With reference to the technical article (within the Coade web) on the sif’s for B16.9 welding tees I would like to question how "real" this issue is? I would like some feedback from anyone with experience on this issue.
• Have here been any failures caused by this?
• What is the response from manufactures when asking for Welding tees that fully comply with B16.9

Please note that the article you reference is over three years old. A more current discussion on this topic can be found in this forum, by clicking this link . (And even this was posted before the release of Version 4.40, which addresses this "Code" change.)

CAESAR II follows the current code. This means that it is assumed that your tee doesn't meet the dimensional requirements, and you end up with a higher SIF. If you do meet the dimensional requirements, then you can flip the configuration switch and have CAESAR II compute the lower SIF (which is what all prior versions of CAESAR II assumed).

The other way to obtain the lower SIF values is to specify the two dimensions on the dialog. If these values meet the requirements of Appendix D,
CAESAR II will automatically compute the lower SIF.

As to your last two questions, I'm not in a position to offer advice here.

Hello Nigel,

We do not see failures in B16.9 Welding Tee's (there were quite a few before the Code reduced the allowable stress for 335, P-11 (1 1/4 Cr, 1/2 Mo) material - due to creep-fatigue interaction). We do see failures in fabricated branch connections (reinforced and non-reinforced) but we think these reflect welding workmanship more than anything else.

Something that should be considered is that the B31 Codes DO NOT SPECIFY requirements for Tee's, so the Manufacturers of Fittings (Tee's) DO NOT (are not asked to) comply with the B31 Codes. The B31 Codes refer to ANSI Standard B16.9 for standard welding fittings. It must be understood that VERY LITTLE geometry is standardized by B16.9. End-to-end (and centerline-to-end) dimensions are standardized, and the "squareness tolerances" of the fittings are standardized - nothing else, including crotch radii, thickness or shape is standardized. If you compare the shape of several Tees's that DO COMPLY with the requirements of B16.9, you will see some of them are quite "spherical" at the "cheek" area, some are barrel shaped and some are very cylindrical on all their "legs". But they all are B16.9 Tee's.

The B16.9 fittings (e.g., Tee's) "must be able to be shown" to be as strong (against internal pressure loading) as the straight pipe welded to them - i.e., the pipe will burst under pressure before the mating fitting ruptures. The wall thickness is not standardized throughout the fitting but the manufactures are required to match the wall thickness (schedule) at the weld line so there will be good fit-up (minimum mismatch). Most fitting manufacturers have traditionally made fittings that are thicker than needed to pass burst tests and they line bore them to match the mating pipe schedule.

Most of the SIF's that are (still) in the B31 Codes are those that came out of the Markl (and colleagues) experimental work that was the basis of "new" Code fatigue rules in 1955 (B31.3 and the B31 Mechanical Design Committee are actively working to update the rules). Markl's work was done at the facilities of Tube Turns Company, so the testing used that company's fittings (and all the fittings and pipe were NPS 4, standard schedule, A-53, Gr B). Since NO TWO MANUFACTURERS MAKE FITTINGS THE SAME SHAPE (except to comply with B16.9 Standards) the tests and the fatigue data (and SIF's) that resulted from the testing could, strictly speaking, be applied only to the test sponsoring company's product. It should be recognized that given the WIDE variation in the shapes of the fittings (especially Tee's and reducers) provided by the manufacturers, the Appendix "D" data may or may not be accurate. B31 Codes have always told the designer that if he/she had better data to apply (these days it would be from FEA) then the designer was free to employ this data. Having no better data, the Code SIF's (and FF's) are better than nothing. Some time after the original fatigue rules (of Appendix "D" etc.) were included in the Code, words were added (in several "phases") to adjust for crotch radii, pressure stiffening, flanged ends, weld-on and weld-in branch fittings, etc. As an aside, The manufacturers of proprietary weld-on and weld-in fittings have had to perform their own tests and determine SIF's for their products (they will provide these for you if you request them).

The flexibility factors (FF's) for Tee's were always (even before Mark's quantification) known to be other than 1.0 (when compared to straight pipe), but they were left at 1.0 for various branch connections. That is USUALLY conservative.

