The Pressure Vessel RT Test article provides you with information about Radiography testing in the pressure vessel manufacturing process and related items in pressure vessel inspection.
Do you know what your pressure vessel RT test requirements are? Is full radiography mandatory for your vessel? When is full radiography mandatory? What are the acceptance criteria? What are the RT symbols?
So if you need this information, this article answers all of these questions.
We recommend that you to review this article in conjunction with the ASME Pressure Vessel Joint Efficiencies article.
Before going into the RT test, we need to know about joint categories. These categories are base on ASME Code Section VIII:
Category C and D are flange welds and nozzle attachment welds respectively
Longitudinal weld (Category A) is more critical because it is subjected to double the stress than Circ. Weld (Category B) and this the reason in different part of the ASME code, we have stringent rules in category A joints compared to category B joints.
When one of following conditions is existing, you need to do the full radiography:
As you see, the item numbers 1, 2 and 3 are really mandatory for a full RT test;
But pressure vessel manufacturers can make an optional decision for full radiography in item number 4
Pressure Vessel RT Test - Why do pressure vessel manufacturers want to spent more money for full radiography in item # 4?
Because the joint efficiency in the full radiography condition is 1, the higher joint efficiency in the pressure vessel wall thickness formula causes less wall thickness. The manufacturer might save lots of money with a lower thickness plate material.
But code has given some bonus to manufacturers in item 4, because it is not mandated to do full radiography in all butt welds. Manufacturers can do spot radiography in B and C joints with the same joint efficiency of item 1.
Item number 2 describes thickness limitations. Any pressure vessel material is designated to the specific P. Number by ASME section IX, so there are several tables in ASME Code Section VIII Div. 1 Subsection C, which determine this limitation.
For example, SA 516 material is P Number 1, and needs to be fully radiographed if its thickness is greater than 1.25 of an inch. At the same time, SA 204 material is P Number 3 and needs to be fully radiographed if the thickness is greater than 0.75 of an inch.
Acceptance criteria for welding defects in full radiography is stringent. These criteria are stated in UW-51 and UW-52 in ASME Code Section VIII Div. 1
It means there is a defect if interpreted based on the full radiography criteria in UW-51, and it might be rejected, but if it is interpreted by the spot radiography criteria in UW-52, it might be accepted.
The radiographic personnel need to be certified by the pressure vessel manufacturer according to their written practice.
Holding the ASNT Radiographic certificate is not enough
In fact, SNT-TC-1A can be used as a guideline for manufacturers to establish their written practice for qualification and certification of their personnel.
ASME Code Section VIII Div 1 mandates that all tests shall be done based on ASME Code Section V, article number 2.
Pressure Vessel Definition, ASME Code Section 8, Pressure Vessel Heads, Pressure Vessel Handbook, Spherical Pressure Vessel, Pressure Vessel Plate Material, ASME Pressure Vessel Joint Efficiencies, ASME Impact Test Requirement, Pressure Vessel Dimension Inspection, Vessel Pressure Testing, Third Party Inspection for Pressure Vessel, Inspection and Test Plan for Pressure Vessel
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