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Mansa Musa was the ruler of the Mali Empire in West Africa. Details recorded here should be sourced; unknown information is left blank.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
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A hydrostatic test is a way in which pressure vessels such as pipelines, plumbing, gas cylinders, boilers and fuel tanks can be tested for strength and leaks. The test involves filling the vessel or pipe system with a liquid, usually water, which may be dyed to aid in visual leak detection, and pressurization of the vessel to the specified test pressure. Pressure tightness can be tested by shutting off the supply valve and observing whether there is a pressure loss. The location of a leak can be visually identified more easily if the water contains a colorant. Strength is usually tested by measuring permanent deformation of the container.
Hydrostatic testing is the most common method employed for testing pipes and pressure vessels. Using this test helps maintain safety standards and durability of a vessel over time. Newly manufactured pieces are initially qualified using the hydrostatic test. They are then revalidated at regular intervals according to the relevant standard. In some cases where a hydrostatic test is not practicable a pneumatic pressure test may be an acceptable alternative.[1]
Testing of pressure vessels for transport and storage of gases is very important because such containers can explode if they fail under pressure.
Hydrostatic tests are conducted under the constraints of either the industry's or the customer's specifications, or may be required by law. The vessel is filled with a nearly incompressible liquid – usually water or oil – pressurised to test pressure, and examined for leaks or permanent changes in shape. Red or fluorescent dyes may be added to the water to make leaks easier to see. The test pressure is always considerably higher than the operating pressure to give a factor of safety. This factor of safety is typically 166.66%, 143% or 150% of the designed working pressure, depending on the regulations that apply. For example, if a cylinder was rated to DOT-2015 PSI (approximately 139 bar), it would be tested at around 3360 PSI (approximately 232 bar).
Water is commonly used because it is cheap and easily available, and is usually harmless to the system to be tested. Hydraulic fluids and oils may be specified where contamination with water could cause problems. These fluids are nearly incompressible, therefore requiring relatively little work to develop a high pressure, and is therefore also only able to release a small amount of energy in case of a failure - only a small volume will escape under high pressure if the container fails. If high pressure gas were used, then the gas would expand to V=(nRT)/p with its compressed volume resulting in an explosion, with the attendant risk of damage or injury.
Small pressure vessels are normally tested using a water jacket test. The vessel is visually examined for defects and then placed in a container filled with water, and in which the change in volume of the vessel can be measured, usually by monitoring the water level in a calibrated tube. The vessel is then pressurised for a specified period, usually 30 or more seconds, and if specified, the expansion will be measured by reading off the amount of liquid that has been forced into the measuring tube by the volume increase of the pressurised vessel. The vessel is then depressurised, and the permanent volume increase due to plastic deformation while under pressure (permanent set) is measured by comparing the final volume in the measuring tube with the volume before pressurisation.[2]
A leak will give a similar result to permanent set, but will be detectable by holding the volume in the pressurised vessel by closing the inlet valve for a period before depressurising, as the pressure will drop steadily during this period if there is a leak. In most cases a permanent set that exceeds the specified maximum will indicate failure. A leak may also be a failure criterion, but it may be that the leak is due to poor sealing of the test equipment. If the vessel fails, it will normally go through a condemning process marking the cylinder as unsafe.[2][3]
The information needed to specify the test is stamped onto the cylinder. This includes the design standard, serial number, manufacturer, and manufacture date. After testing, the vessel or its nameplate will usually be stamp marked with the date of the successful test, and the test facility's identification mark.[3]
A simpler test, that is also considered a hydrostatic test but does not require pressure pumps, is to pressurise the vessel by filling it with water to a hydrostatic head by using a riser pipe connected to the tank and to physically examine the outside for leaks. This type of test is suitable for containers such as boat fuel tanks, which are not pressure vessels but must work under the hydrostatic pressure of the contents. A hydrostatic test head is usually specified as a height above the tank top. The tank is pressurised by filling water to the specified height through a temporary standpipe if necessary. It may be necessary to seal vents and other outlets during the test.[4]
Portable fire extinguishers are safety tools that are required in most public buildings. Fire extinguishers are also recommended in homes. Over time the conditions in which they are housed, and the manner in which they are handled affect the structural integrity of the extinguisher. A structurally weakened fire extinguisher can malfunction or even burst when it is needed the most. To maintain the quality and safety of this product, hydrostatic testing is utilized. All critical components of the fire extinguisher should be tested to ensure proper function.
