Burst hoses

Hoses have failed while tank trucks or cars were being filled or emptied for all the reasons listed in Section 7.1.6, in particular because damaged hoses or hoses made from the wrong material were used. However, 

Plant instioictions stated that a portable barrier should be put in front of tank trucks being filled, but the barrier was not being used. However, if it had been in use, the driver might have removed it. 

A device that can be fitted to a tank truck to prevent anyone from driving it away while a hose is connected is described in Reference 2. A plate is fixed in front of the hose connection. To connect the hose, this plate has to be moved aside, and this applies the brakes. Reference 3 describes a special type of hose that seals automatically if it breaks there ai e also other types. 

Remotely operated emergency isolation valves (see Section 7.2.1) should be fitted on filling lines. If the hose breaks for any reason, the flow can be stopped by pressing a button located at a safe distance. Reverse flow from the tank truck or car can be prevented by a check valve. 

Note that it is not necessary to ground tank trucks containing liquefied flammable gases because no air is present in the tank. 

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Figure 4. Burst hose as a result of excessive pressure from pumping highly viscous oil (NOAA 2010).

Master curves can be used to predict creep resistance, embrittlement, and other property changes over time at a given temperature, or the time it takes for the modulus or some other parameter to reach a critical value. For example, a mbber hose may burst or crack if its modulus exceeds a certain level, or an elastomeric mount may fail if creep is excessive. The time it takes to reach the critical value at a given temperature can be deduced from the master curve. Frequency-based master curves can be used to predict impact behavior or the damping abiUty of materials being considered for sound or vibration deadening. The theory, constmction, and use of master curves have been discussed (145,242,271,277,278,299,300). 

Berth operator should possess a supplier s certificate for any hose forming part of the pipeline confirming that tests have shown it is unlikely to burst in service. 

Figure 7-3. This hose burst, injuring the operator. It was the wrong type, was damaged, and was badly located.

The hazards of water hammer are described in Section 9,1,5 and the hazards of ice formation in Section 9,1,1, This section describes some accidents that have occurred as the result of the sudden vaporization of water, incidents known as boilovers, slopovers, foamovers, frothovers, or puking, Boilover is used if the tank is on fire and hot residues from the burning travel down to the water layer, Slopover is often used if water from fire hoses vaporizes as it enters a burning tank. Sections 9,1.1 and 12.4.5 describe incidents in which vessels burst because water that had... 

The minimum bend radius for flexible hose varies according to the size and construction of the hose and the pressure under which the system operates. Current applicable technical publications contain tables and graphs showing the minimum bend radii for the different types of installations. Bends that are too sharp will reduce the bursting pressure of flexible hose considerably below its rated valve. 

Passage of thionyl chloride through a flexible metal transfer hose which was contaminated with water or sodium hydroxide solution caused the hose to burst. Interaction with water violently decomposes the chloride to hydrogen chloride (2 mol) and sulfur dioxide (1 mol), the total expansion ratio from liquid to gas being 993 1 at 20° C, so very high pressures may be generated. 

Braiding hoses with wires to resist high burst pressures or for external protection is common, using a braiding machine. The wires used, usually of steel, will be either zinc- or brass-coated to achieve adhesion during vulcanisation. The gauge of the wire and its tensile properties will be matched to the expected service demands for the hose. 

Kelly hose burst during well control procedure, Kelly cock and in-line safety valve could not be closed. 

Hoses built to United States standards have a four-to-one pressure design safety factor. This means that the maximum allowable working pressure (MAWP) must be one-fourth the hose s minimum burst pressure. This rating is generally specified at 72°F, and many users are unaware that, as the operating temperature increases, the hose assembly s MAWP decreases. [11]... 

Mechanical perfoimance (tensile, flexural, impact, bursting pressure, and compressive strength), resistance to heat, thermal expansion coefficient, heat distortion temperature, maximum working temperature, burning class, UV stability, and working stress are the most important parameters characterizing performance requirements of pipes and hoses and are used as selection criteria. Fillers can help to fulfill these requirements, but are underutilized. Fillers seem mainly to be used to lower cost. 

Some applications require flexibility to bend and curl the hoses. To accomplish this, the extmded and sintered tubes can be convoluted in a separate step. The tube is passed through a heated die, which melts the PTFE and creates a spiral peak and valley pattern into the tube. A key requirement of the convolution process is to assure that the wall thickness remains uniform, in other words, the tube is not stretched. Any thinning of the wall will weaken and reduce the burst pressure of the hose. Figure 5.31c shows an example of convoluted tube, which is partly braided with stainless steel. 

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