According to the United Nations Conference on Trade and Development (unctad.org), around 80% of global trade by volume is carried by sea. While commodities like grain, ore, and coal comprises much of this cargo, various petroleum products (crude oil, refined gasoline and diesel, LNG, etc.) are also shipped in large volume. In 2018, The United States imported an average of nearly 10 million barrels of petroleum products per day, and exported another 7.5 million barrels (per the U.S. Energy Information Administration), mostly by ship. Large tanker vessels also transport liquid chemicals such as fertilizers, pesticides, and petrochemicals. All of these liquids require flexible dock hoses for cargo loading and unloading. While most dock hoses are metal, rubber, or composite constructions, many terminal operators prefer using stainless steel corrugated metal hose in their facilities for the numerous advantages it offers.
By Frank Caprio, Corporate Trainer, Hose Master
Stainless Steel corrugated metal hoses offer a number of advantages, such as:
- Fire safety
- Excellent corrosion resistance (can safely be used with biodiesel blends)
- Superior resistance to weathering (degradation caused by temperature extremes, ultra-violet radiation, and ozone)
- Good flexibility
- No media permeation through the hose wall
- A very compact end fitting configuration (improves maneuverability during connecting and disconnecting)
Because these corrugated metal dock hoses can initially cost more than non-metallic hoses, they must provide better value by functioning safely, efficiently, and reliably for a long time. In order to ensure maximum service life (and value), the user should follow these guidelines for installation, inspection, testing, and storage.
New Hose Inspection
When specifying and ordering new dock hoses, the user should make sure to stipulate if the assemblies must conform to any industry standard (ABS, ISO, ASTM, etc.), as this can affect the documentation that is required for proper conformance and record keeping. For example, dock hoses transferring oil or refined petroleum products are typically required to be tested and tagged per Coast Guard requirements as specified in CFR 2010 Title 33, Vol 2, Part 154 (33 CFR 154.500). This regulation specifies the allowable working and burst pressures for dock hoses as well as testing and tagging requirements. It is important to note that, during testing, the hose may not be covered in any way that might prevent a leak from being detected. This means that any abrasion-resistant covers should not be applied until testing has been completed.
Upon receipt of a new assembly, the hose should be inspected as follows:
- Immediately inspect the hose assembly for any signs of damage during transit; dents, broken braid wires, or damaged sealing surfaces (threads, flange faces, etc.) are all cause for rejection.
- Verify the hose assembly is correct (size, length, end fittings, pressure rating) and that the fittings are properly aligned/oriented. Floating flanges should rotate freely.
- Verify the hose is tested and tagged properly; the Maximum Allowable Working Pressure (MAWP) and the media to be conveyed should be clearly visible. Many regulations also require the tagging to include the manufacturer and the date the assembly was fabricated.
Corrugated metal hoses can generally be put directly into service, but be aware that certain chemicals or other high-purity liquids may require the hose assembly to be specially cleaned before the first cargo is transferred. Some customers add various protective covers to the exterior of the assembly as an added barrier against external abrasion. A polyethylene spiral hose wrap would be a good option here, as the hose exterior is still visible to the operator, who should conduct routine inspections for any signs of damage or wear.
During installation and use, it is important that the assembly be handled properly in order to prevent any damage. Here are a few recommendations:
- Remove any sharp obstructions such as old anchor bolts or jagged dock sidings from around the loading area.
- Do not bend the hose beyond the minimum recommended bend radius, as excessive metal fatigue can shorten the service life of the assembly:
- If required, the addition of an external stripwound bend restrictor on one or both ends of the assembly can prevent over-bending.
- Make sharp bends using rigid pipe elbows where possible.
- Make sure the hose is properly supported during loading, installation, etc. Never lift a hose using a single sling. Instead, use a series of slings and supports in order to maintain an even, gentle bend. Urethane hose saddles are available for this purpose.
- Avoid stretching the assembly to make a connection.
- Make sure the assembly is not being twisted during installation, which puts additional stress on the welded connections. If the hose is twisted while in service, then low-torque swivel joints may be required on dockside piping connections to accommodate this movement. Multi-plane swivels are recommended to prevent any torsional stress from being applied to the hose.
- Follow the gasket manufacturer’s recommendations for proper bolt tightening of flanged connections to ensure an even, leak-free seal.
- After transferring cargo, follow established protocol for emptying, purging, and capping the assembly to remove any residuals and to prevent the entry of foreign matter.
Hoses should be stored in a designated area, away from any potential sources of corrosion or mechanical damage. Establishing a hose storage program ensures proper hose management practices while also increasing safety by eliminating a tripping hazard. Hoses are more easily inspected and monitored to determine if a sufficient number of hoses are in usable condition, and properly stored hoses are more easily moved to the loading area without fear of damaging the assembly. Do not hang stored hoses on a hook, in a pile, or in any way that would cause the assembly to overbend. If the hose ends are not capped, the hoses should be stored with the ends off the ground but facing downward, to minimize any contaminants from entering the hose.
Routine testing of dock hoses ensures they are capable of withstanding the system pressure. Typically, dock hoses should undergo annual hydrostatic testing to one and one-half times the maximum media pressure. Hose tagging often must specify the last date the assembly was tested, and may also show the date the assembly should be replaced. More frequent testing may be required depending on the criticality of service. It is advisable to check with the local authorities (Coast Guard, et al) to ensure all testing conforms to local regulations. Other test methods are also available; consult the manufacturer for specific testing options and considerations.
It is sound operating procedure for the operator to routinely inspect dock hoses before putting them into service. Here are some things to look for that could indicate the assembly needs to be retired:
- Broken or missing braid wires
- Signs of twisting (torque)
- Signs of corrosion; chemical residue on exterior, product leakage, etc.
- Overbending or stretching an assembly
- Fitting damage
- Baggy, deformed, or twisted braid
If you are not sure about any of the above recommendations, consult the vendor for assistance. The salesperson can usually provide great insight to help extend hose life and prevent problems before they occur. Also, there are plenty of ways to reduce the up-front cost of a corrugated metal dock hose, but each of these cost-saving short cuts reduces the service life of the assembly. Ask questions about how the hose is made, what features it has, and who is doing the fabrication. Is the welder properly qualified? Can the vendor provide the various materials, testing, and welding certifications that may be required? Fabricating dock hoses from the best materials using qualified welders maximizes the overall value and reduces costs over the long run. Saving a few dollars by sacrificing safety and service life just does not add up.