Pressure Vessel Maker

【 abstract 】 in pressure vessel manufacture often encountered few problems are discussed, the analysis the current different opinions are put forward on the basis of personal point of view, the purpose is to reach consensus, ensure manufacturing quality products.

4.2 other problems
(1) material according to the actual situation, the welding process should be changed accordingly. (2) with advanced materials for alternative low-level materials, the test and inspection according to low-level materials shall still be carry out, and need no longer improve acceptance requirements. (3) material is different, its low temperature toughness reserves is different also, the corresponding minimum hydrostatic test temperature likely to change, at this time, should strictly according to GB 150 regulations. In addition, such as when thick thick more than the provisions of the cold roll GB 150 thickness, must be to the cylinder body eliminate stress heat treatment. When the steel plate to a certain thickness must also ultrasonic flaw detection. When need be appropriately raise the hydrostatic test pressure, some even will also lead to a significant change in the structure of the equipment.

5 hydrostatic test
Hydrostatic test as equipment manufacturing last procedure, in addition to the strength of the inspection equipment, will be to weld the density of the tight seal structure or performance inspection. At the same time, you can reduce or eliminate the residual stress, and make defects (crack) sophisticated passivation, so as to prevent the lower working under pressure to crack expansion or slow the expansion rate and improve its service life. In the reasonable under the opr will improve the fatigue life especially, and can improve the bearing capacity of the pressure vessel, blasting pressure will be improved obviously [19 to 21]. Visible, pressure test is of great significance, for the safety of pressure vessel using plays an important role. However, due to the 150-89 GB of strict regulations is not enough, make application, there have been some understanding of the confusion that in some cases the pressure has lost meaning. In addition, for the problem of equipment with pressure, standard of norms and appear too arbitrary, to manufacturing from some unnecessary trouble. Again, when shell material substitution, test pressure whether they should be have the change is also a worthy of discussion.

5.1 test pressure value and test stress limit [22]

GB 150-89 regulations hydrostatic test stress for:

P try = 1.25 p a [σ] / [σ] t (3)

When the vertical vessels lie for pressure, still should plan and test of the static pressure of the fluid column, namely:

P try = 1.25 p a [σ] / [σ] t + γ H (4)

GB 150-89 requirements will test stress increased to design the stress 1.25 times the strength of the inspection equipment, sealing structure and weld the density of the density of etc. Wen [22] analysis show that the type (3) the calculated value of just the minimum requirement of water pressure test, for vertical liquid gas or liquid containers filled with coexist, type (3) they can't meet the requirements, this time the application under pressure to replace the calculation of type design pressure:

P plan = p set γ 'h (5)
Type, γ?For the density of liquid materials; H of liquid materials for filling height. If buy pressure container lie at this time, the test pressure shall be [22] :

P try = 1.25 p plan [σ] / [σ] t-γ H (6)

Type, γ for hydraulic test of the medium density with; H for the container let empty always highly [22].

Obviously, type (6) than type (4) more appropriate, because according to type (4) calculation test pressure may to meet with the increase of the thickness of hydraulic test equipment, visible, with p plan instead of p set to calculate the test pressure is more reasonable, ASME [23], [and] BS 5500, AD [7] and so on also with p calculation program, although ASME also USES p set calculation, but it used only for vertical not filling liquid containers, not involve the static pressure of the fluid column. From foreign codes situation, they prescribed in the test pressure often are very high, the actual test stress multiples are close to the standard multiples. As in BS 5500, its p try for:

(7)Type, S for nominal thickness, C for additional quantity. To make containers can really tested, the shell with the design of rich used to withstand the test stress increase.

This shows, countries regulate are given as a standard test pressure lower limit for the provisions, basically to p plan instead of p set, and the actual test pressure are very high, the purpose is to make test stress design must be higher than the stress to test multiple containers, namely the actual test pressure generally are larger than equals p try. But GB 150-89 didn't seem to be very clear that for the execution of a lot of people think that not more than the 150-89 GB the calculated value of provisions. And the provisions of the 150-89 GB with p design calculate p try, in low voltage towers equipment to meet the increase in thickness of the equipment testing requirements, obviously this is not scientific. Published in GB 150-1998 [25] has the problem of change, but in vertical vessels for the provisions of the pressure down seems to be in still some problems.

Pressure on the stress control problems, the article discussed more, generally, according to GB 150-89 calculation test pressure may not have to check in stress, because test stress can not be more than 0.9 σ s or 0.8 σ s. But these articles in the analysis, is just to get test pressure take in GB 150-89 provisions on the calculated value of discussion. With 150-1998 GB of execution, the actual test pressure improve trend, so in the actual test pressure appear likely test stress more than 0.9 σ s or 0.8 σ s, thus affecting the safety equipment. From foreign codes situation, they also made limitation. ASME Ⅷ-1 though not to limit [23] directly, but it points out, intentionally or not, if more than according to the calculation formula of the test pressure test, makes a container apparent permanent deformation (plastic deformation), inspectors shall have the right to refuse to accept it, so actually or to test stress made limitation. So I think, test stress still should be 150-1998 GB limit. In order to improve the test pressure may, when necessary, according to the author formulas to calculate the hydraulic test pressure [19], in order to ensure that the test stress σ T than 0.9 σ s, namely:

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