Hydrotesting of pipes, pipelines and vessels is performed to expose defective materials that have missed prior detection, ensure that any remaining defects are insignificant enough to allow operation at design pressures, expose possible leaks and serve as a final validation of the integrity of the constructed system. ASME B31.3 requires this testing to ensure tightness and strength.
Buried high pressure oil and gas pipelines are tested for strength by pressurising them to at least 125% of their maximum allowable working pressure (MAWP) at any point along their length. Since many long distance transmission pipelines are designed to have a steel hoop stress of 80% of specified minimum yield strength (SMYS) at Maximum allowable operating pressure MAOP, this means that the steel is stressed to SMYS and above during the testing, and test sections must be selected to ensure that excessive plastic deformation does not occur.[citation needed]
For piping built to ASME B31.3, if the design temperature is greater than the test temperature, then the test pressure must be adjusted for the related allowable stress at the design temperature. This is done by multiplying 1.5 MAWP by the ratio of the allowable stress at the test temperature to allowable stress at the design temperature per ASME B31.3 Section 345.4.2 Equation 24. Test pressures need not exceed a value that would produce a stress higher than yield stress at test temperature. ASME B31.3 section 345.4.2 (c)
Other codes require a more onerous approach. BS PD 8010-2 requires testing to 150% of the design pressure – which should not be less than the MAOP plus surge and other incidental effects that will occur during normal operation.[citation needed]
Leak testing is performed by balancing changes in the measured pressure in the test section against the theoretical pressure changes calculated from changes in the measured temperature of the test section.
Australian standard AS2885.5 "Pipelines – Gas and liquid petroleum: Part 5: Field pressure testing" gives an excellent explanation of the factors involved.[clarification needed]
In the aerospace industry, depending on the airline, company or customer, certain codes will need to be followed. For example, Bell Helicopter has a certain specification that will have to be followed for any parts that will be used in their helicopters.[citation needed]
Most countries have legislation or pressure vessel codes which requires vessels to be regularly tested, for example every two years (with a visual inspection annually) for high pressure gas cylinders and every five or ten years for lower pressure ones such as used in fire extinguishers.[5] [clarification needed] Gas cylinders which fail are normally destroyed as part of the testing protocol to avoid the dangers inherent in them being subsequently used.[6]
These common US standard gas cylinders have the following requirements:[7]
Typically organizations such as DOT PHMSA, ISO, ASTM and ASME specify the guidelines for the different types of pressure vessels.
Hydraulic testing is a hazardous process and should be performed with caution by competent personnel. Adhering to prescribed procedures defined in relevant technical standards appropriate to the specific application and jurisdiction will usually reduce these risks to an acceptable level.
Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
A hydrostatic test is a way in which pressure vessels such as pipelines, plumbing, gas cylinders, boilers and fuel tanks can be tested for strength and leaks. The test involves filling the vessel or pipe system with a liquid, usually water, which may be dyed to aid in visual leak detection, and pressurization of the vessel to the specified test pressure. Pressure tightness can be tested by shutting off the supply valve and observing whether there is a pressure loss. The location of a leak can be visually identified more easily if the water contains a colorant. Strength is usually tested by measuring permanent deformation of the container. Hydrostatic testing is the most common method employed for testing pipes and pressure vessels. Using this test helps maintain safety standards and durability of a vessel over time. Newly manufactured pieces are initially qualified using the hydrostatic test. They are then revalidated at regular intervals according to the relevant standard. In some cases where a hydrostatic test is not practicable a pneumatic pressure test may be an acceptable alternative. Testing of pressure vessels for transport and storage of gases is very important because such containers can explode if they fail under pressure.
