Shaft Material Memo_111573684.pdf

UNITED STATES DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration Office of Marine and Aviation Operations

NOAA Ship Ferdinand R. Hassler (S-250)

UNH

Judd Gregg Marine Research Complex

Wentworth Rd, New Castle, NH 03854

05 MAR 2019

MEMORANDUM

FROM: Sandra J. Wyman, PE

Port Engineer, NOAA Ship FERDINAND R. HASSLER (S-250)

SUBJ: Shaft Material Deviation

REF: ABS Class Additional Requirements 208 and 209

ENC: 1. Drawing M286-243-FM01-04

2. Shaft Diameter Calculations

3. Aquamet Material Data Sheet

This memo formally requests technical review to substitute Aquamet 22 H.S., (UNS S20910) for

Aquamet 17 (UNS 17400) as the tail shaft material for NOAA Ship FERDINAND R. HASSLER

(S-250). The proposed material is sold under multiple trade names including but not limited to

Aqualloy 22 HS, XM-19 HS, and Nitronic 50 HS, all meeting the requirements of UNS S20910.

Enclosure 1 is the current as built shaft arrangements drawing. Enclosure 2 is a set of shaft diameter calculations performed in accordance with ABS Steel Vessel Rules Under 90m in

Length 2018, Part 4 Ch 3 Section 1-7. Enclosure 3 is a material properties data sheet containing information on both the original shaft material, Aquamet 17 and the proposed replacement material Aquamet 22 H.S.

The vessel currently has additional class requirements to remove and inspect the tail shafts at every dry docking. The original tail shafts were found to be severely pitted after 5 years of service and were replaced in June 2016. The replacement shafts were removed on 25 February

2019 and were also found to be heavily pitted. The root cause for the high level of corrosion appears to be the use of a stainless steel with mediocre pitting corrosion resistance in a stern tube without a stern tube flushing system that runs independently of the main engine.

In stainless steel alloys the proportion of chromium, molybdenum, and nitrogen have been shown to have a significant effect of susceptibility to pitting and crevice corrosion. The Pitting

Resistance Equivalent Number (PRE) is used a means of comparing similar alloys.

PRE = % Cr + 3.3 x %Mo + 16 x %N

Aquamet 17 is a high strength stainless steel allow with known pitting issues when exposed to stagnant sea water. It has PRE of 14.5-16.5. Aquamet 22 HS has a PRE of 24.3-38.9. For reference 316 stainless steel has a PRE of 22-28.

S e e A

B S H o u s to n L e tt e r R e f T D a te d

-M

A R

-2

The proposed material substitution meets the strength requirements (125 ksi UTS) to outfit the ship with a 6.5” dia shaft (as designed) and provides a significant improvement in corrosion resistance.

S. J. WYMAN

S e e A

B S H o u s to n L e tt e r R e f T D a te d

-M

A R

-2