bolting cadmium galv oversize

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For the past ten years I have been applying the coatings that have been used on topsides, coastal regions and pipelines. For the past three years I have been a Technical Speaker, Expert Witness, and Writer for NACE, ASTM and more recently API. Currently, I am working on the science behind ASTM, NACE and API in sub- committees and how they affect our industry when referred to as normal practice and normative reference. This is important, because normative references and Standards are by which Oil Companies, OEM, and Engineering Firms use to justify their Coating Specifications. Getting back to the importance of fastener coatings. We have been in a RACE with corrosion, ever since we learned how to stave it off with cathodic prevention and oxygen depletion. A couple of decades ago, cadmium was king, but received very unpopular publicity, due to it being toxic in nature. So we started looking for other solutions to extend the life of our fasteners. Our first choice was Hot Dip Galvanizing (ASTM A 325 & ASTM A 563) as it was already being used in the utilities and was easily accessible. This was when we realized one important issue in pressure bolting. The application of the LOAD applied in the form of torque made Hot Dip Galvanized fasteners a terrible application. We tried lubricants, but none worked. PTFE was looking for new applications other than frying pans at the time, so we used it as a dry lubricant and it worked. We also noticed that the combination of systems gave a higher resistance to corrosion, which meant we could extend the lifecycle and recoup a better return on investment to projects. Is it by mistake, or is it by design? In the race to bring equity out of a commodity we have over looked a few rules. Armed and Ready to Blow! Ian MacMoy February 6, 2015 The Tensile time bomb! Tensile vs. Shear……… Page 3 Pressure loss has been the detonator of recent catastrophes all over the world. Page 7 Two wrongs don´t make it right It just make it “normal practice” Page 9 Author: Ian MacMoy Product Design Specialist/ NACE ASTM API [email protected]

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Armed and Ready to Blow

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Page 1: Bolting Cadmium Galv Oversize

For the past ten years I have been applying the coatings that have been used on topsides, coastal regions and pipelines. For the past three years I have been a Technical Speaker, Expert Witness, and Writer for NACE, ASTM and more recently API.

Currently, I am working on the science behind ASTM, NACE and API in sub-committees and how they affect our industry when referred to as normal practice and normative reference. This is important, because normative references and Standards are by which Oil Companies, OEM, and Engineering Firms use to justify their Coating Specifications. Getting back to the importance of fastener coatings. We have been in a RACE with corrosion, ever since we learned how to stave it off with cathodic prevention and oxygen depletion. A couple of decades ago, cadmium was king, but received very unpopular publicity, due to it being toxic in nature. So we started looking for other solutions to extend the life of our fasteners. Our first choice was Hot Dip Galvanizing (ASTM A 325 & ASTM A 563) as it was already being used in the utilities and was easily accessible. This was when we realized one important issue in pressure bolting. The application of the LOAD applied in the form of torque made Hot Dip Galvanized fasteners a terrible application. We tried lubricants, but none worked. PTFE was looking for new applications other than frying pans at the time, so we used it as a dry lubricant and it worked. We also noticed that the combination of systems gave a higher resistance to corrosion, which meant we could extend the lifecycle and recoup a better return on investment to projects.

Is it by mistake, or is it by design? Is it by mistake, or is it by design?

In the race to bring equity out of a commodity we have over looked a few rules.

Armed and Ready to Blow!

Ian MacMoy February 6, 2015

The Tensile time bomb!

Tensile vs. Shear………

Page 3

Pressure loss has been the detonator of recent catastrophes all over the world.

Page 7

Two wrongs don´t make it right

It just make it “normal practice” practice”

Page 9

Author: Ian MacMoy Product Design Specialist/ NACE ASTM API [email protected]

Page 2: Bolting Cadmium Galv Oversize

4.3 Materials and Dimensions 4.3.1 The following bolting material grades are covered by this standard: — ASTM A193 Grades B7 and B7M; — ASTM A194 Grades 2H, 4, 7, 2HM and 7M; — ASTM A320 Grades L7, L7M, and L43; — ASTM A540 Grades B22 and B23.

4.3.2 All requirements of the referenced ASTM specifications shall be met except as modified by this standard. In the case of conflict between the requirements of referenced specifications and this standard, the requirements of this standard shall apply.

