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Oil, Gas, Petrochemical Industry News
News Release from: Tube Tech International | Subject: WHRU cleaning
Edited by the Processingtalk Editorial
Team on 04 October 2007
Tube Tech cures for fouled plant can
save money!
Before attacking a blocked WHRU offshore, and undertaking costly removal, operators are learning that specialist cleaning contractor Tube Tech international should be called in first!
Cleaning a blocked WHRU conventionally involves costly cutting off of the serpentine bends and re-welding after cleaning; this is no longer necessary When any heavy plant item on an offshore platform fails, it means highly involved and often hazardous operations to disconnect it, move it off line, and then transfer it to a supply ship to be taken ashore for repair
This article was originally published on Processingtalk on 19 Oct 2007 at 8.00am (UK)
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Plant-like Waste Heat Recovery Units (WHRUs) and shell-and-tube heat exchangers are comprised of coiled tubes that can become restricted or blocked with carbon deposits.
Standard industry approaches to solving the blockage problem are:.
* Bypass the fouled unit.
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* Cut off the U-bends, clean the straight tubes and then weld the U-bends back in place.
* Replace the complete unit.
None of these options are completely satisfactory.
Bypassing the unit causes inefficient burning of fuel and higher platform operating costs.
Cutting the U-bends is time-consuming, with no guarantee there will be access to reattach the bends.
When the exchanger is returned to duty, it under-performs because deposits remain in the U- bends, so the exchanger shortly has to be cleaned again.
Replacing the complete unit is the most expensive option due to the cost of the replacement unit and platform production loss from lengthy downtime.
This recently happened, and provides an interesting example, proving the problems and options available.
A WHRU on a North Sea platform became restricted and had to be shutdown.
The unit already had been disconnected and transported ashore, when the operator decided to have Tube Tech inspect the unit with a view to 'trying to clean it' before ordering a USD500,000 replacement.
It can take up to a year for a new replacement unit to be installed because of the six-month manufacturing lead-time, plus WHRUs can only be taken off line once a year when the platform gas turbines are down for maintenance.
Tube Tech established a three-stage plan.
Phase one was locating the position and length of blockages within the unit; phase two was a systematic unblocking; and then phase three was a thorough cleaning.
This did not involve removing any U-bends.
Because of the size of the WHRU, two 14.5-metric ton (14.9-ton) cranes were used to change the position of the unit during cleaning.
The WHRU was de-scaled, unblocked in two weeks, and restored to peak efficiency.
The operator saved GBP150,000 (USD297,350) in possible manufacturing costs and subsequent rig production losses through on-site cleaning.
Obviously calling in Tube Tech for advice will be the first item on their list when future similar WHRU problems develop, before shipping the unit ashore.
After considering the further cost implications of a failure in one of two other WHRUs they owned, the operator contracted Tech Tube to clean both units on-site as a precaution.
A serpentine shell-and-tube exchanger on a Persian Gulf platform developed a similar fouling problem.
Tube Tech decided to use a seawater-fed jetting system they had developed, that appeared to have potential for this form of cleaning.
The jetting system features low-flow, high-pressure water delivered through unblocking and de-scaling nozzles, supplemented with a specially-developed U-bend nozzle which can negotiate close-radius bends.
Even in the limited confines of the platform, a comprehensive on-site clean was completed on time and on-budget.
The Author of this report, Mike Watson, is the founder and Managing Director of Tube Tech International, the specialist tube and pipeline cleaning company.
For further information please visit the website.
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