OHS Code Explanation Guide

Published Date: July 01, 2009
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Part 37 Oil and Gas Wells

Section 776 Drilling fluid

Figure 37.11 shows a typical drilling fluid or mud circulating system on a drilling rig.

Figure 37.11 Example of a typical mud circulating system on a drilling rig

Subsection 776(1)(a)

A system for pumping drilling mud typically operates at high pressure of up to 34,000 kilopascals (4,930 pounds/square inch). To ensure that a component of the system does not fail, all parts of the system must be rated at least equal to the maximum working pressure of the pump. This is also known as the “allowable rated working pressure”. Typically, this is shown on a metal plate affixed to the pump.

Before opening a pumping system or removing any cap, plug, plate or cover from a pump, the pressure within the pump should be bled off to atmospheric or as near atmospheric pressure as is practicable.

Subsection 776(1)(b)

The pump is the heart of the mud-delivery system and must be operational under all weather conditions.

Subsection 776(1)(c)

Figure 37.12 shows a typical pressure relief device.

Figure 37.12 Example of typical pressure relief device

Subsections 776(1)(d) and 776(1)(e)

No explanations required.

Subsection 776(1)(f)

Pressure relief devices are typically set to relieve at a pressure not in excess of 10 percent above the maximum working pressure of the pump.

Subsection 776(1)(g)

Every shear-pin-set relief device typically has a metal plate attached to it with holes drilled as a gauge for each size of shear pin to be used with the device and a table showing the pressure at which each size shear pin will shear. The shear pin must be of a design and strength specified in the manufacturer’s specifications (see Figure 37.13).

Figure 37.13 Example of sheer pin sizing gauge

Every shear-pin-set relief valve should have the valve stem and the shear pin enclosed in a manner that prevents contact with the valve stem and also prevents the shear pin from flying when sheared.

Subsection 776(1)(h)

Adequate drainage should be provided to prevent the accumulation of drilling fluids around pump bases.

Subsection 776(1)(i)

A reduction in piping size would impair the proper operation of the pressure relief device.

Subsection 776(1)(j)

The discharge of a pressure relief device is typically under high pressure. The sudden discharge of the device can result in wide movement of the piping if it is not secured.

Subsections 776(1)(k) and 776(1)(l)

No explanations required.

Subsection 776(2)

No explanation required.

Subsection 776(3)

A mud gun is typically used to mix the mud mixture in the rig tanks (see Figure 37.14). This is done to maintain a homogenous mix and ensure an even distribution of mud components. In carrying out this function, the outlet pressure can become high enough that the gun might become unmanageable by workers.

Figure 37.14 Example of a mud gun

Subsections 776(4) and 776(5)

A quick closing valve can produce momentary peak pressures that are beyond the capacity of a relief device to control.