The B31 Codes will be changing to reflect a more contemporary understanding of how various piping components perform in service. I am confident that as the B31 Codes adopt new rules, Caesar will exactly reflect these new rules.

Just my opinion.

Best regards, John.

Dear John Breen, and nigel marsh

WFI's major product line is integrally reinforced branch outlet fittings which is the topic that will be discussed in this paper. The paper will describe what a branch outlet fitting is, why it is used, how it can be determined to be code worthy and the importance of stress intensification factors. When I refer to the Code, I will be referring to the ASME B31.3 Piping Code. You should also be aware that other ASME piping codes, B31.1, B31.4, B31.8 etc. have similar requirements.

I will also establish that branch outlet fittings are engineered products that have their own unique and proprietary shapes, and that WFI branch outlet fittings, PIPETS®, have certain engineering and cost saving features that other manufacturer's designs don't have.

I believe it is important that before I enter into this discussion of branch outlet fittings that I first define a piping branch connection, and then provide you with a little history of the various types of reinforcement that have been used and may still be used to strengthen piping branch connections.

A piping branch connection is simply the joining of two pieces of pipe at some predetermined angle to split the flow of the fluid, gas or particulate flowing in the piping system. Anytime a hole is cut in one pipe to join another to it, the pipe with the hole cut in it has been weakened. The pipe with the hole is commonly referred to as the run pipe. If pipes of the same schedule are connected, welded together without any additional reinforcement at the point of attachment, failure will occur at the point of attachment at a pressure which is lower than the failure pressure of an unweakened pipe.

Early piping systems were simply constructed by connecting one pipe to another without any reinforcement at the point of attachment. For example, Roman wooden, clay and stone piping systems most often used a compression joint by forcing the branch pipe into a hole cut in the main run pipe. In the early centuries, when the did not create a serious safety problem.

With the industrial revolution and greater use of steam creating higher temperatures and pressures, the industry began to experience more safety problems. In fact, in the late 1800's and early 1900's, a major cause of industrial accidents could be attributed to these factors.

Annual deaths were on the order of 50,000/year and injuries were on the order of 2,000,000/year. This was, of course, intolerable. At this time the ASME was a new organization and it began the task of writing the codes and standards so that there would be a defined safe way to design and build the boilers and piping systems.

This discussion will be limited to 90° or tee type intersections. Fundamentally, there is no difference from the angle type intersection typified by a lateral. Some of the computations are somewhat more complicated but the principles are the same.

Until the 1930's, there were three main ways to make a 90° tee type intersection.

1. A pipe to pipe intersection. This is still applicable for low pressure, low temperature situations where the pipes themselves are self reinforcing. It was the growth in temperature and pressures that made this intersection less and less safe.

2. A pipe to pipe intersection with some kind of reinforcing pad. As the ASME began to address the safety problems, they developed rules for the amount of reinforcement that was required to make the intersection a safe one. Today, area reinforcement calculations are found in B31.3 Paragraph 304.3.3. This method is still used in many applications, even though it is very labor intensive and, therefore, costly.

3. A tee type fitting. This simplified the labor of installation as the intersection was made a part of the tee and the installer then only had to make three girth welds. At this time, the people who were writing the codes included standards for lengths and heights of these tees. They also included ratings and testing requirements in the precursors of today's B16-9 and B16-11. These standards require the manufacturer of the tee provide proof in some acceptable manner that it was at least as strong as the pipe to which it would be welded.

In the 1930's, Bonney invented and patented the integrally reinforced branch outlet fitting with trade names for their products as Weldolet, Sockolet and Thredolet. This invention was simply a connection which was welded between the run pipe and the branch pipe designed to totally restore the full strength to the run pipe weakened by the hole cut in it to receive the branch pipe. This invention included several cost saving features over tees and reinforcement pad construction.

1. With the branch outlet fitting, the strength enhancing features of the pad were made integral to the fitting. This eliminated the extra cutting and forming of a pad and it also eliminated the extra welding and testing of the pad.

2. As related to straight tees, the branch outlet eliminates or saves one weld. Additional welding savings are realized when the branch outlet fitting replaces a reduction tee.

