American Welding Society Forum
I’m involved in a discussion between two parties regarding the API 1104 limitations of individual or scattered porosity. We all agree on the size limits but have 2 questions on the maximum distribution of gas pockets shown in Fig 19 and Fig 20. (1999 Ed.). The sizes of gas pockets shown are not to scale. How are the fine, medium, large & assorted examples used for rejection or acceptance? What is the intent of the aligned examples with respect to the wall thickness. There is no reference in the porosity section discussing this.
Any input is appreciated.............
I've got an old edition of API 1104 which in paragraph 6.6.1 says that the dimension of any spheroidal pore (also called gas pocket) shall not exceed 1/8 of an inch or 25% of the pipe wall thickness, whichever is less.
Para. 6.6.2 says that the accumulation of pores shall not occupy an area larger than 1/2 of an inch in diameter, and that the maximum dimension of any pore in the accumulation shall not exceed 1/16 of an inch in diameter.
It goes on saying that the total length of the accumulation of pores in 12 inches of continuous weld length shall not exceed 1/2 of an inch.
Does this answer your question?
Giovanni S. Crisi
Sao Paulo - Brazil
Thanks for your reply.
My questions involve only the maximum distribution of gas pockets shown in Fig 19 and Fig 20. (1999 Ed.). I checked several older editions of 1104 and the figures are Fig. 15 & Fig. 16. All editions state that the maximum distribution of scattered (spherical in the older editions) porosity shall not exceed that shown in the figures.
Since the sizes of gas pockets shown in the figures are not to scale I don’t understand how the fine, medium, large & assorted examples are used for rejection or acceptance. The aligned examples (at the bottom of the figure pages) shows 1T, 2T & 4T. I am assuming “T” equals the wall thickness but there is no reference in the porosity section defining “T” or discussing the relevance of the spacing.
To all readers:
I have located some information from older inquiries to API that has shed some light on my questions. API intends for the user to apply judgement only, in compairing the examples (in the Figures) to the radiograph under evaluation. Regarding my question of the examples not being to scale, API says that all pores shown are smaller than 1/8" or 25% of the thinner wall thickness. (otherwise they would be subject to rejection due to the size limitations)
I am used to working with codes and specifications that are more definitative so I'm still open for comments from any API users on the application of this "judgement call".
I've got Figures 15 and 16 of my old edition of API 1104 under my eyes. Now get yours. You should have the standard with you, otherwise you won't be able to follow my idea.
If you observe on top of figure 15, there are two lines which start at the same point on the left end and gradually open, till there is a gap of, say, 3 millimeters (approx 1/8 of an inch) between them.
Under the bottom line there are several numbers: 1/8, 3/16, 1/4, 5/16, 3/8, 7/16 and 1/2 of an inch. A legend under the numbers says two things:
1st. The numbers mean the pipe wall thickness.
2nd. The gap between the lines is the maximum size of the pores for that particular wall thickness. Black circles above the numbers that mean the pipe wall thickness help you in having a visual idea of the pores sizes.
On the other hand, paragraphs 6.6.1 and 6.6.2 of my old edition state clearly which is the maximum pores size to be tollerated.
The pictures that represent the fine, medium, large and assorted porosity are not to scale, as you say. Their purpose is just illustrative. They are shown to help you in making your own idea on which porosity, i.e., size and concentration of pores, can be accepted and which can not.
Using the pictures, the two lines I've mentioned above and paragraphs 6.6.1 and 6.6.2 you should be able to take a decision.
Giovanni S. Crisi
Sao Paulo - Brazil
I’ve looked through a few older editions of API 1104. The oldest is the 14th. Ed. dated 1977 and none of them show the sizing chart you described. They all just show the 8 boxes with examples of distribution of porosity that are in question. It sounds like the chart is for calculation of 25% of the wall thickness since the 1/8” rule comes in to play once the wall thickness is greater than ½”. Just out of curiosity, which edition are you looking at?
The more opinions I get, I’m beginning to give in to the fact that the examples shown in the upper boxes are used for comparison by the film interpreter, with no relationship to the exact number of pores per unit of distance. The examples in the lower boxes do show the number of aligned indications allowed as well as the minimum distance between them, but the film interpreter again uses judgement to determine which example to use.
My client in question is welding from 3” o.d. X .300” up to 48” X 1.5” pipe, so we’ve got a tremendous range of not only thickness, but width of welds. API does have a provision which allows the company to reject acceptable welds if it feels a discontinuity is detrimental to the weld. With respect to porosity this provision is usually used when a pore may be acceptable in size, but has sufficient radiographic density to suggest that it is larger in the dimension parallel to the plane of the source of radiation and not accurately shown on the radiograph. I wanted to avoid using this provision until all parties agreed on the proper use of the figures and examples in question. The two things in our favor are the fact that all welding is being done indoors and we have more smaller diameter / thinner wall pipe than the heavy stuff.
The rounded indication acceptance in ASME VIII, Div.1, Appendix 4, for example, is so much easier for me to work with and it address the same issues.
I appreciate your opinions and help on this question.
The API 1104 edition I've got is an old one: 1968.
I think we're saying the same thing with different words. I say that figures 15 and 16 of the old editions (19 and 20 in the newer ones) are there for "illustrative purposes etc. etc ............", while you say that "they are use for comparison etc. etc ............"
So, we agree that they're aimed at helping the inspector in making up his mind on whether the weld is acceptable or not.
API 1104 was made specifically for oil and gas pipelines, and should be used for that purpose. Of course, nobody can preclude you from using it for other type of piping if you want to, but in those cases you should follow the applicable code or standard, like for example ASME B.31.
For chlorine piping there is a standard issued by The Chlorine Institute, and for pure oxygen there's a standard issued by The Compressed Gas Institute.
ASME VIII, on the other hand, was made for unfired pressure vessels and doesn't apply to piping.
Giovanni S. Crisi
Yes, I believe we are in agreement on the purpose of the porosity examples we’ve been discussing. The scope of this particular project does fall under API 1104. The components built for this contract are all shop fabricated and installed in the field by others. They mainly consist of compression, transmission & distribution piping. The larger diameter piping is used for launchers, receivers and slug catchers.
I cited ASME porosity criteria as an example only for the ease of use. (Or at least it is for me). And actually I do inspect quite a bit of piping which falls under ASME VIII. It all depends where the jurisdiction of the code stops, which is stated on the Data Sheet. In many cases this is at the nozzle flange face, but the code can extend through interconnecting piping in say stacked shell and tube exchangers. Many vessels designed for sour and lethal service have a certain amount of external piping as well, which is under ASME VIII. But the piping must appear on the Data Sheet.
Thanks for your continued interest in this topic.
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