Non-destructive testing regarding the coil weld joint coefficient of 1.0
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The equipment is a Class I vessel; the external coil has a diameter of φ34×4 and a length of approximately 19 meters. The other details are as shown in the diagram. May I ask whether it is reasonable to use a coefficient of 1.0 for MT calculations? What do everyone think about this issue?
Girth weld, single-sided welding with double-sided formation; not a Category 1 material, so there is no need for a 1.0 coefficient.
Since the coil is outside the container and the medium is hot water, it is possible to conduct an MT inspection. The joint coefficient refers to the coefficient for longitudinal seams; a value of 1.0 is appropriate.
100% radiographic testing should also be conducted on the coil section
The drawings are fine; everything is correct. It’s your understanding that’s wrong.
This post was last edited by zxhslm on 2021-5-31 16:17. The welding joint coefficient used in the formula for calculating the cylinder wall thickness is the coefficient for longitudinal welding joints; since the outer coil is made of seamless steel pipes, the welding joint coefficient is 1.0. Although the coil is outside the equipment, the requirements for surface inspection are somewhat low; 20% RT is still required.
With such a thick coil, can the heat exchange efficiency be good? The small diameter of the coil cavity is unacceptable. To prevent leakage at the top, the operating pressure is very low; using 100% magnetic powder is also acceptable.
This external coil is probably not intended for heat exchange.
This post was last edited by Forgetting = Forgetting on 2021-6-4 at 11:52. 1. For the butt joints of pressure vessels, methods such as RT/UT/TOFD should be used. 2. The non-destructive testing methods, proportions, and acceptance criteria for the welding joints of pipes with a diameter less than DN250 are specified by the designer or relevant product standards. Choosing 1.0 means that the weld is equivalent to a fully penetrated weld, requiring 100% radiographic or ultrasonic testing. MT is a surface non-destructive testing method, and it cannot replace the aforementioned testing methods. Due to limitations in detection accuracy and methods, MT cannot accurately detect surface or near-surface defects at this size, let alone defects in deeper layers; therefore, coefficients of 1.0 or 0.85 are used. For RT testing, combining it with 100% PT provides more reliable results. If it is not possible to perform flaw detection between the coil and the cylinder, then the design of the drawing needs to be modified.