Common Bolt Type for PED (no special temperature requirement or corrosion resistance) 1

[servobrake]

What is the common go-to bolting in the EU for PED vessels? Any recommended suppliers?

Under ASME ASTM A193 B7 is perhaps the most common material for bolting for pressure vessels where there are no special temperature or corrosion resistance requirements. It is widely available and inexpensive.

Our current bolt is ASTM A193 B7 UNC 1.5-6 x 12 inch heavy hex head. We go to great trouble getting them compliant to PED because PED has the 27J Charpy impact requirement and mill certs do not have this test. We end up paying %2000 for EN10204 3.2 certification and have a PMA in our certification paperwork.

We'd like to just buy 500 of whatever people in the EU would use, importing from EU is fine if the paperwork is PED. We can change to metric threads if that makes it easier.

 

[XL83NL]

Hi there. We do a lot of PED vessels for the EU, both under ASME code and EN 13445. The code has great influence in bolt material with respect to applicable standard (e.g. SA 193 or EN ISO 4017). However, stainless is stainless, so in that respect, it's just a matter of picking the right grade (e.g. B8 for ASME, 8.8 for EN 13445).

If B7 is an issue for charpy impact testing, which I doubt (we never had issues with formal PED compliance on that), go to L7 bolts, under SA320. They have specified impact properties (under SA 320 para 1.2 - and table 2), and are suitable for lower temperatures than B7 (which is were the impact requirement comes from). L7's are just as cheap, only slightly more expensive, but for small sizef flanges (say anything up to M24), it's a few percent.

We also coat all our studs & nuts using PTFE Xlyan 1070 coating, provided the max design temperature allows it (i.e. < 230 °C).

Changing to metric is something I wouldnt do; follow the appropriate bolting requirements from the applicable flange standard; so UNC or UN-8 for B16.5, metric for EN 1092-1. Dont mix that up, as the bolt root stress area is not interchangeable.

Suppliers - I can name a few, but only Dutch, and few abroad (Germany, UK).

 

[servobrake]

Thanks!
We are having a notified body do our PED conformity assessment (TUV Sud) our company's core competence isn't pressure vessels, but we need to PED certify a 3500psi 18.5 inch bore pneumatic actuator in our system.

The bolts hang us up because our notified body considers them pressure bearing and to them that means:
1. The bolts have to be impact tested to prove the 27J absorption
2. The impact test either has to be done by the manufacturer (not the distributor) and reported on an EN 10204 3.1 MTR, or we need to do a EN10204 3.2 certificate ($2000 charge)
3. The manufacturer has to either have an ISO9001 certificate where the competent body has an EU address, or a PED certificate.

I am having a lot of trouble buying bolts in the US that meet all these conditions, and it takes tons of time to jump through all the hoops. At this point it seems easier to figure out what an EU PED manufacturer would use and import a bunch of bolts.

It isn't that B7 is an issue for Charpy testing, they always easily pass. It is that it is so hard to satisfy the paperwork requirements.

The L7 idea is great. Then the mill cert will always have the impact testing.

Dutch, UK, German suppliers? Please tell me, and what is the grade that is similar to B7 (commonly used and inexpensive).

It is possible our notified body is telling us we need to jump through more hoops than really needed. For example we have 27 bolts on a flange, yet they consider each individual bolt a main pressure bearing part (failure compromises the overall integrity of the assembly) so the bolts shall have a certificate of specific product control. A bolt failure would not cause a system failure, but I can't tell if their interpretation is common or unusual.

 

[XL83NL]

I could comment on each and every question you have, and I’d be happy to do so, but I think you have another (easier) issue first. Based on your info, I don’t think your application falls under the PED.

Do you have a sketch and a more detailed description of your application? Is it part of an assembly? Is it a pneumatic actuator of a valve? Where are you located and where does the unit or item has to go to?

 

[servobrake]

Hi,

You can see a system photo at

http://www.seattlesafety.com/products/servosled-catapult-sled-systems/

The system accelerates a payload (such as a car body with dummies and airbags inside bolted to a guided platform) to the operator's acceleration vs. time curve. The payload is thousands of pounds and the g's as high as 100, so the force needed is as much as 800,000 pounds.

The cylinder labeled ServoSled on the side is the pneumatic actuator, filled with air up to 3500 psi. It has a rod that applies force to the platform.

You can't see it in the photo, but the g level is modulated with a very fast friction brake under the platform.

We are told that:
1. Our pneumatic actuator falls under the PED because it is fundamentally designed to hold pressure (the pressure stresses are not incidental)
2. The volume and pressure puts us in PED Category IV.

We are located in Washington state, and these labs are installed all over the world. Our understanding is that all installations in the EU require PED certification as part of ce, and unlike much of the ce certification we cannot self-certify for PED, a notified body has to certify the system conforms.

We tear out our hair at the difficulties getting the pneumatic actuator PED certified, to the point where we are considering having the entire pneumatic actuators made in the EU and shipped to us PED stamped.

