Flange Connections 2

[GemmellG]

Working on assembling OTSG c/w convection & radiant sections. Project manager has requested the crossover tubing that connects both sections to be flange connections. This tubing fall within the ASME Section 1 rules (Boiler Proper). Is there any limitations or restrictions regarding the use of flanges in the code.

 

[LCeballos]

You must to follow rules according ASME Section I, as per:

PG-9; PG-11; and specifically PG-59 (PG-59.1.1.2)

Regards,

Luis C.

 

[davefitz]

I am facing a similar problem- replacing a dissimilar metal weld with a flanged connection at the outlet of a once thru cooler in a OTSG ( Alstom HRSG).

To use a standard 2500# flange, we needed to use 10 yrs of operating data from 14 duplicate units to justify de-rating the design temperature to a value that would allow a standard 2500# flange ( F91- 316H). Additional QC specs were addended to the SA182 spec to address F91 issues ( cooling rate followign normalization, hardness test of each flange )and 316 H "stress relaxation cracking" issues ( certified SA182 heat treatment record, grain size larger than astm 3.5) . Although others recommend use of Nimonic 80A bolting, asme section II does not provide allowable stresses for that material, so we will specify use of inconel alloy 718 SB 637 N07718 to meet code rules. Belleville springs used to address differential thermal expansion issues . It remains unclear if a standard 16.5 flange needs to also meet the external bending moment relationships defined in section VIII div 1 app 2, but we are now calculating that detail .

Section I allows use of flanges per B16.5 or designed by asme sect VIII using materials defined in section II.We wil file a asme sect I form P3A for each flange pair.

An alternative is to obtain a custom flange designed using finite element methods as section VIII div 2- yet being evaluated.

 

[ricklts]

You may want to consider a joint design other than a conventional ANSI flanged connection. I won't make this a sales pitch, but there are several manufacturers of alternate flanges (greatest difference is the seal design) or hub/clamp configurations, which are code compliant, and have histories of sealing successfully most difficult applications.

Rick

 

[davefitz]

rickits:
So far, I have only found one supplier that advertises that option- we are considering a custom 7500# flange by Vector , designed using finite element method per the design by analyisis rules of asme sect VIII div 2.

If you can advise a list of other such vendors, please advise.The others I have contacted will fabricate, but not design the flange.

Thanks

 

[ricklts]

davefitz,

I work for such a company, but don't want to make this a sales pitch on the forum. Try looking at

http://www.ltsenergy.com,

under the 'Tech Library' tab. You will see compact flanges and hub/clamp connectors, both of which are ASME and API compliant.

 

[saplanti]

As Davefitz indicated, there are a lot of restrictions on the use the flange connections in that area. The issue with material of the bolts is one side, the leak tightness is the most important one. You are going to install the flange at ambient temperature and it will work under the combustion exhaust fluid with very high temperature. Corrosion is another issue. You will not be able to control the thermal expansion of the bolts and you cannot tight them either during operation. Using spring washers are not solution since the washers are going to be soften and loose the spring action at that temperature.

Similar type application was asked me at around 6 years ago for the the clamped flange connections which are very proven at low temperature especially in marine applications. At the end, we recommended them to protect the clamped flange connection against the high temperature exhaust fluid and control the temperature of the flange and bolts. They were after quick release connection somehow, I cannot remember the exact details now.

Hope it helps

ibrahim Demir

 

[ricklts]

splanti,

True, but in the initial assembly make-up, bolt loads are calculated to provide the necessary loading required to achieve leak-free operation at the full range of temperatures/pressure/external loads. Too often, designers fail to realize that the ASME allowable stresses in bolting materials are mis-interpreted. The design allowable temperatures contained therein are based on bolt stresses at 25% of the Ys of the bolting materials, not the actual bolt stresses applied to individual bolted joints. These stresses are commonly in the 45% to 65% Ys range, and even as high as 90% in some instances. In most cases, I have cautioned that typical high temperture bolting be limited as follows: B7 @ 400 Deg. F, B16 @ 600 Deg. F, changing to higher strength materials above that.

The flange assembly, including bolts, seals, and the flanges themselves must have sufficient preload capability to withstand all of the design conditions. In many cases of thermal transients or external loads, additional bolt loads my be required. This is the reason that a one-load-fits-all approach often fails. The responsible engineer must account for all of these conditions before approving the specific assembly procedures for such flanged joints.

