Secondary containment storage bunds are a requirement for bulk storage of petroleum, petroleum products or other fuels in above-ground storage tanks (ASTs).
According to government guidance on COMAH establishments, ASTs holding flammable, highly flammable or extremely flammable substances should have additional secondary containment measures, such as:
• fire-resistant structural integrity, joints and pipework penetrations;
• a means of removing firewater from below the surface of the liquid in the bund (for hazardous substances which are not miscible with water and have a lower density than water).
Secondary containment is specified in COMAH Competent Authority (CA) Policy on containment of bulk hazardous liquids at COMAH establishments (‘Containment policy’) and associated guidance. These regulations implement most of the requirements of the pre-BREXIT EU Directive on the control of major-accident hazards involving dangerous substances (‘Seveso II directive’). This directive aimed to prevent major accidents involving dangerous substances, and limit the consequences to people and the environment.
Current requirements primarily arise from discussions about the Buncefield incident (please refer to the Buncefield Major Incident Investigation Board (BMIIB)) during the investigation following the Buncefield incident (see HSE Buncefield Major Incident Investigation Board – The Buncefield incident 11 December 2005: The final report of the Major Incident Investigation Board – Volume 1) (HSE BMIIB Final report Volume 1).
Recommendations were interpreted by the Buncefield Standards Task Group (BSTG) (please see the HSE Buncefield Standards Task Group – Final report: Safety and environmental standards for fuel storage sites) for more information and by the Process Safety Leadership Group (PSLG) (please see HSE Process Safety Leadership Group Final report: Safety and environmental standards for fuel storage sites).
Bunds can either be:
- manufactured as part of a tank system – tanks that are ‘pre-bunded’ by the manufacturer in this way are known as ‘integrally bunded’ tanks
- constructed from masonry or concrete
This article refers to bunds that have been constructed from masonry and concrete.
According to Oil Storage Regulations, you must ensure that:
- the bund is impermeable to oil and water – oil and water cannot pass through
- the base or walls of the bund do not have a pipe, valve or opening that allows the bund to be drained
- any fill pipe or draw-off pipe that passes through the bund base or wall is sealed to stop oil getting out of the bund
- the bund contains every part of the container and its associated equipment (such as valves) unless the oil being stored has a flash point of less than 32℃ (such as ethanol), in which case filters, sight gauges, valves and other equipment can sit outside the bund
The probability of a major leak from a well-designed and maintained storage
system is low. However, the consequences of an acid spill are potentially very serious and
measures to contain spillages or leaks from acid storage tanks should be provided.
Bunding is the usual method to contain spills or leaks from vessels.
Once the capacity of a bund has been calculated and a substrate selected, an assessment should be made to determine whether a lining system is needed.
Bunds constructed from masonry and concrete are likely to need a rendering or coating on the internal surfaces of the base and walls to make them impermeable.
Note: more detail on bund construction can be found in Containment systems for the prevention of pollution (C736F).
Selecting a bund lining requires careful consideration of several factors pertaining to the conditions that it will be exposed to.
The current good practice standard for the construction of reinforced concrete bunds is BS 8007:1987 Code of practice for the design of concrete structures for retaining aqueous liquids.
What is a Bund Lining?
Lining systems – internal coatings on the bund surface – act to protect the underlying substrate from external stressors (e.g. chemical attack, mild-moderate impact, frequent and sustained abrasion, temperature variation, etc.), thereby preventing a premature breach of substrate integrity.
In selecting a bund lining system, designers may consider:
- Performance
Normally testing is carried out in order to determine the suitability of a material of construction for handling a process fluid. However, testing can be used for different purposes. Typically this might be to justify a modified inspection frequency of equipment on an existing plant.
There are a variety of test methods available. Commonly test specimens consisting of small strips or ‘coupons’ of the material of interest are exposed to the process fluid. The weight loss of the test specimen over a time period is measured in order to determine the corrosion rate. Testing can be carried out on the plant, in the laboratory, or on a pilot plan depending on the situation.