 

[XL83NL]

I understand your frustation and all the questions you have. Dealing with the PED (the first time) can be somewhat tricky. We (the company I work for) have extensive experience with the PED, and all the (small unknown) details in it. As such we have also found (and paid for) the typical exceptions, which we now use as much as possible to our benefit. In the end, all the paperwork takes time, and NoBo's (short for notified bodies) are expensive.

Your application seems like something that could be considered an exception, i.e. outside the scope of the PED. Do you have a copy of the PED? Also make sure to have access to the PED guidelines, a Q&A type document given some useful insight into the scope of the PED, and how to deal with specific topics.

Look at chapter 1, article 1, item 2(j)(ii), and guidelines A-11 and A-19.

As an example, all the pumps and compressors we buy for the plants we built (also for the EU market), dont fall under the scope of the PED, for the pressure casing itself of the pump housing or compressor. If we have very big pump assemblies (more like a package unit) with intermediate piping, valves and vessels (e.g. dampeners), such piping, valves and vessels will fall under the scope of, but never the casing of the pump or the compressor.

You may have a point here. Talk to your NoBo.

 

[servobrake]

Thanks again.

PED Annex 1 Article 1 2.1.5 "Assemblies” means several pieces of pressure equipment assembled by a manufacturer to constitute an integrated and functional whole."

This is a reasonable description of our Pneumatic Actuator.

PED Annex 1 Article 1 2.1.5 "equipment comprising casings or machinery where the dimensioning, choice of material and manufacturing rules are based primarily on requirements for sufficient strength, rigidity and stability to meet the static and dynamic operational
effects or other operational characteristics and for which pressure is not a significant design factor."

Although the rod in the Pneumatic Actuator might fit this description, the barrel, flanges, end plates are all designed with pressure as a primary design factor.

Our notified body told us that we cannot consider an entire lab a single device, because it is built up of various sub-systems that are physically distinct. Therefore PED compliance is considered by each sub-system, similar to say, a power plant. It is not a single piece of equipment.

Talking with our notified body is frustrating. They seem to want to give the most severe and strict guidance. It is up to us to try to figure out if their guidance is in accordance with common practice. For example I just uploaded a picture of our pneumatic actuator

https://files.engineering.com/getfi...-4426-a6cc-7c0fca2081be&file=3MN_Actuator.png

in it you can see the bolts. I can see how big critical parts such as the barrels and flanges are Main Pressure Bearing Parts, a breach in any of them can fail the assembly as a whole. But the bolts? Very high redundancy. A single bolt failure would not even cause a leak. But when I made that argument they said they would ask their colleagues in Germany. They did, the answer is no.

I'm sure this is a settled issue, lots of pressure vessels have flanges attached with bolts. But I cannot find this addressed in the PED Guidance, and my googling didn't find anything. So we tear our hair out trying to find bolts with the right paperwork.

 

[XL83NL]

Does this actuator have moving internal parts? I still have my doubts if PED applies. Where is your NoBo situated? How experienced is he with the PED? You dont want to believe the sh*t we have dealt with NoBos thinking they know it all. In the end, you need to be able to know as much as they do, cause otherwise they may occasionally **&@$^ you ...
You may want to consider switching NoBo's.

The issue with the bolts being, or not being, main pressure bearing parts is a difficult one. It boils down to intepretation. See PED guideline G-08 (and G-06) for more guidance. There might be an escape here; if you can show, e.g. by calculation, that failure of 1 bolt doesnt result in sudden discharge, you may be good. However, guidelines are not legally bindiing, so NoBo's may ultaimtely waive whats in it. See page 1 of the PED guidelines.

I can understand the frustration you have when a NoBo tells you to do something, which doesnt seem right.

If there's anything else I can do to help, let me know.

 

[r6155]

Due that bolt is interchangeable the test temperature is at least as low as the intended service temperature and the bolting
is suitably marked to identify the reported test temperature. (see SA-320)

Regards
r6155

 

[servobrake]

Thanks for responding XL83NL!

Yes, it has an internal piston and rod that move. A picture that includes a cross-section is at

https://files.engineering.com/getfi...35f6-4caf-a090-2613d48e914e&file=Actuator.png

We are looking at changing our NoBo. So far the only US located PED NoBos I have found are TUV Sud and Intertek. Does anyone know of others?

I agree on the bolts. We could make a case. As you say in order to formulate a good case you need to know a lot about how the PED works. It seems there is no alternative to learning it ourselves unless we can find a PED knowledgeable consultant who can help us prepare an argument to present to the NoBo.

 

[servobrake]

Thanks for responding r6155!

Our temperature operating range is 10°C to 40°C.

Out problem is not meeting the temperature range. It is having paperwork for the bolts that satisfies our Notified Body. Do you know of a common bolting type used in Europe for PED pressure Vessels? Thanks.

 

[r6155]

servobrake
Sorry, I don´t know.