As for the hub/clamp connections, if the joints are API style with BX or RX ring gaskets, these joints are extremely prone to problems if there is any excessive side loads or thermal shocks. The gaskets are not designed to accomodate any movement in the joint due to these elements. These gaskets are plastically deformed in a specific ring groove on initial make-up, and will not relialby reseat themselves if movement from thermal or external loads occurs. The other similar connections, the 'Grayloc' style from Oceaneering and LTS Energy, can and do accept such movement and are leak proof in most cases. There are 'quick release' designs available to suit most applications for topsides, subsea, and petrochemical applications.

This same seal is used by most of these specialty manufacturers in a what is commonly called a 'Compact Flange'. These designs are currently in use in larger sizes - up to 42" - and pressures - up to 30K psi for ASME and API applications.

 

[GemmellG]

Welding P4 to P4 socket welds that do not require PWHT as-per B31.1 I plan to use a WPS that has PWHT thickness range of WPS is 3/16" to 8" Thickness of piping is sch 80.

 

[ricklts]

GemmellG,

While not a fan of SW'ed connections in high energy piping, in smaller sizes they do offer some benefits. If you are in the 3" (75mm) or larger nominal piping sizes, you may want to re-evaluate the use of SW flanges and fittings, primarily due to external load reactions due to thermal expansion/contractions. You never did state design conditions - ANSI class, etc.

 

[davefitz]

As a follow-up sect I PG11.1.1 provides a great deal of flexibility if the flange mfr can certify the he has designed + fabricated acccording to his corp. standards, using material defined in sect II, without welding, and certifies that it will meet the defined design conditions . This implies the flange mfr provide both design + fabrication . The "custom flange", designed according to the rules of sect VIII , can then be considered a standard component and not be saddled with the other documentation ( mill certs, P4 forms, stamping) issues.

Also, the 2010 editon of section I seems to have lost all its footnotes- go back to 2007 edition to obtain the footnotes that are referenced.

 

[ricklts]

davefitz,

I've never run across that section of the code before, and will want to take a look into it. However, I believe the intent of the code is to ensure that all design precepts/requirements for the complete vessel assembly are in compliance with applicable codes for the vessel and all connections, be they standard designs or custom.

As said previously, there are any number of organizations that provide fully qualified/proven/documented/designed/FEA'd custom connections where conventional ANSI/ASME/API designs are not suitable for any number of reasons. The situation you describe in your first post would seem to be one of those circumstances at which those firms excel.

 

[Kiwi2671]

GemmellG,
Not sure I have read your last post correctly but you do realise you cannot use a WPS qualified with PWHT to weld something that will not have PWHT ?
Cheers,
Kiwi

 

[davefitz]

Rickits,

I'm on board with your appraisal, but in section I applications, one either needs to certify the design with an "S" stamp or would need to use PG-11.1.1 and certify that the design meets the flange mfr standards, exact wording per code and associated footnotes. Flange mfrs with an "S" stamp seem to be a rare breed. One would presume the mfr standards include meeting sect VIII rules for design using sect II materials + properties, and due dilegence would imply confirming the mfr's desing stds and QC system.

 

[saplanti]

ricklts,

Your understanding of flange connection is correct but ignoring basic papers that the flange connection section in the code was created from. In the papers the fluid was inside the pipe and outside temperature was always less than inside, therefore the slight temperature difference between flange and bolt is used in faver of the leak tightness, ultimately the bolt temperature was going to be the temperature of the flange and the tightness was still provided by the preload.

Who garanties that the bolt temperature will not exceed the temperature of the flange since the flange is cooled by the steam and the bolt was heated by the exhaust fluid that is in a lot higher temperature than the steam, and leak tightness will not fail. If you think the preload will be sufficient for any kind of themperature change on the bolt I cannot say anything. The differential thermal expansion cannot be solved by increasing the number of bolts either.

I am not sure if you are discussing the issue after the implementation or not. But this kind of connections are prone to leak failure if the temperatures is not controlled on the connection and corrosion faliure if exposed to the corrosive boiler exhaust gases.

Good luck

Ibrahim Demir