High strength bolting in marine environment

[rcchap]

I am replacing a large part of a compressed air system at a power plant that is in a coastal environment. The system is outdoors, and parts of it are near the plant discharge canal. We are replacing most of the carbon steel piping with 316L stainless steel due to the corrosion that has occurred both inside and outside the system. The environment near the plant discharge is extremely corrosive since the discharge waterway has a salt concentration that is higher than the ocean (due to evaporation of the warm water).

I have been trying to determine the best type of bolting to use for the flanged joints. I need to use a high strength bolt since I will be using sheet gaskets (Blue Gard 3000) that require a fairly high compressive stress required for a proper seal. Thus, I can't use B8M Class 1 (type 316) bolts. I have considered using B8M Class 2, but since they are strain hardened, I am concerned about stress corrosion cracking.

My other option would be Type 630 (17-4 PH) bolting, but I have not been able to find any information on how these bolts perform in a marine environment. I have concerns about this type of bolt since it doesn't contain any Mo like the 316 SS. I am not sure that a Type 632 bolt (w/ Mo) even exists. I have not been able to find any.

Should I use the 17-4 PH or B8M Class 2? Does anyone have any other recommendation for a high strength bolting material that would perform well in this marine environment?

 

[EdStainless]

What temperature is the piping? If it is above ambient I would suggest that you epoxy coat the outside of the piping to prevent external SCC.
There is marine grade bolting in both CuNi alloys and superduplex stainless.

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Plymouth Tube

 

[strider6]

Is you piping insulated? i suggest u to have a look at NACE SP0198 "SP0198-2010, Control of Corrosion Under Thermal Insulation and Fireproofing Materials—A Systems Approach
NEW IN 2010! " that gives guidelines and recomendations to prevent corrosion under insualtion.
As Ed said there could be some problem with SS 316 exposed to an enviroment with an high chlorides content. the 317 SS has higher resistance to marine atmosphere.

http://www.ssina.com/download_a_file/corrosionfinal.pdf

http://www.stainless-steel-world.net/pdf/11003.pdf

S

Corrosion & Rust Prevention Control

 

[rcchap]

Temps for most of the piping will typically be ambient (up to 95F in summer), but at some parts of the system may get in the 150-200F range for limited periods of time.

The piping will not insulated.

We are putting in about 1000 feet of new piping, so exotic piping alloys were not an option due to cost. The plant has decided to not paint the SS piping. Other 316 piping out there is holding up, although it isn't very shiny. I am hoping that the 316L grade does better in the HAZ. In any event, the stress in the piping is pretty low, so don't think SCC will be much of an issue.

It is the bolting that concerns me since the stresses will be much higher. I will need to torque to a bolt stress of 60 ksi.

Monel won't work because the tensile/yield strengths are too low.

I will look into 317, but I have a feeling that it will have mechanical properties similar to 316, which won't work because I need a high strength bolt.

17-4 PH is used for marine components, but it apparently has similar corrosion properties to 304. Does that eliminate this as an option?

I will look into duplex, but I have a feeling that they will be expensive. Is galvanic corrosion and issue with duplex and SS?

 

[rcchap]

Any thoughts on an A453 Grade 660 bolt? It has the necessary strength (85 ksi yield). Chemical requirements show it has a lot of Ni and Cr, and also has some Mo and Ti.

 

[EdStainless]

any reason that you are not looking at ATI2003 or a similar lean duplex alloy?
Price is similar to 316,
pitting resistance is just as good (if you pick the correct grade),
the welds will nearly match the bulk corrosion resistance,
the alloys have useful SCC resistance (much better than 317),
and with the higher strength you can reduce walls (20-30%) for the same pressure rating.

Today there is really no reason to use 316 unless you are over 600F. Use a duplex.

I used to buy cold formed and aged Monel K500 bolts.
17-4 has proven problematic for me. If there is any corrosion then SCC (or hydrogen) leads to failure.

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Plymouth Tube

 

[rcchap]

Ed, for the SCC failures of 17-4 PH bolts that you have seen, what condition were they (H900, H1100, etc)?

Last night, I found an EPRI tech report (1002792) that documents testing of 17-4 PH bolts in a marine environment with a stress of over 75% of yield. They found that the H900 condition is extremely susceptible to SCC in a marine environment (all H900 samples failed within a month). However only one of the six condition H975 bolts failed in 10 years of exposure. This implies age hardening at higher temps gives increased SCC resistance.

Is this research consistent with your experience with 17-4 PH bolts?

And to answer your question, there are numerous reasons we aren't using an exotic alloy for the piping. One of these reasons is the fact that the plant doesn't have weld procedures for that type of material, nor would they have any welders qualfied to do the welding because this material is not in ASME Section IX.

 

[EdStainless]

It was higher temp than 900F, the UTS was only about 175ksi, so maybe 950F??
The bolts failed by hydrogen embrittlement after suffering a very small amount of surface corrosion.

I have seen testing in oil field applications where H1150M (overaged) was the only condition that would survive.

I have seen people propose spraying the hardware with pure Zn before it is assembled. I can't find a reference that proves the effectiveness of this treatment.

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Plymouth Tube

 

[unclesyd]

Could you comeback with some sizes of your piping system?

It seems that your required bolt stress is high based on what I would expect to see for Blue Gard gaskets. For this type gasket material we use a bolt stress at its highest, 50,000.

Have you thought about a change in gasket material to lower the required bolt stress?

A lot of green and blue Teflon coated steel is being use in applications such as yours. There are some incidences of Nitronic 50 being used where a higher strength fastener is required.

I used 17/4 H1125 threaded rod to hold chain plates on an old fishing vessel. The service life has been 30+ yrs and still going.

 

[rcchap]

The piping will be 3", 4", and 6". The 3" piping will have 300# class flanges, and the 4" & 6" will use 150# class flanges.

I was going by the Garlock recommendations contained in their GSK 3:1 doc (available on their website). We are using 1/16" gaskets, and Garlock recommends a 3600 psi assembly stress. I didn't calculate it out, but on page C-43, they provide recommended torque values. Our bolts will be 5/8" and 3/4", and the tables give a preferred torque of 120 ft-lbs for 5/8" bolts, and 200 ft-lbs for 3/4" bolts. These are the 60 ksi stress values.

Even if I torqued to 50 ksi, I still couldn't use B8M with a yield of only 35 ksi (unless I used Class 2).

I am going for leak tight joints, which is why I am using BlueGard 3000 gaskets. I had considered a Graphlock gasket for a little bit, which requires less bolt stress, but Garlock said that this gasket would not be as leak tight as the BlueGard. My other concern is thermal expansion ... I have very long pipe runs (200-300 feet), and SS will grow and shrink, so for that reason I want very tight flanged joints. This is why I am steering away from red rubber. I am also not a huge fan of rubber gaskets since the installers usually keep tightening until they have metal to metal contact and the gasket has extruded. You can't torque the joint like with a BlueGard. Also, the red rubber will degrade over time.

Garlock didn't have any other recommendations for a compressed air system other than the Graphlock and BlueGard. The BlueGard seems to be the best for this application.

Thanks for your input.

 

[MJCronin]

Consider some of the new technology bolt coatings for this application.

I am a big fan of the XYLAN 1010/1014 series coatings over plain-old A193/A194 materials.

http://www.whitfordww.com/products-industrial.html

The manufacturer can give you details about marine environs.....but I have seen this coating system perform well on caustic soda service.

Some other systems mentioned in this article:

http://appliedbolting.com/pdf/coated_bolts_can_improve_constructability.pdf

let us know about your final decision....

Regards

-MJC