In later years when the Bonney patents expired, several manufacturers began to make integrally reinforced branch outlet fittings. In many cases, these manufactures attempted to copy the Bonney design but not always dimension for dimension. In the early 1970's, WFI entered the market with a new and improved design which had both a different shape than the Bonney branch outlet fittings and also met all the requirements of the B31.3 code. These differences in shape have led to a great deal of confusion in the industry.

We are constantly asked, how can I tell if a branch outlet fitting meets code by simply looking at its shape? The answer is that you can't. Shape defines the outside, not the structural integrity.

You must understand that there are several sections in the code that define the minimum safe way to design, build and test branch outlet fittings. It is incumbent on the manufacturer to provide the end user with proof that he has indeed designed and manufactured the branch outlet fitting in accordance with code. If the manufacturer cannot provide this proof, his branch outlet fitting cannot be considered to be code worthy.

The ASME B31.3 Code, as it was developed, gives direction to manufacturers as to what they must do to make an integrally reinforced branch outlet fitting meet code. Let it be clear, that the purpose of this paper is not to instruct you how to design a branch outlet fitting, but rather, what you should look for to determine if the manufacturer has provided you with a code worthy branch outlet fitting. Given that the code requirements may be met by more than one design, it is important that you understand the differences in these designs so that you can choose the best possible design for your application.

There are basically two ways branch outlet fittings can be designed and manufactured to meet the requirements of the B31.3 Code.

The first method is known as full area replacement The most well known and most commonly used method for weld fittings is found in Paragraph 304.3.3 of the B31.3 Code. This technique is required for those situations where one wants to use pad type reinforcement, but these rules can be used for branch outlet fittings. I won't go into the detail of how full area replacement is computed for a branch outlet fitting other than to say that the volume of metal required for pressure which is removed from the run pipe must be built back into the branch outlet fitting within a certain predetermined area. The method of computation is clearly defined in Paragraph 304.3.3.

The problem with branch outlet fittings being designed to these rules is that they become non standard and specific to a given set of process conditions and material. The special design is appropriate in unusual or very special conditions. Other sections of the ASME Codes, mainly Section I & VIII, limit you to area replacement for general useage.

The second method, and most commonly used by branch outlet fitting manufacturers who design and manufacturer to Code, is found in Paragraphs 304.7.2 and 306.1.3. These paragraphs describe the various testing methods to which a branch outlet fitting must be subjected to be determined as code worthy.

Basically these tests, as defined in Paragraphs 304.7.2 and 306.1.3, state that branch outlet fittings welded into a piping assembly must be hydrostatically tested at the rated pressure of the pipes in the assembly. If failure occurs outside the weld zone in either the run or the branch pipe at a pressure above the original pressure retention of the pipes, the branch outlet fitting is acceptable.

Paragraph 306.1.3 specifically states "Proprietary welding outlet branch fittings which have been design proof tested successfully as prescribed in ASME B16.9 may be used within their prescribed ratings".

Paragraph 304.7.2 is a general paragraph that allows such things as Section VIII, Division 2 analysis, proof or burst tests, finite element analysis and extensive direct comparison.

The above paragraphs require that manufacturers prove their fittings by one or more of the following means and with the noted limitations.

1. Burst or proof tests of an adequate range of fittings to cover all sizes and types of fittings offered by the manufacturer. That proof should include tangible and demonstrable proof that the untested fitting sizes:

a. Have similar geometry in the acceptable ranges for the applicable tests.

b. Have a manufacturing method that assures that the process of manufacture repeats his geometry on a consistent basis.

c. Have available for inspection the documentation of the tests and their results.

d. Have evidence of the consistency of the design process based on the geometry used in the test range.

2. A full set of mathematical analysis of their design (in accordance with the precepts of Section VIII, Division 2) and a detailed stress analysis (for example, finite element analysis). It shall show that the fittings comply with the appropriate allowable stress limits and provide sufficient reinforcement to reinstate the original strength of the pipe or vessel.

a. Analogous evidence of subsequent design and manufacture as outlined in "1" (a, b, c, d) above.

Additionally, Paragraph 304.7.2 allows for:

1. Calculation sets showing that each of their fittings has sufficient metal within the reinforcement zone to replace the metal as required by the rules of Paragraph 304.3.3.

a. Note this will require calculation sheets for every size and schedule combination (at a minimum). It must address the differences in the allowable stress differences as materials change. This means it should include a calculation for every temperature pressure combination of every material offered by that manufacturer.