4.3.3 Oversizing of nut threads or under sizing of bolt threads is not permissible.

1

The Hot Dip process is difficult to control and the thickness varied quite a bit. We began using zinc plating and kept the PTFE topcoat. This gave us a 2-year lifecycle we could work with. The industry immediately saw the benefits of extending the maintenance intervals and eliminating the down time. But could we go to five years? That way we could combine maintenance checks on fasteners with pumps and valves. A new player was in the works from the automotive industry, and aluminum-ceramics (ASTM F1428) could provide the 5 years, as long as we kept the topcoat of PTFE for lubricity to apply the needed torque to achieve the load. So we kept oversizing the nut threads to accommodate this new system. Life was great! I have been applying ceramics for the last 6 years and writing and co-writing coating specifications for the past three years. I always have had a license to apply PTFEs, and aluminum ceramics and having that, made it easy to be approved as a vendor. It was not until API released 20E “Alloy and Carbon Steel Bolting for Use in the Petroleum and Natural Gas Industries”1 which standardized bolt manufacturing that I realized that there was something I missed. It states in 4.3.3 and in section 5.10.1 that over sized nuts would not be permitted, in accordance with ANSI/ASME B1.1.

API 20E Section 4.3.3 (Alloy and Carbon Steel Bolting for Use in the Petroleum and Natural Gas Industries)

2

Now why is this a problem if NACE International clearly states in TG 148 the following:

“Over tapping of the nut threads is a viable option to prevent make-up problems such as galling, seizing, fretting, and other thread damage. When the total dry film thickness (DFT) of the coating system is >0.75 mils (18 µm), over tapping of the nuts is a normal practice to prevent make-up problems.”2 As defined by TG 148/NACE.

If we go back to Hot Dipped Galvanizing on bolting (ASTM A 325 & ASTM A 563) and look at the scope, to understand it’s purpose: “The Bolts are intended for use in structural connections” 3 and “nuts for general structural”4. For pressure bolting, the industry also came up with ASTM A193 and A194. The scope of the standard helps us understand it’s purpose: “Steel bolting for pressure vessels, valves, flanges, and fittings for high temperature and high pressure service”5, “These nuts are intended for high-pressure or high temperature service, or both”6. “For this type of service, platings (zinc and cadmium) where considered designs in the tolerances of the threads for corrosion protection. This is the bolting the petrochemical industry refers to in standards like API 6A7 and API 20E8 from the American Petroleum Institute.

Page 3: Bolting Cadmium Galv Oversize

“over sizing was never allowed, ANSI/ASME B1.1 clearly states the measurements of allowances…”

– Tom Goin

We need to understand there is a major difference between structural bolting that works with the shearing of the shaft and pressure bolting that works with tension on the treads; I am quoting a book to better illustrate the difference.

“The distinction between tensile and shear joints is important, because the two types differ in the way they respond to load, the ways in which they fail, the ways in which they are assembled, etc. In general, the tensile joint is the more complex of the two”. 9

“Bolted joints are classified by the service loads placed on them. If those loads-forces-are applied in a direction more or less parallel to the axis of the bolts, as in the upper sketch, here, the joint is called a tensile or tension joint. If the line of action of the forces is essentially perpendicular to the axes of the bolts, as in the lower sketch, the joint is called a shear joint.” 9

Page 4: Bolting Cadmium Galv Oversize

I have to tell you that this was something I did not want to hear. As much as I understood the importance of actual science over normative reference, it was still something I had come to know as a normal practice. President Ronald Regan said, “Trust but verify” was something he learned from doing business with the Russians. Now Tom Goin is not the Russians, but I did want to get another opinion before everything I had once known was turned upside down. So I went to see Jerry Longmire who is the Head Chair of API Supply Chain 20. He had helped author the standard and he stated, “Not only was oversizing never allowed, but that oversizing nuts was the cause of 70% of the failures in ASTM A194 “Proof Load Tests”. I also learned, that is when it has been carried out correctly, most if not all of the “Proof Load Tests” are being done by the manufacturer, not the distributor, who oversized the nut by 10 mils (250 microns) to accommodate the coating thickness.

After learning all this I went to see the sub-committee chair of API 20E, Mr. Tom Goin. My question to him was, why are you not allowing oversizing any more? He stated, “over sizing was never allowed, ANSI/ASME B1.1 clearly states the measurements of allowances between the internal and external thread pitch. By the way API 6A does not allow it either; it has to do with tensile strength and equipment under pressure.”10 My response was, “ASTM A325 and ASTM A563 allow it!” ASTM A563 allows, “Nuts… shall be tapped oversize after coating, to the minimum and maximum thread dimensions in table 5”. The fact is that these two standards are for structural bolting and do NOT apply to pressure bolting ASTM A193 and A194, remember: “The distinction between tensile and shear joints is important, because the two types differ in the way they respond to load, and the ways in which they fail…”11

Page 5: Bolting Cadmium Galv Oversize

A series of newsworthy events, many of them tragic, have made us realize that the threaded fastener still plays a major role in our lives.

Oil drilling platforms have tipped over, airplane engines have failed, roofs have collapsed, and astronauts have died because of bolted joint failures.

