How severe is the caustic?  In general Ni alloys don't like high pH, especially if the conditions are reducing.
I will try to find you some corrosion data for "C" type alloys in in caustic.

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Corrosion never sleeps, but it can be managed.
http://www.trenttube.com/Trent/tech_form.htm

EdStainless,

Thanks for your quick repley. The conditions are as follows:
HCl 30% 5 barg @ 60 deg C / NaOH 22% 5 barg @ 60 deg C.

I would probably go for a PFA/PTFE lined sample valve.  We use a lot Manufacturers whe have used CRP-Flexrite, Technova, Halwachs.  Can get a bit pricy but do the job.  They have some good safety features most of them will design around a standard valve for unusual duties.

Good luck.

Biggy

According to Philip A Schweitzer the following Hastelloy grades are resistant to both sodium hydroxide as well as hydrochloric acid: (Temperature degree Fahrenheit). The tabled value indicates the resistance is "good".
"Good" is defined as <20 mils/year.

HCl                Dilute 20%   35%   38%   50%
Hastelloy B/B-2    180    220   200   140   80
Hastelloy C/C-276  160    150   140   140   80

NaOH               10%    15%   30%   50%   70%  Conc
Hastelloy B/B-2    230   210   250   250   220   200
Hastelloy C/C-276  230   210   210   210   220   120