Few in the industry truly understand pressure hazards unless they’ve seen or been victim to an accident involving them.
By John Fowler, CSP, CMSP
Pressure is a hazard we work around every single day regardless of whether we are working on a pump rig or a drilling rig.
But because we are so used to it, there is a tendency to become complacent around it. Complacency is when we become so used to a routine hazard that we no longer consider it a hazard. And while most of the time there are no issues, if we are not inspecting and properly maintaining our equipment, hoses, fittings, and valves—they could become a risk to our safety.
There are many pressurized systems on our pump and drilling rigs, and this article will focus on the air, fluid, and hydraulic systems we use in the field just about every day.
Air compressors are used all the time on our sites. Air pressure can be used during drilling operations to lift mud and cuttings to the surface, to power downhole hammers, or once the well has been drilled and constructed, to clean out the well. Sometimes air pressure is used to power small transfer pumps or even used to open and close valves on our equipment.
We often become so used to our compressed air systems that we don’t take the time to really inspect and maintain them like we should. But what are the hazards that come with compressed air, and what can we do to control those hazards?
First, let us look at the compressor and receiver tank. Your air system should be visually inspected before work begins. Remember: “psi” stands for pounds per square inch and just look at all the square inches of your air system and think about what would happen if any part of that system failed.
Besides looking at the overall condition of the compressor and receiver tank, look at the pressure relief valve. Air systems need to have relief valves to avoid building more air pressure than the system is safely designed to handle. Typically, the relief valves are set at a maximum of 10% over the designed system maximum pressure.
Once a pressure relief valve has been professionally inspected or adjusted, a small wire seal is put on the valve itself. If you see that the seal is broken or missing, it is a good idea to have a professional look at the relief valve to make sure it is still adjusted correctly. And always remember to keep the pressure relief valves pointed in a safe direction!
Next, inspect your air hoses to ensure they are in good condition and rated for the pressure that your system produces. They should be inspected for overall condition, looking for any damaged or worn spots and for any metal wire showing.
Look for any bubbles in the rubber outer layer and look for any “wet” spots on the hose or on the ground underneath the hose. The compressed air in the air system is mixed with small amounts of oil and condensate, so if you see a dark or wet spot on your air hose or on the ground underneath the hose, there is a good chance there is an air leak. Change out your hose.
If a hose does burst, the energy in a whipping unsecured hose could easily cause serious harm to anyone in its path. It is helpful to think of compressed air as a giant spring, and just like a spring, the more it is compressed, the more energy is being stored. If that air is suddenly released, the result will be uncontrolled and violent.
OSHA 1926.302(b)(7) states that “All hoses exceeding 1/2-inch inside diameter shall have a safety device at the source of supply or branch line to reduce pressure in case of hose failure.”
The recommended way to secure your air hose is to use whip checks or safety chains. Just keep in mind that the whip checks or safety chains need to be secured to an attachment point that will not break off when subjected to the force of the broken air hose. A common industry best practice is the use of braided wire whip socks that extend down the hose several feet and are designed so that the more force that is applied, the stronger they grip the hose.
This style of whip sock also has two attachment points that should be attached to two separate anchorage points. When installing whip checks or whip socks, remember to use the correct size for the hose you are using. Also, whip checks should have a minimum amount of slack when installed correctly. Too much slack and the momentum of a broken air hose could potentially break the whip check.
Drilling Fluid System
Now let’s look at a fluid system—the best example of which is our drilling fluid system. The main items to look at and inspect are your mud pumps, valves, and fittings.
Before beginning your inspection, you need to determine the maximum pressure the entire system is going to see. You
can figure this out by either knowing the maximum pressure of the pump you’re using or the maximum amount of pressure you want to exert on the formation. Sometimes the well itself may have pressure if you’re dealing with a column of water or grout or if you are dealing with artesian water pressure. Once you know your pressure, you need to make sure the entire system you are using can handle that pressure.
Regardless of whether it’s an air system or a fluid system, the component with the lowest pressure rating determines the maximum pressure the system can handle. Look at the valves, hoses, and the fittings. What is their pressure rating? It’s tempting to replace a valve with the first one you get your hands on from the local hardware store, but that can lead to trouble.
