Heat Tracing Sulfuric Acid Pipe

[btg]

I've got to run approximately 400' of above ground pipe from a 98% sulfuric acid tank to our acid header. I live in South Louisiana and our lowest monthly average temp is between 40-45 degrees F. The minimum flowrate of acid would be 1 gpm. I'm wondering the need to heat trace the piping. Is there any way I can get away with just insulating the pipe? The piping from the header is all traced. This piping is new piping and obviously costs would be much less without tracing. Thanks.

 

[TD2K]

I don't know what the freeze temperature is of the acid versus the ambient temperatures you list (if that is your concern).

Insulation will slow down how long it takes the contents to reach ambient temperature but it doesn't stop the loss of heat. You need to look at how you are going to operate this line and then make the decision if you need to heat trace or if insulation is suffient.

 

[unclesyd]

We operate a much longer 98% H2SO4 line at the same latitude as you are. There is no insulation on the line, it is only painted. The flow is intermittent, though daily. Being uninsulated facilitates the periodic inspection and repair of the line. The line is 2" Sch 160. The line is installed to be self draining or can be maintained full. Both end are N2 blanketed by means of conservation vents.

There are a lot of other considerations in the design of a concentrated sulfuric line and the transfer of the acid. There are several pamphlets out on the design and maintenance of said line. I know Monsanto Enviro-Chem had one along with some others. I think NACE has something out.
If not installed and maintained a conc. H2SO4 can be a headache, 1st Class.

 

[MJCronin]

btg,

I have specified carbon steel tanks holding 98% H2SO4.

Usually, the problem with this concentrated acid is corrosion due to dillution (a corroded band appears on the inside of the tank where dilluted acid forms) or corrosion due to acid velocity within a tank of piping system (a good rule of thumb is to keep the velocity very low... 2-4 feet/second)

Corrosion of carbon steel accelerates when this acid is stored above 125F....Lower temperatures are better

I agree with "unclesyd"........I do not understand why you would want to insulate or heat trace this piping. Heavy walled ( Sch 160 ?) carbon steel piping is best

There is some good H2SO4 information on the internet, available from the acid vendors....

The NACE standard mentioned above applies to tanks built since 1994.

These tanks often incorporate some or all of the recommendations listed in NACE International, Recommended Practice RP3294-94 (Design, Fabrication, and Inspection of Tanks for the Storage of Concentrated Sulfuric Acid and Oleum at Ambient Temperatures).

Perhaps, you are thinking of heat tracing to increase the flow rate ? Is the acid pumped or somehow gravity fed ?

My thoughts only

MJC


"There comes a time in the affairs of man when he must take the bull by the tail and face the situation." W.C. Fields

 

[unclesyd]

A common problem in concentrated sulphuric acid piping that is usually overlooked is the O2 corrosion in the vapor area in the piping. This corrosion manifest itself as a grove in the piping at 0̊. This is easily found by periodic RT and/or UT. We handled it by rotating the pipe when the grove depth approached the retiring limit. We used 0.125" wall as the very minimum on H2SO4 lines
As I mentioned before it is best to keep your system blanketed by dry N2.

 

[mariodupuis]

BTG,

The freezing point of 98% sulfuric acid is 30F. At 99% sulfuric acid the freezing point is 40F and at 100%, the freezing point is 50.7F. So, depending of the concentration varation on your sulfuric acid, you can have some problems is your pipe are not kept over this temperature.

 

[btg]

Thanks for your responses. I've been told that 98% sulfuric will start becoming sludge-like at around 50 degrees which could create pumping issues. Our policy is to insulate and heat trace all sulfuric lines but I was trying to find out if it's really necessary since the flow is not intermittent and the tank would create a heat sink that would keep the acid at fairly constant temp. year round. The line is a 3" Kynar coated carbon steel line.

 

[unclesyd]

We tried two different vendors of Kynar lined pipe for H2SO4
and neither was satisfactory.
If you are having good results with the Kynar lined pipe, if possible please post a supplier.
The line has been moved over a walkway and if there is a leak we have people problems.