The Nuclear Regulatory Commission has declared “bolting” to be “unresolved generic safety issue with number one priority.”

- John H. Brickford

I called 26 fastener distributors and this is what they told me; that either they have never heard of this test, their POs do not call for this test, or they have it done by the manufacturer before the modifications are done. Meaning the modified nuts which do not comply with ASTM A194 and ASME B1.1 are being installed in the field without ever being subjected to the pressure qualifying tests. I was scared to hear this as ASTM A194 clearly states, “All nuts shall be capable of withstanding the proof loads specified…”12 it also states “Modification of thread dimensions may result in loss of load carrying ability”13 Even ASTM A563 (HDG), clearly states that “Nuts hot dip or mechanically zinc coated in accordance to 4.7.2 or 4.7.3 shall be proof load tested after zinc coating and over tapping.” So what happens if you have a non-standard fastener? “Here the path becomes a little murky, but I will still give you a useful answer unless your need for accuracy and safety is critical” John H. Bickford 14

The nut depends on the first two threads of the engagement to hold 57% of the load. If the first thread shears the rest follow in a domino effect. The stress picture is not an attractive one since most of the load is on the first thread. If you look at the chart below the fall of the stress is not linear, it’s curved.

Page 6: Bolting Cadmium Galv Oversize

When you oversize you lose thread engagement.

Looking at the drawings below, the one on the left has full engagement of the threads and the force is transmitted through the nut to the bolt. The picture on the right shows an oversized nut, the force is concentrated on the peaks of the threads. When the whole thread pitch is not used the force is concentrated an plastic deformation occurs in the valley. This will start a chain reaction of failures. The joint will lose load through relaxation of the threads and begin to creep and therefore leak both pressure and containment. One of the offsets that occurs in the field is creep, which is the outcome of tensile strength loss from a consistent load, or multiple high low loads over time.

“A broken bolt is easier to detect than a strip thread, so we never want the threads to strip.”17

My question remained: we have never seen a failure; bolts don’t break from over sizing of the nut! So I did some research and found the amount of tension we can create in a bolt not only depends on the strength of its body but on the shear strength of its threads. We will want to be sure that the thread engagement is great enough to allow us to develop the full ultimate strength of the bolt. “What we do see is Poor Thread Engagement. If the bolt is undersized, or the nut oversized, thread contact areas will be less than those planned by the designer, and substantial plastic deformation may occur. Especially in gasketed joints where relaxation is substantial and can be as high as 80-100% lose of initial tension.” 18

“Fasteners that do not meet ANSI (ASME B1.1) specification are generally avoided.”19

Page 7: Bolting Cadmium Galv Oversize

This figure is a simplified view of the stress in a loaded joint.

There are two danger points where stress concentrates.

1. Where the head joins the body 2. The first thread to engage the nut

“I have been doing this for years and we have never had a failure.” My next question was, How much can oversizing of 10 mils affect the strength of the nut? I was impressed with what I found:

“If the pitch diameter of that bolt is 10 mils less than nominal, it will have less than half the rated strength; at 20 mils, it will have only a quarter of its rated strength…”15 “In my experience it may be necessary to over-tap more than 10 mils to allow for a ceramic coating thickness”

-William Eccles CEng FIMechE BSc PhD Bolt Science Limited

But we never undersize the bolt, we only oversize the nut; this is what I found:

“A similar loss of strength occurs if the pitch diameter of the nut is greater than nominal”, “Anything that reduces the amount of contact between male and female threads will affect the strength”.15 By the way ANSI B1.1 also states, “Standard internal threads provide no allowance for coating thickness.” 16

The gasket joint is sealed by applying load to the fasteners.

Not having a full thread engagement is failure in the making.

The threads have concentrated stress and plastic deformation will occur. The resulting deformation will release the load needed to maintain the seal of the joint.

This is common occurrence in the field associated with oversized nuts.

Pressure loss has been the detonator of recent catastrophes all over the world.

The Ticking Bomb: Creep Relaxation

Page 8: Bolting Cadmium Galv Oversize

It was Winston Churchill that said, “It may not be the best system, but it’s the best one we have so far.” That is how we see coatings and oversizing. We know there has to be something better, but this is the best solution we have come up with and the aluminum ceramic coating gives us our 5,000 salt spray hours. Any coating that requires over tapping in order to apply a coating’s optimal thickness should be avoided when tensile strength is accounted for as in ASTM A193 and A194 and ASME B1.1. Removing the substrate of a thread in a nut is changing the thread engagement needed to maintain the tension strength of the nut. Having written and helped write four aluminum filled ceramic coating specifications for major OEMs and in those specifications it states: oversizing as a viable means to accommodate coating thickness, has made me very aware of the definition of “normal practice”, which I now know is wrong. I am not a mechanical engineer; it was wrong of me to state oversizing even when it was known to be “normal practice” by the coating specifications and ASTM F1428 Section 5.4.1.-Sizing

ASTM F1428 statement to oversize in its application should not be treated as a normative reference and standardized. When working with pressure bolting ASTM A193 and A194, as well as ASME B1.1 shall be followed.