Regards
r6155

 

[servobrake]

Thanks

 

[XL83NL]

I was overthinking your application again. You would have a good case to switch NoBo, as I dont see how this would be considered a pressure vessel. Yes it does contain pressure, yes it needs to be designed to withstand that pressure, but so does e.g. a hydraulic cylinder, which is outside the PED scope. Given that it has a (moving) piston, I dont know of any leads in the PED, nor it's guidelines, that it's considered a pressure vessel as defined by the PED.

I can provide you with some NoBo's in the EU, but it wouldnt be of any use;
- in case you're right, which you hope to find out, they dont have to do any work, since it's outside scope PED. However, what you might want to do is still contact an experienced EU NoBO (I'd contact Lloyds Register Netherlands), have them verify your work, and have them make up a document stating the cylinder is outside the PED scope.
- in case the cylinder is deemed to fall under PED scope, a NoBo needs to come in to do some (paper)work; having a guy fly over from UE to USA or CA isnt worth the bucks.

However, one other aspect which may come into play is the Machine Directive, another EU directive. That ones a bit more trickier, but it usually doesnt require a NoBo; all the paperwork can be done by the manufacturer.

PS: OT again, here are some EU grades for A320 L7 bolts;

https://www.rodacciai.com/UPLOAD/datasheets/A320L7-L7M_A320L7-A320L7M-ENG.pdf.

PLease bear in mind however, that such EU grades may be the same on a chemical basis, but may differ in mechanical properties and/or testing. For example, they may not have guaranteed standard impact values equivalent to A320 L7 - that might be additionally specified.

 

[servobrake]

Thanks XL83NA,

I had the impression the reason hydraulic cylinders are easy is the incompressible fluid puts them in PED Category 1. In Category 1 the requirements for specific quality control documentation go away, as does the PED specific welding requirements. I have the impression that for Category 1 producing under ISO 9001 pretty much does the job.

The compressible fluid (air) and volume put us in Category 4 (if it is considered a pressure vessel, of course).

I'm happy to contact Lloyds NL, good suggestion.

Thanks for the Rodacciai citation. Would you in the Netherlands choose an ASTM bolt for use in a design? Wouldn't an American Standard bolt be inconvenient, a bolt to a European standard be easier to buy and probably cheaper?

For a PED design built in the EU, what bolt would be easiest to get in the Netherlands? (M39 or 1-1/2 inch, tensile/yield around 860/760MPa, temperature range 10°C-40°C , not stainless). If M39 is unusual we could use M36 or M42.

 

[XL83NL]

Whats your volume and design pressure? O wait, your volume is variable based on the psiton .... ah, you dont have a pressure vessel.

For NL applications, or any EU application, I would let the bolt material be decided by the design code. So if I have ASME VIII-1 design, Id take SA320 L7 bolts. If I use EN 13345, Id take 1.7225 bolts acc. EN 10269.

In general, we have had zero problems with getting American bolt grade material in metric sizes. M39 may not be a very common size, but at least its an 'EN 1092-1 size', so Im sure the suppliers will have it. Dont take M42, it's not a listed EN 1092-1 size. M36 is though:

Stokvis Trading is one supplier we have good contacts with, ohters are Metrik and BEA. All are Dutch. At your temperatures, Id have my bolts Xylan (PTFE) coated. At least Stokvis is familiar with such coating, the others I dont know of.

For a PED design built in the EU, what bolt would be easiest to get in the Netherlands? (M39 or 1-1/2 inch, tensile/yield around 860/760MPa, temperature range 10°C-40°C , not stainless). If M39 is unusual we could use M36 or M42.

Id go for SA320 L7 (w/ Gr 7 nuts). If impact testing isnt a requirement go for SA193 B7 (w/ SA194 2H nuts). I havent verified the mechanical values, but Im sure you can do this yourself.

 

[servobrake]

XL83NL, Tremendously helpful post and all the way along in this thread. Thanks.

 

[servobrake]

Perusing EN1515-4 (Part 4: Selection of bolting for equipment subject to the Pressure Equipment Directive 97/23/EC)

Table 3 Shows 8.8 per ISO 898-1 for -10°C - 300°C use.

ISO 898-1 gives tensile min of 830 and yield of 660 MPa.

Is 8.8 bolting common for PED vessels? What would be the reasons not to use in applicable operating temperature range?

 

[XL83NL]

Yes it is. Re the EN 1515-4 standard; I knew I had forgotten to mention/look a bit deeper. That’s the one used as a guide for EN13445 designed vessels. Be careful though that most materials don’t comply with ASME S8D1.

 

[servobrake]

"Be careful though that most materials don’t comply with ASME S8D1"

Yes, this at times causes a real problem. For example here in the US I have seen "ready-to-hone" seamless cold-drawn tube produced to ASTM A519, with DIN St52.3 chemistry specified (200mm bore 241mm OD). It has excellent mechanical properties and tolerances, but is not usable for ASME because ASTM A519 is not on the ASME Customary Materials List.

However we are told it can be used for PED provided we have the right mill certificates and we write a PMA, even though we are using ASME calculations as our design basis. Our NoBo has told us that using ASME calculation methods as the PED design basis does not limit us to materials on the ASME list.

Does this match your experience?