2. A set of extensive use comparisons. These must include geometry, operating and design conditions, material compatibility, and length in service. The set, also, must cover the range and type of fittings in the manufacturers scope of supply.

WFI has used all of the methods in many combinations. We currently have some 29 Burst Tests in our on going test program. They are summarized in our Engineering Data Book. The original documents are stored at our facility. These are supplemented by several finite element analysis and the capability to do in-house finite element analysis.

In addition to the above, we have in-house capability to do area replacement calculations for those instances where the customer specifications and/or code requirements do not recognize the applicability of the above procedures.

It is important to note that the MSS, as well as the Code, imply the proprietary nature of the fitting by not specifying the OD or the shape of the fitting. In short, they recognize that branch outlet fittings are engineered products which through successful proof testing allows them to be constructed in various shapes. In other words, unlike flanges, tees elbows, etc. the Branch Outlet Fittings do not have to look alike - they just have to perform alike.

At this time, I would like to identify dimensions which should be standard in all branch connection fittings. The "A" Dimension, which is the distance from the crotch of the fitting to the top of the branch side, is found in MSS-SP-97. This dimension should be the same for all manufacturers fittings. In addition, the branch weld bevel should be designed to B16.25 and the ID of the fitting should match the branch schedule.

So far we have only been talking about pressure loads. The loads placed on branch connections externally are equally as important as the pressure loads. In fact, I submit that most failures in the field come from external loads rather than pressure loads. I hasten to point out that this conclusion excludes corrosion or similar aging factors, but it does indicate that pressure considerations are not the only ones. They may not be the determining factor in system life, but B31.3 does require the system designer to consider these loads in his analysis.

Let's talk a few minutes about external loads which can result in fatigue. Stress intensification has an effect on branch connections. I talked earlier about how the industrial revolution with higher temperatures and pressures focused attention on piping failures. As time progressed and pressure design became consistent and safe, it became evident that external loads were creating more fatigue failures in branch connections than pressure.

Recognizing this, stress intensification factors were derived from experimental work done several years ago by Tube Turns under the direction of A.R.C. Markl. Several papers and research exist in that field since and before the Markl (Tube Turns) work. Essentially, an SIF is the predicted (or measured) increase in stress over what one would expect to see in a simple (code acceptable) girth butt-weld under the same external load. Their use is to consider fatigue, as well as pressure, in branch connection designs.

B31.3 Appendix D sets out formulae to develop SIF's for various configurations including welded branch connections. The techniques of determining SIF's is not an exact science Most of the literature and experimentation points to the relative difficulty in determining accurate SIF's. WRC Bulletin 329 by E. C. Rodabaugh (entitled, "Accuracy of Stress Intensification Factors for Branch Connections") is an excellent summary of the known problems and suggests solutions to address those problems.

WFI has performed extensive fatigue analysis of its branch connections in accordance with B31.3 Appendix D and this information is also published in our Engineering Data Book. This is extremely important information to the piping designer in his design of a piping system and it is amazing to us how infrequently this information is requested. One must question how much depth of consideration is being given to fatigue analysis in piping systems and in particular branch connections.

As we have said, fatigue is a most complex subject and is subject to multiple considerations. Tests conducted by WFI in concert with the Welding Research Council and outside experts have shown that weld configuration has significant effect on the safety and stress intensification of fittings in fatigue situations.

In a soon to be published WRC Bulletin that discusses the "Effects of Weld Metal Profile on the Fatigue life of Integrally Reinforced Weld-on Fittings", one of the major conclusions is that the weld profile has a major effect on the fatigue life. While this points out the importance of the weld itself, it placed increased emphasis on the weld preparation and its importance in the safety performance of the fitting. That paper was recently presented in an international symposium in Orlando, Florida. It will become a Weld Research Council Bulletin in the near future. A second half of that bulletin will discuss the tests that are required to prove a SIF of a particular design. Again, those tests have been conducted with the welds out to the first bevel with a proper cap weld (a full penetration groove weld). The results of the test show that the smoothness of the welds has a direct correlation with stress (i.e., smoother is better).

