Leak sealing repair clamps
UKOOA for dissemination to End Users Suppliers of Leak Sealing Repair Clamps
1. Repair clamps are sometimes used as a temporary repair to seal small leaks in pipework. The purpose of this note is to highlight a recent incident which has shown that such clamping repairs may be inadequate without recourse to additional measures to give the pipework sufficient structural strength. Such failures obviously have the potential to cause fatal injury.
2. A recent incident occurred where degradation of a pipe within a leak sealing repair clamp resulted in a structural failure of the pipe, leading to the pipe and its contents being ejected from the clamp. The pipe failed due to insufficient thickness to resist the normal axial load due to pressure and other forces (e.g. thermal expansion). The repair clamp only sealed the leak but did not provide sufficient axial strengthening of the pipe.
3. The incident was an example of failure to fully assess the conditions in which the clamp was being used. This can be caused by:
- An inadequate initial assessment of the nature and location of the defect to which the clamp is being applied.
- Failure to establish accurately the operating conditions to which the clamp will be subjected. This should include pipe contents, pressure, temperature, pipe size and combinations thereof.
- Failure to remove the repair clamp within suitable timescales where the enclosed pipework is subject to ongoing degradation, including failure to appreciate that a need to re-inject the clamp may be an indicator of significant further degradation of the pipe material.
- Failure to take into account the geometry of the pipework being repaired (eg pipe ovality) which could affect the performance of the repair clamp (or of a separate restraint such as a gripper clamp if provided).
Actions Required By Duty Holders
4. For safety critical piping systems the repair philosophy should
- Replace like-for-like.
- Temporary repair until replacement can be carried out.
- Permanent repair only where replacement is not practical.
5. This approach is in line with the principles of prevention as outlined in the Guidance to the Management of Health and Safety at Work Regulations 1999, SI no. 3242 - in particular the principle of "control risks at source, rather than taking palliative measures" is relevant.
6. The use of leak sealing clamps should be adequately controlled by appropriate procedures. Users of leak sealing repair clamps should carry out the following steps prior to the use of such a clamp:
- An assessment of the nature and extent of the defect being considered for repair.
- A full assessment of the operating conditions to which the clamp will be subjected. This should include pipe contents, pressure, temperature, pipe size and combinations thereof.
- An assessment of the timescale for which the clamp is required to be in operation.
7. If a leak sealing repair clamp is considered suitable following these assessments then this information should be communicated to the clamp supplier.
8. It should be ensured that all pipes enclosed by repair clamps are provided with structural restraint unless a suitable and sufficient assessment (which should take into account the potential failings in paragraph 3 above) shows this not to be necessary. It is particularly important to consider the ability of the remaining wall thickness to accommodate the imposed axial loadings/stresses. In situations where the continuation of internal metal loss cannot be prevented it will be necessary to consider the suitability of the repair component to accommodate these loading/stresses should this continuing metal loss affect the pipe's ability to carry these loading/stresses. Additional measures to provide sufficient structural restraint for axial loads should be available from clamp suppliers.
9. Great caution should be taken where there is a need to re-inject existing clamps and structural restraint has not been provided. A suitable and sufficient risk assessment of the conditions in which the clamp has been employed should be carried out (which should take into account the potential failings in paragraph 3 above).
10. Users of existing leak sealing repair clamps which have not been provided with full structural restraint should carry out a suitable and sufficient risk assessment of the conditions in which the clamp has been employed (which should include consideration of the conditions in paragraph 3 above). Note this may result in it being necessary to remove some existing clamps from service.
11. Leak sealing repair clamps are temporary repairs. Such temporary repairs should be removed and replaced with a suitable permanent repair at the next available maintenance opportunity. Temporary repairs may remain in place for a longer period of time only if approved and documented by a person competent to do so.
Relevant Legal Requirements
12. The main legal requirements include:
- Health and Safety at Work etc Act 1974.
- Provision and use of Work Equipment Regulations 1998.
- Management of Health and Safety at Work Regulations 1999.
- Pressure Systems Safety Regulations 2000 (where applicable).
13. These are legal duties on both the owner/operator of the plant and on those who carry out the repair and/or modification.