The lung float test, also called the hydrostatic test or docimasia, is a controversial autopsy procedure used in determining whether lungs have undergone respiration. It has historically been employed in cases of suspected infanticide to help determine whether or not an infant was stillborn. In the test, lungs that float in water are thought to have been aerated, while those that sink are presumed to indicate an absence of air. The test is not infallible and many factors can cause the test to give false positive or negative results. Decomposition may result in postmortem gas formation, allowing a non-aerated lung to float. During labor, air can be introduced to a deceased infant's lungs while moving through the birth canal. Lungs exposed to air do not always float. Große Ostendorf et al. showed the procedure gave a false result in 2% of cases. In a 1997 paper, J.J. Moar emphasises the risk of misdiagnosing live birth, writing that the "majority of new born infants seen at autopsy show signs of varying degrees of decomposition, as they are often found in garbage, wrapped in newspaper or plastic bags, or lying in an open field. Even microscopic putrefaction can cause unexpanded lungs to float, when gas formation may not be macroscopically apparent. Naturally, any attempts at resuscitation may partially expand the lungs of a new born infant, leading to further difficulty in establishing live birth." The difference between the lungs of a foetus and those of an infant was noted by the Ancient Greek physician Galen. The lung float test was described in the 1670s by Hungarian botanist Károly Rayger and first performed in 1681. German physician Johannes Schreyer performed a lung float test in 1690. The application of the lung float test to determine breathing and live birth has many spurious medico-legal considerations. In South Africa a foetus must have breathed to be considered a person under the law. Lung float tests are also used by forensic pathologists to determine if a subject drowned.
A pressure vessel is a container designed to hold gases or liquids at a pressure substantially different from the ambient pressure. Construction methods and materials may be chosen to suit the pressure application, and will depend on the size of the vessel, the contents, working pressure, mass constraints, and the number of items required. Pressure vessels can be dangerous, and fatal accidents have occurred in the history of their development and operation. Consequently, pressure vessel design, manufacture, and operation are regulated by engineering authorities backed by legislation. For these reasons, the definition of a pressure vessel varies from country to country. The design involves parameters such as maximum safe operating pressure and temperature, safety factor, corrosion allowance and minimum design temperature (for brittle fracture). Construction is tested using nondestructive testing, such as ultrasonic testing, radiography, and pressure tests. Hydrostatic pressure tests usually use water, but pneumatic tests use air or another gas. Hydrostatic testing is preferred, because it is a safer method, as much less energy is released if a fracture occurs during the test (water does not greatly increase its volume when rapid depressurisation occurs, unlike gases, which expand explosively). Mass or batch production products will often have a representative sample tested to destruction in controlled conditions for quality assurance. Pressure relief devices may be fitted if the overall safety of the system is sufficiently enhanced. In most countries, vessels over a certain size and pressure must be built to a formal code. In the United States that code is the ASME Boiler and Pressure Vessel Code (BPVC). In Europe the code is the Pressure Equipment Directive. These vessels also require an authorised inspector to sign off on every new vessel constructed and each vessel has a nameplate with pertinent information about the vessel, such as maximum allowable working pressure, maximum temperature, minimum design metal temperature, what company manufactured it, the date, its registration number (through the National Board), and American Society of Mechanical Engineers's official stamp for pressure vessels (U-stamp). The nameplate makes the vessel traceable and officially an ASME Code vessel. A special application is pressure vessels for human occupancy, for which more stringent safety rules apply.
Transportable pressure vessels for high-pressure gases are routinely inspected and tested as part of the manufacturing process. They are generally marked as evidence of passing the tests, either individually or as part of a batch (some tests are destructive), and certified as meeting the standard of manufacture by the authorised testing agency, making them legal for import and sale. When a cylinder is manufactured, its specification, including manufacturer, working pressure, test pressure, date of manufacture, capacity and weight are stamped on the cylinder. Most countries require diving cylinders to be checked on a regular basis. This usually consists of an internal visual inspection and a hydrostatic test. The inspection and testing requirements for scuba cylinders may be very different from the requirements for other compressed gas containers due to the more corrosive environment in which they are used. After a cylinder passes the test, the test date, (or the test expiry date in some countries such as Germany), is punched into the shoulder of the cylinder for easy verification at fill time. The international standard for the stamp format is ISO 13769, Gas cylinders - Stamp marking. A hydrostatic test involves pressurising the cylinder to its test pressure (usually 5/3 or 3/2 of the working pressure) and measuring its volume before and after the test. A permanent increase in volume above the tolerated level means the cylinder fails the test and must be permanently removed from service. An inspection may include external and internal inspection for damage, corrosion, and correct colour and markings. The failure criteria vary according to the published standards of the relevant authority, but may include inspection for bulges, overheating, dents, gouges, electrical arc scars, pitting, line corrosion, general corrosion, cracks, thread damage, defacing of permanent markings, and colour coding. Gas filling operators may be required to check the cylinder markings and perform an external visual inspection before filling the cylinder and may refuse to fill non-standard or out-of-test cylinders.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Mae Jemison, aboard Space Shuttle Endeavour in 1992.