Where laboratory testing is carried out using standard test methods there are difficulties in interpreting results and translating them into plant performance. Care is required to ensure that the test fluid is exactly the same as on the process plant. Discrepancies in test conditions such as trace impurities, dissolved gases, velocity, and turbulence can lead to erroneous results.
| Detail | Description |
|---|---|
| Performance | How does the lining system perform under intended conditions? For instance, does it remain chemically inert and impervious to nitric acid? What is there is a fire or temperatures are elevated, can the lining perform effectively until the situation has been adequately resolved? How resistant to abrasion is the lining? |
| Cost | What are the installation and material costs of installing the bund lining? |
| Size | Small-to-medium sized linings can be installed effectively by smaller teams and coverage rates are not as important. However, large-scale lining projects may require the selection of a more rugged lining system with quicker turnaround times at the expense of overall performance. |
| Installation time | How long does it take to install the lining and render it operational? If rapid turnaround times are required (particularly important for bund relining, repairs and refurbishments), how long will it take until the lining is operationally effective? |
| Lifetime | How long does the lining system remain operationally effective? |
| Ease of repair | In the event of any damage, can the lining be repaired? Are patch repairs over damaged areas suitable or is a full replacement required? |
Minimising downtime is an important feature, as is installing the bund lining in a reasonable timeframe. Certain lining systems may be better suited to small-to-medium sized areas, such as GRP linings.
Types of bund linings (SEPA COMAH)
Ultimately, different conditions and scales require different linings. Designers must ensure that the bund meets fundamental performance requirements
- Chemical resistance: the bund lining will need to be resistant and impermeable to the liquids stored.
| Chemical | Above Ground Storage Tank lining | Recommended Bund Lining | Notes |
|---|---|---|---|
| Chlorine | Wet chlorine gas corrodes mild steel. Chlorine gas handled at temperatures in excess of 200°C in carbon steel can result in chlorine / steel fires. | All chlorine storage tanks should be installed in a bund which is impervious to liquid chlorine. The bund should be capable of taking the contents of the largest storage tank with adequate freeboard and a sump. | Safety advice for bulk chlorine installations |
| Bromine | Lead used for steel storage vessels. Non-metallic linings including glass and certain fluorocarbon polymers, including PVDF and PTFE have replaced lead in most applications. | Epoxy is not recommended, whilst vinyl ester-based resin systems offer temperature-dependent resistance. | |
| Hydrochloric Acid | This acid is very corrosive towards most of the common metals and alloys. | The bund walls and floor should be constructed of materials resistant to the acid being stored. Acid resistant tiles are available and bricks and cement can be faced with acid resistant coatings. Coatings will require maintenance and regular renewal. | Bulk storage of acids |
| Nitric Acid | Vinyl ester is an effective lining system. See case study. | ||
| Sulphuric Acid | Corrosion protection of mild steel vessels occurs by the formation of an iron sulphate coating. | Vinyl ester is an effective lining system. | |
| Hydrofluoric Acid | Bulk storage of 70% acid or greater may be in mild steel or PVDF tanks. | GRP should never be used. | |
| Ammonia | Performance of most materials temperature dependent. Mild steel suitable at ambient temperature. Highly corrosive to copper and zinc. | ||
| Sodium hydroxide | Vinyl ester is an effective lining system. See case study. | ||
In regards to acid containment, for instance, the properties of the acid, its concentration, extent of impurities and storage temperature can all affect its interaction with a lining system.
Chemical resistance charts are available for epoxy resin, polyester, polyurethane and other resin-based lining systems. However, product manufacturers have designed more bespoke resin systems for different applications. Vinyl ester resin systems, for instance, have a range of sub-classes tailored to different applications, from flame retardancy to highly acidic chemicals – in addition to enhanced mechanical properties.