“We have been doing it this way for years… don’t rock the boat.”

-(You don´t want to know who said this)

5.4.1 Sizing--- The thickness of the coating is limited by the basic thread size. Where greater thickness is necessary, threads may be produced undersize or oversize (before coating) to accommodate the coating thickness, providing that the finished fastener (after coating) meets all specified mechanical properties, as agreed upon by the supplier and the purchaser.

as over sizing does here, You do not comply with the standards; you put the safety, health and environment around that system at risk. Once you introduce risk into the system, you become negligent for terms you define as

Page 9: Bolting Cadmium Galv Oversize

Conclusion:

When one ignores the mechanical engineering and science, as over sizing does, one does not comply with the standards; it puts the safety, health and environment around a system at risk. Once one introduces uncalculated risk into the system, one becomes negligent for terms that one defines as a “normal practice”. In Conclusion, NACE TG 148 should redefine its terminology for “normal practice” and clearly Specify oversizing as a de-rating of the fastener, and not to be used in pressure bolting. Then, outline the pressure bolting to follow the ASTM A193, ASTM A194 and ASME B1.1 as well as API 6A and 20E. It should also outline the importance of the “Proof Load Test” and its correct application and procedures. NACE International is here to provide guidance to the industry with actual science and lab testing, and provide technical task groups in order to further our knowledge and use of new technologies. I hope we are doing so today.

Page 10: Bolting Cadmium Galv Oversize

Footnotes and Biography:

1. Alloy and Carbon Steel Bolting for Use in the Petroleum and Natural Gas Industries API 20E American Petroleum Institute

2. NACE International Task Group 148 on Coatings and Methods of Protection for Threaded Fasteners Used with Structural Steel, Piping, and Equipment

3. ASTM A 325 Standard Specification for Structural Bolts, Steel, Heat Treated, 120/105 ksi Minimum Tensile Strength. Scope 1.2

4. ASTM A 563 Standard Specification for Carbon and Alloy Steel Nuts. Scope 1.1 5. ASTM A 193 Standard Specification for Alloy-Steel and Stainless Steel Bolting for High

Temperature or High Presssure Service and Other Special Purpose Applications. Scope 1.1 6. ASTM A 194 Standard Specification for Carbon and Alloy Nuts for Bolts for High Pressure

or High Temperature Service, or Both. Scope 1.1 7. Specification for Wellhead and Christmas Tree Equipment, American Petroleum Institute

6A 8. Alloy and Carbon Steel Bolting for Use in the Petroleum and Natural Gas Industries API

20E American Petroleum Institute 9. “An introduction to the design and behavior of bolted joints, third edition”, John H.

Bickford. Pg 4 Basic Concepts 10. Tom Goin, 20E Supply Chain Sub Committee Chairman at the American Petroleum

Institute. 11. “An introduction to the design and behavior of bolted joints, third edition”, John H.

Bickford. Pg 4 Basic Concepts 12. ASTM A 194-03b Standard Specification for Carbon and Alloy Nuts for Bolts for High

Pressure or High Temperature Service, or Both. Section 7.2.1 13. ASTM A 194-03b Standard Specification for Carbon and Alloy Nuts for Bolts for High

Pressure or High Temperature Service, or Both. Section S7.1 14. “An introduction to the design and behavior of bolted joints, third edition”, John H.

Bickford. Pg 28 Threads and Their Strength 15. “An introduction to the design and behavior of bolted joints, third edition”, John H.

Bickford. Pg 75 Threads and Their Strength 16. ASME B1.1 2003, Unified Screw Threads (UN and UNR Thread Forms) Sec. 7.6 17. “An introduction to the design and behavior of bolted joints, third edition”, John H.

Bickford. Pg 16 Stress and Strength Considerations 18. “An introduction to the design and behavior of bolted joints, third edition”, John H.

Bickford. Pg 197 Stress and Strength Considerations 19. NACE International Task Group 148 on Coatings and Methods of Protection for Threaded

Fasteners Used with Structural Steel, Piping, and Equipment pg 5 20. ASTM F 1428 Standard Specification for Aluminum Particle-Filled Basecoat/Organic or

Inorganic Topcoat, Corrosion Protective Coatings for Fasteners