There are low-pressure valves and high-pressure valves, and the ratings are stamped on the body of the valves themselves. What you will typically see stamped on the valve body is something like 600 WOG or 2000 WOG. Here WOG stands for water, oil, gas. This is telling you the valve can withstand water, oil, and gas at the specified pounds per square inch (psi), but not steam. Be sure that the valves are rated for the maximum pressure the system can produce—not just what you think will be the operating pressure.
This same idea also applies to the fittings used in your system.
When we talk about fittings, we typically talk about Schedule 40 or Schedule 80 pipe. Schedule 40 and 80 refer to pipes and nipples and their relative thickness. Most of the time either schedule has a high enough pressure rating to be used on our fluid systems, but always verify that is the case.
What we really should be talking about are cast fittings versus forged fittings. Cast fittings are low pressure and usually rated for 300 psi or less. Forged fittings are high pressure and are usually rated in the thousands of psi range. How do you tell the difference? Forged fittings are usually stamped with a forge symbol—a diamond or triangle—while cast fittings are not.
A low-pressure fitting on a high-pressure system is an accident waiting to happen, so look at your fittings and know their pressure ratings.
The two types of pumps we typically use are centrifugal pumps and positive displacement pumps.
Centrifugal pumps are the “trash pumps” typically used to mix mud or transfer fluid from one tank to another. They are low-pressure pumps and work by using a spinning impeller to fling the water or drill mud out the fluid outlet using centrifugal force. The pump doesn’t mechanically push the water, so if a centrifugal pump is dead-headed, meaning the outlet valve is closed and there is nowhere for the water to go, the impeller will keep spinning and the water will begin to heat up.
A centrifugal pump will build pressure up to a certain psi, depending on the pump, and then stop building pressure. The main hazards with dead-headed centrifugal pumps are damaging the impeller and the possibility of the heat that will be generated turning the water to steam.
If we are using a positive displacement pump such as a duplex or triplex pump, the water is moved by pistons which mechanically push the water out the discharge line. If a positive displacement pump is dead-headed, the pressure will rapidly build until it causes something to fail.
Because of this, it’s critical that positive displacement pumps have a pressure relief valve just like an air system. Typically, a piston pump has a pressure relief valve that either releases pressure into the suction side of the pump or out onto the ground. The pressure relief valve needs to have the correct adjustment or shear pin for the desired pressure, so only use what the manufacturer recommends. If a shear pin is replaced with something such as a bolt, for example, the valve will no longer function correctly, and the pressure will build until there is a mechanical failure and you have an unexpected and uncontrolled release of pressure.
Lastly, hydraulic hoses should be inspected every day as part of the pre-work inspection and throughout the day as we work around our equipment.
Hydraulic hoses should be inspected for any metal showing, leaks, damaged fittings, kinked hoses, and anything else that doesn’t look right. Never use your hand or any other body part to look for a hydraulic leak.
Our hydraulic systems operate at thousands of psi and a pinhole leak in a hose or fitting that comes in contact with human tissue could potentially inject that hydraulic oil into your body. Injected hydraulic oil will cause severe injury and lead to the removal of any tissue that has been contaminated with hydraulic oil and possibly amputation of that body part. If you’re concerned that there might be a hydraulic leak, use a two-by-four or piece of cardboard/paper to detect the leak. Again, never use your hands or body.
We deal with the hazards of pressure every day we work, and because of this we tend to get complacent. Inspect your air and fluid pumping equipment, hoses, valves, and fittings to ensure they are in good condition and rated for the correct amount of pressure.
If you’re ever tempted to use a component that is underrated for the expected pressure, think about what psi stands for: pounds per square inch. How many square inches of steel are there on that tank, that hose, or fitting? And if there is a failure, how many tons of pressure and pounds of steel would be coming your way?
Pressure can be safely controlled, and most of the time it is. But once again, avoid becoming complacent because if there is a problem involving pressure, the results have the potential to be catastrophic.
John Fowler, CSP, CMSP, is safety manager at National Exploration, Wells & Pumps Inc. in Elko, Nevada. Fowler serves on NGWA’s Safety Subcommittee and once chaired it. He is a regular safety workshop presenter at Groundwater Week and can be reached at email@example.com.