B31.3 recently published an interpretation (11-10) which clearly dictates that the attachment weld for an integrally reinforced branch connection must be a full penetration weld. It refers to the wording in Paragraph 328.5.4 (d). As in all cases regarding code compliance, the code is the final arbiter.

In addition to everything we have talked about thus far, it is extremely important to insure the end user that the product will meet all the material specifications and quality requirements of the ASTM product form that defines it.

The sticker in this area is how do you know what the material is when you get it. Recent experience in buying flanges from China would tell you that just the stamping of an ASTM product form on the component would not assure that.

Any one who has been in the purchasing and supply business can tell a tale of similar woe to the Chineese problem. How do you assure yourself that you are getting what you want? The surest way is to have a source of components that is trustworthy and has the capability of proving their materials. Unfortunately, there are far too many copy machines and "cut and paste" masters in this world to just believe a copy of paper.

There is no substitute for careful analysis of material as well as documentation.

This is one area where quality assurance programs can help. WFI has held a Nuclear Quality Certificate for many years and all of our operations are run in accordance with this certificate. ISO 9000 is a program that does for the commercial world what the QSC's do in the Nuclear world. The ASME has recognized the validity of such a program and is in the process of becoming a certifying agency for ISO 9000 programs. WFI is on a 1994 end pace to incorporate the ISO 9000 program into our quality assurance arsenal. We look forward to others having to hold their toes to the same kinds of lines that we have been meeting.

Now, I would like to briefly point out to you the salient cost saving features of the WFI straight bore branch connection, PIPET®, as compared to our many competitor's taper bore design.

A detailed explanation and description of the WFI branch outlet fitting, PIPET®, is found in the WFI brochure entitled "The Most Innovative Integrally Reinforced Branch Connections-Pipets®... Straight Bore Branch Connections By WFI".

The brochure demonstrates and discusses why WFI Pipets® clearly have cost saving advantages over the conventional taper bore design of other manufacturers because they:

· Consolidate over a greater number of run pipe sizes which can reduce a stocking locations inventory
by more than 50%.
Have a smaller weld circumference area, thus reducing weld installation time on the average by more than 20%.
Are easier and faster to grind the back side of the root pass, further reducing installation time.
Weigh less, thereby making it possible for the piping design engineer to design and build a lighter and less
costly piping system.
Meet all the requirements of the applicable piping codes and standards.


What then is the conclusion that I suggest that you draw from these discussions?

They are as follows:

1. Branch outlet fittings are one of the most economical ways to integrally reinforce a branch connection in a piping system.

2. Branch outlet fittings are engineered products whose shape and outside dimension are determined through testing procedures as established by ASME B31.3.

3. There are basically only two ways the end user of a branch out fitting can be assured that the product meets code:

a. The manufacturer must provide pressure test data to demonstrate that the product has been tested in accordance with Code.
b. In the absence of pressure test data, the manufacturer must provide area calculations for each fitting sold to the end user.

4. Stress intensification factors are extremely important and should be known by the end user so that he can be assured the piping system is properly constructed and safe.

a. The manufacturer should have verification this his fitting has an SIF =/< code suggested.

b. Weld installation and weld profile greatly effect stress intensification factors.

5. You can not safely approve a manufacturer that does not have good quality control and good material control. Furthermore, that manufacturer should have effective control over his sources of supply for services. It goes without saying that if they have quality control, they will control the in-house manufacturing process.

6. The unique engineering and design features of the WFI branch outlet fitting, PIPET®, are superior to and have many cost saving advantages over the conventional taper bore branch outlet branch fittings.

The above is WFI Technical Paper, WFI,Houston, TX

Hello,

By the way, although it is slightly off topic you might want to look at this Standard:

SP-97-1995, $35.00
Integrally Reinforced Forged Branch Outley Fittings -- Socket Welding, Threaded and Buttwelding Ends

This MSS Standard Practice covers essential dimensions, finish, tolerances, testing, marking, material and minimum strength requirements for 90 degree integrally reinforced forged branch outlet fittings of buttwelding, socket welding and threaded types.

Go to this site:

http://www.normas.com/cgi-bin/search/search.cgi?q=fitting&Submit=go%21

Regards, John