A564 17-PH vs 316SS

[Ken_438]

Hi guys,

I am working on a technical evaluation for some valves. The Client valve datasheet specifies the stem material as 316 SS. However, the bidder is providing A564 17-4PH in lieu of this material.

Is this an acceptable alternative?

Valve service: process hydrocarbon (non-sour)
ASME CL 600
Design temp -29 to 200 C.

Thanks in advance for the feedback.

 

[EdStainless]

There are a lot of valve stems made from various PH stainless grades.
In general you need material that has been aged at a higher temp (at least 1025F, 1100F is better).
While this reduces the strength it improves toughness and reduces the sensitivity to SCC and hydrogen cracking.
Ask what the aging temperature is.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[racookpe1978]

Thank you for including valve temperature, service class and fluid, and pressure. The courtesy is appreciated.

 

[cap1a79]

The use of S17400(17-4 PH) has lower SSC & SCC resistance than SS 316 generally.
If the field is sour at the upstream that NACE MR 0175 is applied, it has very limited acceptance of environmental limit to use 17-4PH. (Refer to A.27 & A28 of NACE MR 0175).




Lee SiHyoung,
WorleyParsons Oman Engineering,

 

[EdStainless]

cap, in my experience high strength as-cold-drawn 316 and 17-4PH aged at 1100F or 1150F have no difference in CSCC resistance.
In fact I have seen them both fail by hydrogen embrittlement also. The 316 forms so much martensite when cold worked that it changes a lot.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[cap1a79]

Hi, Ed
Thanks for sharing your experience. I would understand the case that there is no difference is based on specfic testing condition. If you can, I would appreciate if you share the deformation rate, hardness of SS & testing environment(ex., ppm of chloride, H2S). Also, if it is published in official site, please let me know the title so that I would utilize it...

However, referring to some of other references (ex., NACE 08099, NACE MR 0175 environment limit), it is very hard to accept the application of S17400 instead of SS 316, generally. If there is an experiment supporting that S17400 can be used on behalf of SS 316, it should be the one that corresponds to or is harsher than the process conditions intended to use. To do so, detailed comparison of the process conditions and the experimental environment is necessary.

In this time, I would take a slightly difference approach.

1) Is it stem material which is non-pressure containing?(Stem belongs to valve trim and the valve trim is non-pressure containing)
If yes, there would be little issue of SSC & SCC for 17-4 PH. SSC & SCC do not occur under compressive force.

2) Is the connected pipe CS? If yes, 17-4 PH would be suitable. (17-4 PHSS has less corrosion rate than CS generally.)

3) I would assume that there is no chloride & oxygen is controlled for process hydrocarbon.





Lee SiHyoung,
WorleyParsons Oman Engineering,

 

[EdStainless]

I can't share test data because it belongs to a customer of ours.
By the time you cold draw 316 to reasonable strength (110ksi min yield, 150ksi min UTS) in order to get properties similar to 17-4PH H1150 you have very low ductility (<8%).
This requires cold draw of >40% reduction.
If you did this with an austenitic stainless that does not form martensite on deformation (such as 21-6-9, Nitronic 40), the resulting material is tougher and still has resistance to HE.
However both will easily CSCC.

There is no way that you could use annealed 316 in a valve stem, not with such a low yield strength.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[cap1a79]

One more thing I would share is that if pitting is considered, definitely 17-4 PH does not have same resistance as ss316's.

Pitting index
PREN for 17-4 PH --> above 16
PREN for SS316 --> above 23.1

Lee SiHyoung,
WorleyParsons Oman Engineering,