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Q
Is it safe to use the SafeTap® tool in hazardous areas (zone 0)?

A
Yes – cold tapping is safe.

Cutting holes in tank roof, e.g in connection with preparations for tank cleaning operations, often pose great concern from tank owners and operators. However, with the Oreco cold tapping tool, the SafeTap®, holes in tank roof is cut in a safe and quick manner.

Cold tapping methods cool the equipment so that heat build-ups, fires and explosions are prevented. However, many conventional methods are slow, inconvenient and leave a desire for a safer method. For this purpose Oreco has developed the cold-tapping tool, the SafeTap®. Design features and procedures make the SafeTap considerably safer than most traditional cold tapping methods:

  • Before the SafeTap® is fixed to the roof, an inert tank atmosphere below 8% oxygen is produced as an extra precaution to eliminate the dangers of cutting in an explosive atmosphere.
  • There is no frictional heat build-up from mounting and operating the SafeTap®, as cutting oil added throughout this stage is cooling the equipment and prevents dangerous heat build-ups.
  • A gasket ensures that the operators are not exposed to hydrocarbon or H2s steam.
  • A powerful magnet placed on the bottom of the cutting head ensures that the cut-out roof plate does not fall in the tank, but is removed along with the cutting instrument – thereby eliminating the risk of the roof to to cause sparks.

Q
Will use of the SafeTap® tool have an impact on the strength of the tank roof?

A
In general the negative effect to the mechanical integrity of the tank roof, when circular perforations with the SafeTap® are made, is so minute that it in praxis can simply be regarded as negligible.

Test performed by independent notified body
Tests and reference tests performed with and without any load show that the maximum calculated stress levels never reached critical values. This is the conclusion that can be drawn from an analysis performed by FORCE Technology in Denmark, independent certifying body providing advanced technical consultancy on an international basis.

The analysis consists of tests measuring the stresses on a tank roof with circular perforations executed with the Oreco SafeTap®. The method used to calculate the stresses is the Finite Element Method (FEM) which is suitable for calculation of complex elasticity and structural analysis problems. The work considers stress analysis of a representative steel plate (S235) used as a sample and simulation of conditions of loads with and without circular perforations.

In the following some of the tests and the respective results obtained are described in order to give you insight into the test method. If you wish to see the full report, please contact Oreco.

The test results
One test determines the stresses in case of a worst case scenario on the tank roof section where the SafeTap has been used. Here the worst case scenario is an exaggerated load of 100 kg acting on the flanged steel trunk and applied as a compression load evenly distributed on the flange of the steel trunk. Furthermore, it was applied an extra load on account of equipment and personal of 300 kg which was distributed on the centre squared area of 1.0 mt. X 1.0 mt. The maximum stress around the circular perforation was found to be 21 MPa (see graph to the right) - a value far below the critical level of 235.


Graph showing test results

Conclusion of the test
Even in the test with the most extreme condition stimulated with exaggerated loads but perforation, the stress levels reach only 42 % of the critical yield stress level. It should be noted that additional findings in the test shows that, whenever some of the support legs are removed, there is a potential risk of reaching critical stress levels if the tank roof is overloaded (without circular perforations performed).

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