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Ultrasonic Thickness Measurement Guide

dnv_logoThis guideline is prepared by Det Norske Veritas for ship owners, operators, yards and service suppliers approved for thickness measurements of ship's structure, in order to facilitate co-operation through a common understanding of the procedures for UTM ( ultrasonic thickness measurements) at Class Surveys. CAP is not covered by this guide.

Steel plates in the deck being replaced after UTM. Evenly corroded steel plates might look perfectly acceptable even at close-up distance. Thus, thickness measurements are an essential part of class surveys.

Terms and abbreviations

See also DNV Rules Pt.7 Ch.2 Sec.1 A100 for additional definitions.

Approval : Prog. No.402 "Approval of Firms Engaged in Ultrasonic Thickness Measurements of Ship's Structure". Set of requirements forming the basis for accepting a service supplier to do ultrasonic thickness measurements onboard steel ships for class. Included in Appendix B and C of this document.

Conditions : Conditions are issued to ship owners by class, in order to impose improvements, additional surveys orother actions to ensure compliance with rule requirements.

CA : A condition on behalf of a flag state that will be issued if the condition is related to statutory surveys where DNV has been authorised. ( Pt.1 Ch.1 Sec.3 B803 of the DNV Rules)

CAP : Condition Assessment Program. Voluntary hull condition survey, where a ship's hull, machinery or piping system is given one of the following ratings; 1 - Very good condition, 2 - Good condition, 3 -

Satisfactory condition or 4 - Poor condition ( below acceptable class standard ).

CAS : Condition Assessment Scheme. Increased survey/reporting scope, where the classification society will send a hull condition report to the flag state for their acceptance to let the ship continue trading. Applies to single skin tankers >15 years on their first intermediate or renewal survey after 5th. of April 2005.

Category I : Service suppliers approved to do thickness measurements for class onboard all DNV steel ships.

Category II : Service suppliers approved to do thickness measurements for DNV onboard fishing boats and non-ESP ships below 500 GT.

CC A : Condition of Class will be issued if a condition is related to requirements set by the rules. A CC is subject to specified rectification (e.g. repairs) or operation (e.g. survey) and shall be carried out within a given time limit, in order that the ship retain class. (Pt.1 Ch.1 Sec.3 B802 of the DNV Rules).

C.N.72.1 : Classification Notes No.72.1 "Allowable Thickness Diminution for Hull Structure"

ESP : Enhanced Survey Program. Requirements for planning, execution and reporting for hull surveys of oil/chemical tankers, obo and bulk carriers.

Excessive : corrosion An extent of corrosion that exceeds the allowable limit, so that steel must be replaced. Ref. Fig.2.1.

Extensive : corrosion An extent of corrosion consisting of hard and/or loose scale, including pitting, over 70% or more of the area under consideration, accompanied by evidence of thickness diminution.


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