Tapping on tank roof - a safety concern

The mere idea of cutting in the EEx Zone 0 area on a tank floating roof raises concerns of explosion and fire risks. Yet there are a number of potential benefits to be gained from the ability to cold tap on the tank roof while in service. Oreco has solved this problem with its introduction of the SafeTap® cold tapping tool.

The subject of tapping holes into the roof of an external floating roof tank while the tank is in service is frequently a very sensitive issue in the eyes of both tank farm managers and tank maintenance personnel.

For some, the mere idea of cutting in an EEx Zone 0 area conjures visions of explosions, fires and other catastrophic situations. This is sufficient to evoke the firm response of “no, we do not allow tapping on the tank roof during service, and that is that!” 

Why tap holes on tank roofs?
There can be some substantial benefits associated with the ability to create additional openings on the tank roof during service. For example, tapping openings just prior to tank cleaning using the Oreco automated tank cleaning systems allows the optimal placement of the appropriate number of Oreco Single Nozzle Sweeper (SNS)® tank cleaning nozzles on the tank roof, thereby assuring the best possible cleaning result.

Moreover, the fitting of the new holes with approved roof nozzles and blind flanges once the tank is cleaned allows the use of the new flanged holes for subsequent tank cleanings, thereby saving time in future mobilisations.

Conventional cold tapping method
Conventional cold tapping method involves drilling holes in the tank roof while using large quantities of cooling water to prevent fire or explosion. A series of adjacent holes are drilled in a circular pattern, creating the hole. Any remaining area is then cut using a metal saw. The workers must work in waterproof coveralls and supplied breathing air, which can be uncomfortable and hinder movement. A safety watch must also be present to observe the work.

All personnel working with supplied breathing air may only work for a maximum of 30 minutes per hour. Consequently, this procedure is very slow and tedious, and experience shows that a maximum of 3 holes can be created in a day’s work.

The safe solution – the SafeTap®
In light of the difficulties associated with conventional cold tapping, a better method is desirable. The ideal solution to this situation would be an effective, fast and above all completely safe method for cold tapping holes in the tank roof while the tank is in service.

Oreco has developed and now offers just such a solution: the SafeTap® cold tapping tool. The SafeTap tool enables the cold tapping of an appropriately-size opening in the tank roof in a matter of minutes.

The tool consists of two main parts: a trunk which is placed on the tank roof, and a cutting instrument which is used to perform the actual tap. The SafeTap® can be used to cut holes in steel plates of up to 6 mm in thickness. Once the hole is cut, the cutting instrument is removed and a tank cleaning nozzle is installed through the newly created hole resting on the trunk.

Once the tank cleaning procedure is complete and the tank is ventilated and declared ready for hot work. The trunk on the tank roof is removed and, hot-tapping of a flanged roof nozzle is performed in full compliance with the prevailing standards and regulations for welded steel tanks (example: API 650, Section 3.8.5, “Roof Nozzles”). This new nozzle is then fitted with a blind flange, and is thereby ready for use during all subsequent tank cleaning jobs.

Advantages of SafeTap®
The SafeTap® tapping procedure thus provides the following advantages and benefits to the tank owner and tank maintenance contractor:

  • Cold tapping procedure is completely safe – use of cutting liquid prevents heating of the material and inert gas provides extra protection against hazardous atmosphere.
  • Tapping one hole can be accomplished in as little as 15 minutes.
  • Tapping procedure allows the optimal placement of the appropriate number of tank cleaning machines, thereby ensuring the most effective cleaning result.
  • Installation of permanent flanged nozzles in the holes following the cleaning procedure results in faster and simpler mobilisation for all future cleaning jobs.
  • SafeTap® is developed to operate with a pneumatic drive thereby minimising both time and manual labour.

Consequently, use of the Oreco SafeTap® tool allows for the fast, effective and completely safe cold tapping of holes on the tank roof, thereby allowing the service provider to obtain the optimal cleaning result using automated tank cleaning systems from Oreco.

Published: 2003-01-22

Oreco A/S . Oldvej 1A . DK-3540 Lynge . Denmark . TEL. +45 4332 0200 . info@oreco.com

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