Dear KRISH, At first your soil chemistry, pH , corrosivity and Conductivity has to be obtained from Construction Records. Also a current assessment of the above parametrs are required by a qualified Civil Engineer. To mention a good and well applied IZS ( Inorganic Zinc Silicate) can withstand upto 390C dry heat but it is not well stable against acid and alkali. So you will be needing a suitable top coat. Epoxy Polysiloxane engineered product like PSX 738 is excellent for your case. But over and above better to do a CP impressed current instal. For additional protection if you find your backfill soil is having very high or very low Ph , you may treat or can use separate backfill soil. regards DM

Krish /MJC MJC is absolutely explicit and correct that at the project stage (design of piping system) compromises on quality and cost would reflect badly post operational service in 3-5 years time. Many a time, project contractors / major engineering consultants, give a design from compromise on quality and cheap cost considerations. In a blow down system (350 deg cent) design on net work under ground system should be carefully thought of. Clients or their project handling group, if ignorant, may not fully examine all future problems (likely to crop up in service) due to several limitations. Project cost and time of completion leads to such compromises for the project group to over look future corrosion problems. Replacing blow down system (to repeat the same mistake of below ground net work) but with improved protection coating or C.P may not be a total solution - from internal / external corrosion problems. Epoxy polysiloxane may need a curing at 200 deg cent (even for top coat) assuming that the siloxane variant - 90% volume content - is to stand temp close to 350-370 deg cent (which in your case is more than design temp of 350 deg cent). Siloxane Aluminium can stand upto 500 deg cent but with Zn silicate can stand 400 deg cent. Siloxane acrylic top coat can stand upto 550-600 deg cent but will be limited to 400 deg cent with Zinc Silicate primers. Even primary Zinc Slicate and top coat of epoxy poliysiloxane - assuming that these portection coating can stand a continuous blow down use of 350 deg cent in under-ground piping may not give a satisfactory service life after the next 3-5 years. Krish: I think you recognize this limitation of replacement now and plan for once in 3-5 years replacement / yet would still desire to use an underground waste blow down system (net working). Replacement planning and corrosion prevention with surface coating approaches may stand another 5 years. Trust this helps you C.V.Srinivasan Nishi Engineers Pvt Ltd India Aug 5, 2006 E-mail: nishi@vsnl.com >Krish, > >This sounds like one piping system that should not be >burried. > >Continuous blowdown systems are also subject to wastage from >the inside. Why subject the system to both internal and >external corrosion/erosion.....?? > >In my piping/plant design experience, you simply cannot >place any piping system underground without consequnces. >Manytimes it is cheaper and simpler for the installation >contractor to throw the system in the ground than it is to >design and install pipe racks, T-poles etc.....But, the >installation contractor does not have to operate the system. > >Rather than tyrying tosolve the external corrosion problem, >why not insulate and run the system above ground ?? > > >-MJC