Maintenance And Inspection; Frequently Asked Questions (Faq) - HOLLAND MARINE PARTS Jet Thruster JT-30 Installation Manual & Users Manual

Marine
Holland
Inspection
Parts
Materials
Heijningen

Maintenance and Inspection

All parts have been made of corrosion resistant materials. However under extreme conditions
corrosion is possible. For that reason we advice an inspection interval of 6 month.
1.5 Nozzles
Inspect the nozzles once every six month on corrosion and fouling from the outside of the
vessel. If corrosion or fouling can be seen, remove it with a brush and inspect the surface (and
welds if applicable) again on pitting corrosion.
1.6 Valves/Nozzles Threading
Inspect once every six month the threading of the couplings on leakages. If leakages are found,
possibly crevice corrosion of the threading occurs. Loose the coupling and inspect it on
corrosion of the threading's internal and external.
1.7 Pump
During longer stand still periods it is recommended to store the pump internals in air, or in fresh
water. If seawater or brackish water is in the pump for a longer time (month), we recommend to
inspect the impeller on corrosion problems.

Frequently Asked Questions (faq)

Q: For the nozzles: Can a coating help to avoid corrosion?
A: Yes, a coating can help on the external part. Internally the nozzles cannot be coated as the
water flow is too high. A coating will loosen from the stainless steel surface.
Q: How should stainless steel be coated?
A: Stainless steel can be coated, but the adhesion of the coating always will be less good
compared to carbon steel. The coating procedure is similar to carbon steel:
1. Proper surface preparation by grid blasting. High roughness is of great importance.
2. The surface must be completely clean, particularly free of chlorides (salt).
3. Use several layers of (primer) epoxy, according to marine coating specs.
Q: What protection will polishing the stainless steel surface guarantee?
A: Polishing always is good for two reasons:
1. Corrosion resistance will improve.
2. Biofouling and MIC will be reduced.
Q: Can biofouling promote corrosion, such as crevice corrosion or MIC?
A: Yes, biofouling preferably must be removed.
Q: How can pitting corrosion be repaired?
A: If the pits are not deep, the can be grinded out smoothly succeeded by polishing the surface.
If the pits are deep, the need to be welded and the surface must be grinded again.
Doc. No. 214065
D-010-04
D-010-06
and Maintenance Jet Thrusters
Selection and Corrosion
Rev. No. 00 Rev. Date 17 juli 2014 6
Page 3 of
95
Holland Marine Parts