class PK
{
    decimal? Value ;
}

void SetNewPKs
{
    (Tag as List<Blank>).ForEach(x => SetNewPK(x)); // на выходе все  b.PK.Value одинаковы :(        
}
void SetNewPK(Blank b)
{
    // манипуляции с b.PK.Value  - значения получаю самые разные
     return;            
}

 /// <summary>
    /// Заготовка
    /// </summary>
    public class Blank : EntityBase
    {
        #region Fields and Proporties

        public int IdRecord { get; set; }
        /// <summary>
        /// Размер сечения
        /// </summary>
        public string SizeSection { get; set; }
        /// <summary>
        /// Масса слитка
        /// </summary>
        public decimal Mass { get; set; }
        /// <summary>
        /// Получено
        /// </summary>
        public int? InputPieces { get; set; }
        /// <summary>
        /// Примечание
        /// </summary>
        public string Note { get; set; }
        /// <summary>
        /// Дата создания
        /// </summary>
        public DateTime Date { get; set; }
        /// <summary>
        /// Номер смены
        /// </summary>
        public Nullable<int> ShiftNumber { get; set; }
        /// <summary>
        /// Длинна
        /// </summary>
        public string Length { get; set; }
        /// <summary>
        /// Расходный коэф.
        /// </summary>
        public TypeРК TypeРК { get; set; }
        /// <summary>
        /// Карта плавки
        /// </summary>
        public CardMelting CardMelting { get; set; }
        /// <summary>   
        /// Направление
        /// </summary>
        public BlankType BlankType { get; set; }
        /// <summary>   
        /// Утверждено
        /// </summary>
        public Approve Approve { get; set; }
        /// <summary>
        /// Собственность
        /// </summary>
        public Ownership Ownership { get; set; }
        /// <summary>
        /// Родительская таблица
        /// </summary>
        public string ParentTable { get; set; }
        /// <summary>
        /// Номер
        /// </summary>
        public int? Number { get; set; }

        /// <summary>
        /// Профиль
        /// </summary>
        public Profile Profile { get; set; }

        #endregion

        #region Methods

        public void ReplaceMe(Blank from)
        {
            this.Approve = from.Approve;
            this.BlankType = from.BlankType;
            this.CardMelting = from.CardMelting;
            this.Date = from.Date;
            this.Id = from.Id;
            this.Length = from.Length;
            this.Mass = from.Mass;
            this.Note = from.Note;
            this.Ownership = from.Ownership;
            this.ShiftNumber = from.ShiftNumber;
            this.SizeSection = from.SizeSection;
            this.TypeРК = from.TypeРК;
            this.InputPieces = from.InputPieces;
            this.Number = from.Number;
            this.IdRecord = from.IdRecord;
            this.ParentTable = from.ParentTable;
            this.Profile = from.Profile;
        }
        #endregion
    }


void SetNewPK(Blank b)
        {
               b.TypeРК = _allTypesРК.Find(x => x.Id == 8); // проставим тип
                
                switch (b.BlankType.Id)
                { 
                    case 1 :
                        if (b.CardMelting != null && b.Profile != null)
                            b.TypeРК.Value = new SqlDataAdapterTypesPK(Global.GlobalSettings.Connection).GetDefaultPKValue(null, null, b.Profile.Id, b.Date, b.CardMelting.Steel.Id);
                        else
                            b.TypeРК.Value = null;
                        break;
                    
                    case 2 :
                    case 3 :
                        b.TypeРК.Value = new SqlDataAdapterTypesPK(Global.GlobalSettings.Connection).GetDefaultPKValue(null, null, null, b.Date, b.CardMelting.Steel.Id);
                        break;

                    case 4 :
                        b.TypeРК.Value = new SqlDataAdapterTypesPK(Global.GlobalSettings.Connection).GetDefaultPKValue(52, 15, null, b.Date, b.CardMelting.Steel.Id);
                        break;
                }
                
                // Проставить подгруженное PK по-умолчанию в текстбокс
                if (_editFormat == EditFormats.One)
                    txtTypePKValue.Text = (b.TypeРК.Value.HasValue) ? b.TypeРК.Value.ToString() : "";
            }
            return;   
        }

b.TypeРК.Value = new SqlDataAdapterTypesPK(Global.GlobalSettings.Connection).GetDefaultPKValue(null, null, null, b.Date, b.CardMelting.Steel.Id);
                        break;

  public decimal? GetDefaultPKValue(int? OID_SubWorkCenter, int? OID_SubOperation, int? idProfile, DateTime dateBegin, int idSteel)
        {
            decimal? result = null;

            SqlCommand cmd = CreateCommand(StProcs.GetDefaultPK);

            cmd.Parameters.Add(Parametrs.dateBegin).Value = dateBegin;
            cmd.Parameters.Add(Parametrs.idSteel).Value = idSteel;

            if (idProfile.HasValue)
                cmd.Parameters.Add(Parametrs.idProfile).Value = idProfile;

            if (OID_SubWorkCenter.HasValue)
                cmd.Parameters.Add(Parametrs.OID_SubWorkCenter).Value = OID_SubWorkCenter;

            if (OID_SubOperation.HasValue)
                cmd.Parameters.Add(Parametrs.OID_SubOperation).Value = OID_SubOperation;
            
            OpenConnection();
            SqlDataReader reader = cmd.ExecuteReader();
            reader.Read();
            if (!reader.IsDBNull(reader.GetOrdinal("Value"))) 
                result = reader.GetDecimal(0);
            CloseConnection();
            return result;
        }