Intro4u2u

INTRODUCTION.

1. Recent inspection programs for metallic pressure containment vessels and tanks have revealed cracking and damage in a considerable number of the vessels inspected. Safety and hazard evaluations of pressure vessels, as also presented in OSHA Instruction PUB 8-1.5, need to consider the consequences of a leakage or a rupture failure of a vessel.

2. Two consequences result from a complete rupture:

* Blast effects due to sudden expansion of the pressurized fluid.
* Fragmentation damage and injury, if vessel rupture occurs.
3. For a leakage failure, the hazard consequences can range from no effect to very serious effects:

* Suffocation or poisoning, depending on the nature of the contained fluid, if the leakage occurs into a closed space.
* Fire and explosion (physical hazards for a flammable fluid).
* Chemical and thermal burns from contact with process liquids.
4. Only pressure vessels and low pressure storage tanks widely used in process, pulp and paper, petroleum refining, and petrochemical industries and for water treatment systems of boilers and steam generation equipment are covered in this chapter. Excluded are vessels and tanks used in many other applications. Also excluded are other parts of a pressure containment system such as piping and valves.

5. The types and applications of pressure vessels included and excluded in this chapter are summarized in Table IV:3-1. An illustration of a schematic pressure vessel is presented in Figure IV:3-1.

NOTE:   Though this review of pressure vessels excludes inspection or evaluation of safety release valves, the compliance officer should be aware that NO valves or T-fittings should be present between the vessel and the safety relief valve.

6. Most of the pressure or storage vessels in service in the United States will have been designed and constructed in accordance with one of the following two pressure vessel design codes:

* The ASME Code, or Section VIII of the ASME (American Society of Mechanical Engineers) “Boiler and Pressure Vessel Code.”
* The API Standard 620 or the American Petroleum Institute Code which provides rules for lower pressure vessels not covered by the ASME Code.
In addition, some vessels designed and constructed between 1934 to 1956 may have used the rules in the “API-ASME Code for Unfired Pressure Vessels for Petroleum Liquids and Gases.” This code was discontinued in 1956.

7. Vessels certification can only be performed by trained inspectors qualified for each code. Written tests and practical experience are required for certification. Usually, the compliance office is not equipped for this task, but is able to obtain the necessary contract services.