- Mechanical Properties: Abrasion resistance, Impact resistance
- Temperature stability
Vinyl ester bund linings demonstrate excellent resistance to diesel fuel, for instance, but not ethylene dichloride. Likewise, temperature is also a factor. The same linings are resistant to toluene under ambient conditions, but not at temperatures exceeding 71 oC. Given that toluene is a flammable liquid, such considerations should be made in the event of a fire.
The bulk storage of hazardous fuels and chemicals requires additional measures to prevent release in the event of a leak or other catatrophic event.
- Site-specific constraints
Fire resistance – particularly for fuel storage
Many secondary containment lining systems are expected to perform in the event of a fire. Systems like fibreglass can be engineered to incorporate flame retardant ingredients.
Bund liner quality is heavily dependent on the effectiveness and reliability of the installation process. Installation should be performed in accordance with manufacturer’s specification, which is likely to include:
| System | Advantages | Disadvantages | Fire Resistance | Cost |
|---|---|---|---|---|
| Fibreglass (Polyester) | – Easy application – Suited to small-to-medium areas. Hydrocarbon resistance. | Requires strong understanding of laminating techniques | Flame retardancy can be incorporated into the system. | Low |
| Fibreglass (Vinyl Ester) | Easy application. Suited to small-to-medium areas. Broad chemical resistance (acids, fuels, solvents, alkalis, etc.) | Flame retardancy can be incorporated into the system. | Low-Medium | |
| Polyurethane | Water resistant | Not resistant to oils and fuels. Requires protective layer | Very low. Burns readily if unprotected. | Medium |
| Poly-vinylchloride (PVC) | Resistant to oils and water | Not resistant to fuels. Requires protective layer. Potential hidden problems around seals and penetrations. Base ground to be prepared well (i.e., remove stones, requires layer of gravel and sand or geotextile before the liner. Requires specialist installer to weld joints. | Very Low. Burns readily if unprotected | Medium |
| Poly-ethylene (HDPE) | Resistant to water, hydrocarbons and most chemicals | Requires protective layer. Potential hidden problems around seals and penetrations. Base ground to be prepared well, ie remove stones, requires a layer of gravel and sand and geotextile before the liner. Requires specialist installer to weld joints. | Very Low. Burns readily if unprotected | Medium |
| Poly-propylene (PP) | Resistant to water and oils. Easier to lay than HDPE. | Limited resistant to fuels. Requires protective layer. Potential hidden problems around seals and penetrations. Base ground to be prepared well, ie remove stones, requires a layer of gravel and sand or geotextile before the liner. Requires specialist installer to weld joints. | Very Low. Burns readily if unprotected | Medium |
| Synthetic rubber and EPDM | Resistant to water | Not resistant to oils and fuels. Requires protective layer. | Very Low. Burns readily if unprotected | Medium |
- Installer:
- Training
by qualified personnel. This should Including sign-off,
- Experienced professionals
A demonstrated track record of successful bund lining installations should also be demosntrated. Many of these require field-acquired expertise in laminating and general resin application. Strandek has been installing fibreglass linings since 1976.
- Installation procedure:
Documenting the installation procedure is an important part in ensuring that the lining system is compliant with manufacturer’s specification. Key features to record are outlined in the table below.
Substrate
The condition of the substrate will dictate the performance of the lining. The lining itself is not intended to replace defective structural attributes of the substrate; instead, it should enhance existing properties. Key details in regard to the condition of the substrate are outlined in the table below.
| Detail | Description |
|---|---|
| Preparation work | Level (if any) of preparation work required to render the substrate surface amenable to lining |
| Visual inspection | Qualitative assessment of the overall condition of the substrate. Covers the extent of contamination (dust, grease, residual chemicals, dampness) as well as the identification of any sources of ingress. An assessment of the structural integrity is of the substrate is also recommended. |
| Moisture levels | Does the substrate have moisture levels below those deemed suitable for lining? Freshly laid concrete will have higher levels than existing concrete, for instance. |
| Roughness | Is the substrate in a condition which will allow the effective bonding of a liner? |
Materials
Ingredients used in the installation of these bund linings must match those outlined by the manufacturer. Ingredients must be within specification based upon pre-determined criteria and fully documented to ensure traceability.
