the pressure rating of the weakest components in that respective section of the line. For example, the concrete pressure on a placing boom should not typically be allowed to exceed 85 bar, in accordance with the instructions of placing boom manufacturers.

Unfortunately, modern high strength concrete mixes can be significantly more difficult to pump than traditional mixes. A modern mix with high cement content, admixtures, or high fines content can be nearly twice as hard to pump as a traditional mix with an identical slump. Because of this, it is no longer possible to estimate the pumping pressure required for a given line length and configuration based on the concrete slump alone.

In these instances, it is strongly recommended that a concrete pumpability trial be conducted at the commencement of the project to enable the appropriate pumping equipment (pump, lines, and boom) to be selected, and the appropriate maximum allowable pump pressure at each stage of the project to be confirmed. This information should be supplied to the pump operator to enable them to limit the maximum pump pressure such that that the concrete pressure along the line does not exceed the pressure rating of the weakest component in the respective areas.

Project productivity gains provided by modern high strength, but low pumpability mixes should not compromise safety by increasing the risk of concrete pumping equipment failure.

Manufacturers, importers and suppliers of concrete pumping clamps

TheWork Health and Safety Act 2011 and Work Health and Safety Regulation 2011

set out various duties that apply to manufacturers, importers and suppliers of plant. These include a duty to ensure that plant is without risks to the health and safety of persons if the plant is used for the purpose for which it was designed or manufactured.

To help demonstrate compliance with this duty, manufacturers, importers and suppliers of concrete pumping clamps must ensure that clamps have been appropriately designed, manufactured and tested to ensure that they have the correct pressure rating (including any applicable factors of safety specified by relevant published technical standards). The pressure rating should then be clearly marked on the clamps.

Another duty that applies to manufacturers, importers and suppliers of plant is that they must give adequate information to those who they supply or provide the plant regarding any conditions necessary to ensure that the plant is without risks to health and safety.

To help demonstrate compliance with this duty, manufacturers, importers and suppliers of concrete pumping clamps should provide documented user instructions on when and how to inspect the clamps to ensure that they are safe for continued use. At a minimum, this information should include:

• How often to inspect the clamps (inspection intervals).
• What to inspect for (cracking, wear, damage, play in hinges/joints/handles etc).
• What critical measurements should be checked (with dimensional tolerances stated).
• What the pass/fail criteria are in relation to the above.
• Recommended maximum hours of use before replacement.
• Diagrams or photographs to assist with user understanding.

Persons in control of concrete pumping operations

Persons conducting a business or undertaking (PCBU) that are in control of concrete pumping operations have a duty to provide adequate information, training, instruction, or supervision to ensure their workers and other persons are protected from risks to their health and safety.

As such, PCBUs must provide workers who install, use, and maintain concrete pumps with adequate information and training on how to safely operate and maintain the concrete pumping equipment. This includes information and training in relation to how to safely use and maintain line clamps. At a minimum, this information and training should include:

• How to identify the pressure rating of each type of clamp in use, as some brands display the rating differently to others.
• Which clamp types are compatible with each type of pipe end fittings.
• When and how to conduct regular inspections and maintenance of the clamps in accordance with the manufacturer’s recommendations, the Concrete Pumping Code of Practice and AS2550.15.
• Clear instructions and measurable discard criteria so the workers are clear on when a clamp is not safe to use and should be replaced.
• How to perform a quick pre-use inspection of a clamp to ensure it is safe for use and free of damage, excessive wear, misalignment, worn pins, including pin ends that have worn away the retaining end.
• How to inspect the flanges of the pipes to be joined to ensure that the flanges are in suitable condition and will not cause a failure of the clamp.
• How to assess the alignment of the pipe sections to confirm that they are straight and do not place unintended stresses on the clamp that could lead to failure.
• How to safely fit the clamps, including always fitting the safety clip (note: these are not required with bolted clamps).
• Clearly specifying the calculated maximum allowable hydraulic and concrete line pressures for different jobs and/or phases of construction. E.g. the maximum allowable pressures will increase as a multi-story job increases in height, but the maximum concrete pressure at the placing boom should not exceed the rating of the weakest component (typically 85bar at the boom).
• How to limit the maximum hydraulic and concrete line pressure of the concrete pump accordingly.
• Special precautions to be taken where the pump’s maximum possible operating pressure exceeds the pressure rating of the clamp/line.
• Clear instructions on how to safely clear blockages without exceeding the pressure rating of the system (e.g. by using reverse strokes instead of increasing pressure).

Concrete pumping clamps are a relatively low-cost item and are easily replaced. A prudent approach would be for clamp inspections to err on the side of caution. If there is any doubt as to whether a clamp is safe for continued use or within acceptable wear limits it should be replaced.

To help prevent line blockages workers should also be trained in how to inspect end hoses to ensure they are safe for use and do not have excess wear or damage (e.g. exposed wires).

PCBUs in control of concrete pumping operations should also consider if it is reasonably practicable to use a screen over the pump hopper (e.g. 75x75mm mesh) during pumping operations to prevent the ingress of foreign objects and dried shards of concrete which can lead to blockages.

Notifiable incidents

Under work health and safety laws, you must notify WHSQ if any of the following happens at your place of work or is caused by the running of your business:

• the death of a person
• a serious injury or illness of a person
• a dangerous incident.

A dangerous incident is defined in work health and safety laws as an incident in a place of work that exposes a worker, or any other person, to a serious risk to their health or safety from an immediate or imminent exposure to:

• an uncontrolled escape, spillage or leakage of a substance.
• an uncontrolled escape of a pressurised substance.
• the fall or release from a height of any plant, substance or thing.
• the collapse, overturning, failure or malfunction of, or damage to, any plant that is required to be authorised for use in accordance with the regulations (inc. concrete placing booms).

As such, a concrete pumping line blow-out, including a clamp failure or breach of a pipe section, would generally need to be notified to WHSQ.

Read more information regarding notifiable incidents.