Material in Sulfur environment

[octane]

At our site, major piping supplying hydrocarbons containing sulfur is of ASTM A106 Gr. B.
The service temperature is around 550 deg F with sulfur 0.07%.
Recently, for one of modification project in piping, we have contacted an engineering / construction contractor which suggested that the piping material must be ASTM A 335 Gr. P5 instead of the original carbon steel piping installed.

Your comments are required.

[ben]

I do not see any problem with A106 pipe in the mentioned service conditions.
It can survive this much temperature and sulfur concentration. What's the operational history? Any significant corrosion you may have noticed?
P5 although is a very useful among the low alloy steels in such service conditions up to 650 deg F but A106 should sustain up to 550 deg F.

[piiengineers]

With the low sulphur % ,A106 Gr.B can be used to up to 250-260 Deg.C.However,it depends on which service it is going to be used.If there is a possibility of sulphur concentration i.e column bottom then better to go for low alloy steel P5 piping since your operating temperature is in the border case.

regards,

[mechcolor]

There is no doubt in it that it's a border line case as I have seen people operating with carbon steel (killed with Si) like A 106 at temperatures up to 500 deg F and yet there are people who operate with same material at 550 deg F or something above it.
However, based on the sulfur concentration you may like to use the existing material based on the experience so far.
P5 obviously would be the most appropriate choice (technically) even up to 675 deg F.
Better seek the advise of your inspectors on this as what they have found so far in A106 piping.

[octane]

Thanks everybody for your replies.
The existing piping has completed almost 05 years of service and our inspection staff is satisfied as no metal loss due to corrosion has been noticed so far.
Should we go with A106 Gr. B for modification project?

[mechcolor]

As the inspection records are OK for the existing material throughout these 05 years you can take the decision of using the same material for modifications also.
If it was A53 piping instead of A106 then I would have said NO. Although both are carbon steel but A106 is killed with Si and can be marginally used in these service conditions.

[octane]

Thanks mechcolor for your advise.