| Material | What resin or reinforcement is being used? Materials must match up with those in specification. |
| Batch/Lot # | Manufacturer assigned |
| Expiry Date | Manufacturer assigned |
| Assigned Expiry Date | Assigned by installer upon opening. Usually 24-48 hours. |
Installation
The installation process itself is equally as important as the materials. Critical steps should be documented to ensure they are in line with specifications. The recording of installation procedures allows deviations to be identified in hindsight should any loss of integrity occur.
| Detail | Description |
|---|---|
| Time/date | Timestamp for completion of key steps |
| Performed by | Installer initials |
| Quantities | Quantities of ingredients utilised |
| Calculations | Quantitative methods used to determine quantities of ingredients to create specific mixtures |
| Cure times | Amount of time required for material to cure. |
| Atmospheric conditions | Refers to moisture levels (e.g rain or excessive humidity) as well as airbourne contaminants. Both will interfere with liner bonding. |
| Deviations | Procedures or calculations performed out of specification. |
At Strandek, we are often invited to demonstrate the installation process on site and to subject the lining system to customer testing. Whilst laboratory testing provides accurate chemical and thermal performance metrics, on-site testing enables a visual and practical assessment in the context of the process plant environment.
Steve Bowen, Managing Director, Strandek
- Evaluations should be documented and installed in accordance with an agreed design
- Project Installation Document
- Record installation in accordance with manufacturer’s guidance
- Deviations are expected to lead to increased risk of flaws and failures if unrecorded. Deviations should be recorded in the installation record
- Project Installation Document
- Installation involves:
- Pre-installation (preparation)
- Installation
- Post-installation management and monitoring
- Secondary containment features including lined bunds, should be added to site operating and management procedures
- Bunds should be protected via these procedures to minimise the risk of failure in the event of a breach
- Operating and management procedures should incorporate design and documentation of optimal performance appraisal for all bunded sites. Key features should cover:
- baseline establishment
Bund wall and floor construction and penetration joints should be leak-tight. Surfaces should be free from any cracks, discontinuities and joint failures that may allow relatively unhindered liquid transboundary migration. As a priority, existing bunds should be checked and any damage or disrepair, which may render the structure less than leak-tight, should be remedied.
Joints in concrete or masonry bund walls must be capable of resisting fire. Existing bunds should be modified to meet this requirement. In addition to repairing any defects in bund joints, steel plates should be fitted across the inner surface of bund joints, and/or fire-resistant sealants should be used to replace or augment non-fire-resistant materials.
- routine inspection and maintenance
- Insert the excel file…
- Bund integrity (leak-tightness) 159 Bund wall and floor construction and penetration joints should be leak-tight. Surfaces should be free from any cracks, discontinuities and joint failures that may allow relatively unhindered liquid trans-boundary migration. As a priority, existing bunds should be checked and any damage or disrepair, which may render the structure less than leak-tight, should be remedied.
- 160 Bund walls should be leak-tight. As a priority, existing bund walls should be checked and any damage or disrepair, which may render the wall less than leak-tight, should be remedied.
- HSE guidance on Material Requirements “Linings can deform or be damaged… The frequency of inspection can be amended once an inspection history has been built up and the condition of a piece of equipment can be reasonably predicted. The operator should demonstrate that it has inspection and maintenance programs in place for hazardous process equipment including lagged systems”
- testing and monitoring
- Weekly checks for signs of damage
- response procedures
- Arranging surveys
. A professional assessment is also recommended on an annual basis. Strandek routinely performs assessments of customer’s bund linings.
- Implementing repairs
The extent of
Concrete should be
- development of a documentation system
- Insert Word file as basis for this
- Refer to other documents
It may also be applicable to facilities that contain other products within the scope of the COMAH CA Containment policy.