Document 9Jwn9Yv3p5b6zw5mpp6pb0KV5

should be tested for flammable and toxic gases, and for inadequate oxygen These tests must be repeated at intervals to make sure that conditions remain safe while men are in the vessel Au should be introduced to make suie there aie several air changes per minute m the vessel After all preparations for entiy are made, the supervisor of the area should check that the vessel is safe, that all lines are closed off, that power sources are locked out, that ven tilation and personal protective equipment are adequate, and that safe work procedures are planned He can then issue a "vessel entry permit," a note that ceitifies all precau tions have been earned out Men should not be lowered into vessels without facilities foi them to climb back out themselves (if it can be avoided) Straight ladders 01 rope or chain laddeis with rigid wood lungs should be provided Also, men should not be tequired to go into an opening that they must squeeze through They cannot be removed quickly in an emergency Another necessary precaution is to have men don safety harnesses attached to life lines before entering any vessel An observer equipped with similar respnatory protection and harness with a lifeline should be stationed outside the vessel This man should also have some device for signaling for mote help, one man's efforts might prove inadequate Depending on the previous content of the vessel, the man entering the vessel should be equipped with a vapor-proof flashlight or vapoi-pioof low-voltage extension light At times, a chemical piotective suit is advisable The method of cleaning depends on the use of the vessel If it has contained peti oleum or chemical products, the vessel may be filled with water, a caustic solution, or a neutralizing agent to remove sludge and ad hered materials Vessels used for flammable liquids should be washed, steamed and/or ventilated until a test with an appioved ex plosion meter shows the level is safe (See Chapter 42, "Flammable and Combustible Liquids ") Hydrostatic tests If a pressure vessel is so constiucted that an intei nal inspection cannot he made period ically (length of the intervals depending on the corrosivity of the contents), it should be subjected to a hydrostatic test if the weight of water will not m turn set up damaging stresses In this latter case, a pneumatic test can be applied See ASME Code, Sec tion VIII Compressed gas or air should never be used to test an unfired pressure vessel above its safe working pressure, although it can be used to test foi leaks at pressures below the working pressure Great care must be used because a vessel may fail under test and shatter Testing should follow procedures in the ASME Codes and be under the supervision of qualified personnel The required pressure for a standard hydro static test is noimally 13* times the maximum allowable woiking pressure of the vessel being tested Division 2 provides for the establish ment of upper limits by the design engineer, in terms of stress-intensity limits relative to the yield stiength at test temperature In spection of Division 2 vessels is made at a pressure equal to the greater of the design pressure, or of the test pressure Test areas should be isolated as far as possible from other operations and suitable barncades should be provided for protection of personnel and valuable equipment This is especially important when conducting proof tests and tests to destruction All personnel should keep clear of the vessel under full test pressure and no one should be allowed to appioach the vessel until the pres sure has been reduced to, or is very close to, the maximum allowable working piessure Detecting cracks and measuring thickness Piessure vessels used to piocess gases or oily materials may have veiy small leaks which will not show under hydrostatic tests To detect them, a small amount of ammonia can be released inside the vessel and com pressed air is then applied until a maximum pressure of 50 peicent of the woiking pressure is attained A swab soaked m hydrochloric (muuatic) acid is passed ovei all seams and other suspect areas Leakage will be indi cated by a white vapor (ammonium chloude) formed by contact of escaping ammonia and the acid Using a burning sulfur stick is also effective--a change in the flame mdicat- 1405